Proceedings Volume 7382

International Symposium on Photoelectronic Detection and Imaging 2009: Laser Sensing and Imaging

Farzin Amzajerdian, Chun-qing Gao, Tian-yu Xie
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Proceedings Volume 7382

International Symposium on Photoelectronic Detection and Imaging 2009: Laser Sensing and Imaging

Farzin Amzajerdian, Chun-qing Gao, Tian-yu Xie
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 24 August 2009
Contents: 2 Sessions, 195 Papers, 0 Presentations
Conference: International Symposium on Photoelectronic Detection and Imaging 2009 2009
Volume Number: 7382

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7382
  • Laser Sensing and Imaging
Front Matter: Volume 7382
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Front Matter: Volume 7382
This PDF file contains the front matter associated with SPIE Proceedings Volume 7382, including the Title Page, Copyright information, Table of Contents, the Conference Committee listing and the Introduction.
Laser Sensing and Imaging
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Laser radar work at FOI
This paper will give an overview on some recent laser radar work at the Swedish Defence Research Agency (FOI). The activities include range gated imaging, scanning and 3 D ladars and flash imaging 3 D ladars. Example of data from different campaigns will be presented together with examples of modelling efforts. Example of potential applications will be discussed.
Exploiting range imagery: techniques and applications
Practically no applications exist for which automatic processing of 2D intensity imagery can equal human visual perception. This is not the case for range imagery. The paper gives examples of 3D laser radar applications, for which automatic data processing can exceed human visual cognition capabilities and describes basic processing techniques for attaining these results. The examples are drawn from the fields of helicopter obstacle avoidance, object detection in surveillance applications, object recognition at high range, multi-object-tracking, and object re-identification in range image sequences. Processing times and recognition performances are summarized. The techniques used exploit the bijective continuity of the imaging process as well as its independence of object reflectivity, emissivity and illumination. This allows precise formulations of the probability distributions involved in figure-ground segmentation, feature-based object classification and model based object recognition. The probabilistic approach guarantees optimal solutions for single images and enables Bayesian learning in range image sequences. Finally, due to recent results in 3D-surface completion, no prior model libraries are required for recognizing and re-identifying objects of quite general object categories, opening the way to unsupervised learning and fully autonomous cognitive systems.
Detection of organized airflow in the atmospheric boundary layer and the free atmosphere using a 3D-scanning coherent Doppler lidar
Y. Fujiyoshi, K. Yamashita, C. Fujiwara
We will overview organized airflows, turbulent and laminar structures in the atmospheric boundary layer and the free atmosphere newly detected by a 3D-scanning coherent Doppler lidar system (3D-CDL). Study of clouds becomes important especially in recent years, since they play an essential role in global climate systems and the earth environment. The aerosol-cloud interaction is not enough to evaluate aerosol indirect effect. Air-motion is the key factor that connects aerosols and clouds especially in the atmospheric boundary layer. Using the 3D-CDL, we detected such various kinds of atmospheric phenomena as plume, streaks, invisible dust-devils, fog, fire-work, local front, downburst, wake of buildings, gravity waves, Kelvin-Helmholtz instability waves, sea-breeze fronts, fine-weather cumulus, low-level stratus, mid-level clouds, mammatus clouds and cirrus clouds etc. Some of these phenomena are firstly observed by the 3D-CDL. We simulated some phenomena by using a Large Eddy Simulation (LES) model and compared the simulated structures with those observed by the 3D-CDL.
Development of an airborne wind measurement system
Hamaki Inokuchi, Eiichi Endo, Toshiyuki Ando, et al.
Accidents to airliners caused by air turbulence have been increasing in recent years. At present there is no sure way of avoiding encounters with clear air turbulence (CAT) because conventional airborne weather radars cannot detect turbulence in clear conditions. The Japan Aerospace Exploration Agency (JAXA) is therefore developing a Doppler LIDAR (Light Detection and Ranging) which can measure wind speeds ahead of an aircraft even in clear air. Turbulence prediction in flight has already been demonstrated using experimental Doppler LIDARs, and the latest prototype aims at turbulence detection up to 5 nautical miles (9 km) ahead at jet airliner cruising altitudes. Wind velocity measurement by LIDAR is difficult at high altitude because of low aerosol particle density. Regular atmospheric observation flights are therefore being made to establish the basic specifications of a practical device. Furthermore, since air turbulence information should be displayed on the flight deck, a graphical turbulence display is also being studied. This paper describes the development of the airborne wind measurement system and presents examples of flight experiment results.
Diode pumped monolithic single frequency solid state lasers for coherent detection applications
Chunqing Gao, Mingwei Gao, Zhifeng Lin, et al.
Laser diode pumped single frequency, narrow-linewidth solid state lasers have important applications in coherent detection systems. This paper reports two kinds of diode pumped single frequency solid state lasers with wavelengths of 1319nm and 2μm, respectively. The LD pumped monolithic non-planar ring resonators (NPRO) are designed to generate the single frequency operation. High efficiency single frequency lasers were obtained in the 1319nm NPRO Nd:YAG laser and the 2μm NPRO Tm:YAG laser.
Study on high power semiconductor laser arrays and output beam shaping
Guojun Liu, Baoxue Bo, Xiaohui Ma, et al.
Semiconductor Lasers (also known as Laser Diodes, LDs), have many unique properties and advantages and found wide applications in variouse fields. The super high conversion efficiency of high power single emitter semiconductor lasers and their arrays, commonly achievable values of them being in the range of 50%-80%, makes them particularly suitable for applications as the ideal pumping source for solid state lasers and also as widely used in material processing and medicine. Yet semiconductor lasers also have shortcomings, the poor beam quality of multi-mode semiconductor lasers and laser arrays usually severely restricted their applications. The present paper mainly addresses the semiconductor laser arrays design and fabrication technologies, with particular emphasis placed on the beam shaping principles and methods. The high power semiconductor lasers in the wavelength range between 800nm and 1100nm have been reviewed and analyzed. The topic of the electrical-to-optical conversion efficiency enhancement has been addressed in some detail. The high power single emitter lasers and LD bars have been fabricated and their performance characterized. The beam divergences of LDs in the vertical and parallel directions have been addressed and analyzed. The beam collimation has been analyzed and experimentally performed for the single emitter and LD bars. Beam combining methods and fiber coupling have been summarized and experimentally verified, with specific efficiency data for beam combining and fiber coupling being presented and analyzed.
Investigation of ultrashort pulse laser propulsion using time-resolved shadowgraphy and torsion pendulum
Xiao-nong Zhu, Nan Zhang
Laser pulses with different pulse durations between 50 fs and 12 ps are used to ablate different types of solid targets. With the help of time-resolved shadowgraphy, the ultrafast dynamics associated with femtosecond laser ablation of solid materials is experimentally investigated based on the commonly used pump-probe technique. It is revealed that both photothermal and photomechanical mechanisms exist in the ablation processes for laser fluence far above the target ablation threshold. From the recorded shadowgraphs, it is revealed that the material ejection due to femtosecond laser ablation of solid materials has a typical velocity of 105 - 104 m/s. Such high jet velocities can lead to specific impulse of 104 - 103 s, which is much higher than the upper limit of the specific impulse of chemical propulsion (500 s). The so-called ablative laser propulsion with high specific impulse can be thus realized. Momentum coupling coefficient is determined through using a homemade torsion pendulum with a minimum measurable momentum of ~2x10-9 N·s. The dependence of the ultrashort laser ablation generated momentum is investigated on laser energy fluence and pulse width. The main findings include: 1) As the pulse width increases, the laser generated momentum first increases rapidly and then remains almost constant; 2) For 50 fs pulses, optimal laser fluence exists that leads to the maximum momentum for aluminum and copper targets. At the optimal laser fluence, it is mostly the photomechanical mechanism that is responsible for material removal, and in this case the ablated material also has relatively lower jet velocity.
3D imaging LADAR with linear array devices: laser, detector and ROIC
Shumpei Kameyama, Masaharu Imaki, Yasuhisa Tamagawa, et al.
This paper introduces the recent development of 3D imaging LADAR (LAser Detection And Ranging) in Mitsubishi Electric Corporation. The system consists of in-house-made key devices which are linear array: the laser, the detector and the ROIC (Read-Out Integrated Circuit). The laser transmitter is the high power and compact planar waveguide array laser at the wavelength of 1.5 micron. The detector array consists of the low excess noise Avalanche Photo Diode (APD) using the InAlAs multiplication layer. The analog ROIC array, which is fabricated in the SiGe- BiCMOS process, includes the Trans-Impedance Amplifiers (TIA), the peak intensity detectors, the Time-Of-Flight (TOF) detectors, and the multiplexers for read-out. This device has the feature in its detection ability for the small signal by optimizing the peak intensity detection circuit. By combining these devices with the one dimensional fast scanner, the real-time 3D range image can be obtained. After the explanations about the key devices, some 3D imaging results are demonstrated using the single element key devices. The imaging using the developed array devices is planned in the near future.
Airborne and spaceborne laser sounding technology and applications
Yihua Hu, Min He, Nanxiang Zhao
Airborne and spaceborne Laser sounding technology has been greatly improved, and they play important role in both science and economy. Basing on our study, airborne laser 3D imaging technology for earth observation, the data processing technology for laser sounding target, and laser altimeter for lunar sounding of China are discussed. Finally, the future development about space laser sounding is discussed.
Complex swept source optical coherence tomography with ultra-small fiber probe for biomedical imaging
We demonstrate a catheter-based complex swept-source optical coherence tomography (SS-OCT) system using a 3x3 Mach-Zehnder quadrature interferometer and an ultra-small optic probe. Design and fabrication of fiber lens for ultrasmall optic probes are presented first. We compare in detail measured performance with expected theoretical performance. Then, we present a 3x3 Mach-Zehnder quadrature interferometer to acquire a complex interferometric signal for SS-OCT. We introduce an unbalanced differential detection method to improve the overall utilization of optical power and provide simultaneous access to the complementary phase components of the complex interferometric signal. No calculations by trigonometric relationships are needed. We compare the performance for our setup to that of a similar interferometer with a commonly used balanced detection technique. We demonstrate complex conjugate artifact suppression of 27 dB obtained in our swept-source optical coherence tomography using our unbalanced differential detection. OCT in vivo and ex vivo images shown in this presentation indicate that our catheter-based complex SS-OCT system is capable for imaging of biomedical tissues and inside organs for human and animals.
Simulated detection and inversion of multi-species in atmosphere with a supercontinuum LIDAR
Zhengyu Zhang, Shouhuan Zhou, C. Russell Philbrick
The large band-with of super continuum Laser permits long path examination of large continual spectral regions to measure multi-species present simultaneously along the path. Herein statistical calculation and inversion with MLE on base of multivariate normal distribution model given focus on testing engineering capability of simultaneous multi-species detection with MODTRAN4 return under different cases of widely varied noise and atmospheric aerosol extinction. Simulation on available waveband of commercial super continuum Laser produce perfect results that agree with true concentration of multi-species and show complete approach advantages of abundant wavelength lines selected with a super continuum LIDAR: high accuracy, low FAR and robust result.
High-power Nd:YAP blue laser by intracavity summing frequency
Yong-ji Yu, Guang-yong Jin, Chao Wang, et al.
Recently, continue-wave blue laser generated by frequency doubling of the diode-end pumped neodymium doped lasers operating at the 4F3/24I9/2 transition have been extensively explored. But this way is limited by the considerable re-absorption loss caused by thermal population of the lower laser level for the oscillation of quasi-three-level laser. Another efficient way to obtain blue laser is based on summing frequency of the neodymium doped laser operating at the 4F3/24I13/2 transition. Unlike the three-level system of the 4F3/24I9/2 transition, stimulated emission at the 4F3/24I13/2 transition is a four-level system that can provide a low-threshold and stable laser output due to the lack of sensitive temperature dependence of the transition rate. High power blue laser has been achieved in this way. In this paper, we report a high power blue laser output is obtained by intracavity sum-frequency-mixing of a diode-side-pumped Q-switched Nd:YAP laser operating at 1.3μm with two LBO crystals. An LBO crystal with type-I critical phase matching and the other crystal with type-II critical phase matching were used for the second harmonic generation and the third harmonic generation, respectively. In view of the analysis of the cavity stability, a four-mirror folded cavity was designed and the output characteristics were theoretically analyzed. Experimental characteristics obtained were shown to be in agreement with the theoretical analysis. 3.2W average power at 447nm and 1.3W average power at 446nm blue laser outputs were achieved at 1kHz with pulse width of 10ns from the 1341.4nm laser beam polarized along the c crystalline axis and the 1339.2nm laser beam polarized along the a crystalline axis, respectively. The 447nm blue laser corresponds to a red-to-blue conversion efficiency of 30%.
Q-switched Nd:YAG laser alternate symmetric side pumped by diode arrays
Xin-yu Chen, Guang-yong Jin, Chao Wang, et al.
The laser diode side-pumped electro-optical Q-switced Nd:YAG laser of high single pulse output energy were studied. Two alternated semicircular LDA module was used to directly side pump the Nd:YAG crystal of a series of two-rod. Each module consists of 30 laser diode which peak power is 100W. KD*P crystals is used as the electro-optic Q switch. And the ABCD law of the Gaussian beam propagation is applied to calculate the area of the stability of the resonator cavity, and a more reasonable parameters of the resonant cavity is given. A 1064nm dynamics laser that maximum output energy of 140mJ and pulse width of 10ns is obtained at a repetition rate of 20Hz when the pump energy is 1200mJ.The optical-optical conversion efficiency is 11.7%.
Super-resolution in focusing system by three-zone pure phase plate
Xiumin Gao, Qiufang Zhan, Jinsong Li, et al.
Superresolution is very important in imaging and optical storage systems, and has attracted much attention. In this article, concentric three-zone phase plate with 0, pi, 0 phase variation has been investigated numerically to show that this kind of phase plate can be used to obtain three dimensional superresolution. Focal depth, focal shift, full width half maximum, superresolution effect are listed for different radii of the phase zones, which paves the way for design of the phase plate, such as for purpose of radial superresolution with high focal depth in optical storage.
Investigation of balanced detection and receiver for coherent lidar
Chunhui Wang, Long Gao
Signal detection plays a very important part in information times, which includes optical signal detection and electronic signal detection. Without question, 21 century is an optical times, so the importance of the optical signal detection becomes obvious. Optical detection includes direct detection and indirect detection (coherent detection). Direct detection is a method which only measures the amplitude of the signal and also be used in the measurement for strong signal. In contrast in indirect detection other parameters of the received electrical field can be modulated, such as its amplitude, frequency or phase. Coherent detection can be performed using two different techniques: heterodyne detection and homodyne detection. The coherent detection has much more sensitivity improvement over direct detection. However, some errors arise because of the two unstable signals, i.e., local beam and signal beam. Therefore, balanced detection technique can solve the question. In this paper, balanced detection technique was analyzed, which also was applied in signal measurement for lidar. Firstly, Mathematical modeling of the balanced detection process is deduced. Secondly, a numerical simulated system is established with software LABVIEW. Signal-to-noise ratio of the balanced detection is much two times than that of normal coherent detection technique. Furthermore, this balanced detection technique, which also be used in measurement for wind, not only Doppler shift can be obtained, but whether the Doppler shift is positive or negative can be distinguished, in other words, can know the direction of wind. Last but not least, the experiment results is well consisted with the simulated results, which shows that signal-to-noise ratio has been improved obviously.
A high-speed acquisition and processing system of the laser speckle signal on the magnetic fluid
Qiu-hua Wan, Yong Jiang, Shao-chang Su, et al.
In order to achieve the dynamical detection and real-time analysis of the movement status of the magnetic fluid, according to the difficulties of the detection of the magnetic fluid, established a high-speed acquisition and processing system of laser speckle signal on the magnetic fluid. First of all, the FPGA (EP2C8T144C8N) drived the linear array CCD(TCD1501D) to scan in the corresponding time sequence given by the computer, collected the laser speckle interferometric image in rapid change on the surface of the magnetic fluid, which followed the movement of the magnetic fluid, and the signal collected by CCD was converted into the digital data through the high-speed A/D convertor and stored into the internal buffer FIFO of the FPGA, whose width and depth were designed by the user as required. Then, the FPGA sent the digital signal of the laser speckle interferometric images into the computer through the USB2.0 highspeed differential bus, whose transmission rate can reach 480Mb/s in theory. Finally, the distribution of the laser speckle on the magnetic fluid was messy and random, which carried certain information about the surface of the magnetic fluid, based on the theories of the statistic correlation and the subdivision of images, analysing and processing the laser speckle interferometric images, indirectly got the movement status of the magnetic fluid under the electromagnetic field. The experimental results show that: the High Speed Acquisition and Processing System has the advantage of full-court, non-contact, non-invasive, high-precision and high reliability and so on. The detection resolution of high speed acquisition and processing system is superior to 1m and the sample rate is 3Msps, which basically meets the requirements of the magnetic fluid movement state detection.
Survey of automatic target recognition technology for LADAR
Xiao-qing Chen, Jun-guo Ma, Hong-zhong Zhao, et al.
With the development of laser technology, Three-Dimensional (3D) imaging sensors based on Laser Radar (LADAR) gradually possess vast application in complicated battlefield of modern warfare. LADAR can detect much more targets than other sensors, such as infrared imaging and radar imaging. Range image and intensity image can be obtained through using LADAR, and they are suitable for automatic target recognition. At present the research of automatic target recognition technology for LADAR is a hot problem. Main work of this paper is composed of three parts: Firstly, current research and application of automatic target recognition technology for LADAR are demonstrated; Secondly, main problems in automatic target recognition for LADAR are thoroughly analyzed, including problems in five stages: preprocessing, target detection, feature extraction, founding pattern database and performance evaluation; Finally, a detailed survey is set forth about technical approach of automatic target recognition for LADAR, including six components: preprocessing, target detection, feature extraction, recognition, modeling and simulation, performance evaluation.
Phase noise in a bidirectional transmission system with polarization maintaining fiber
Yan-Hong Wang, Pan Guo, Guo-Qiang Ni, et al.
At present, bidirectional transmission over a signal fiber is applied in many fields, such as WDM. Bidirectional transmission over a signal fiber can reduce the required number of fibers and uses one optical source, so it is lower cost than unidirectional transmission counterparts. In this paper, the phase-noise counteracting characteristic in the bidirectional transmission over a polarization maintaining fiber (PMF) due to different polarization rotating angle of counter-propagation light is analyzed. The analyzing results indicate that the bidirectional system with a special polarization rotating angle of counter- propagation light has a good property that can counteract phase noises coming from external factors such as temperature etc. reciprocal factors. Thus, phases' fluctuation can be reduced and it has the advantages of measuring phase change and achieving phase calibration. Based on the result, using Jones matrix, the established system is discussed and the phase difference owing to nonreciprocal parameters such as Faraday electromagnetic induction is obtained. So the calibration of phase is achieved according to the measured results.
Aerosol measurements with a combined elastic/non-elastic backscatter lidar in Beijing
Zhenyi Chen, Wenqing Liu, Yujun Zhang, et al.
In order to reach a green Olympics in 2008, an unprecedented environmental experiment jointly launched by the Beijing municipal government and the Chinese Academy of Sciences (CAS) was carried out. AIOFM (Anhui Institute of Optics and Fine Mechanics Experiment) took part in the campaign with an elastic/non-elastic lidar to measure the aerosol distribution and the boundary layer in summer in Beijing. With the combining solution of the Raman lidar and the elastic lidar equation, the important optical parameters of the aerosols (extinction coefficient, backscatter coefficients thus the lidar ratio) were attained. The lidar ratio on July 22 varied from 10sr to 30sr. Since the vertical distribution of the lidar ratio demonstrate different microphysical characteristics in the lower and upper parts of the cloud, so probably the cirrus with the mean lidar ratio of 25sr at the height of 6km can be assumed. On the other hand, a well-mixed boundary layer was observed. Taking into account the effects of the multiple scattering (5%-10%),we obtain a single-scattering optical depth of 0.15.The boundary layer also offered the explanation of the steady ozone concentration measured by the DOAS system at the same position of the observing site.
Development of a nonlinear optical measurement-4f coherent imaging system
Xiaojun Chen, Yinglin Song, Jihua Gu, et al.
After the nonlinear optical phenomena were discovered, people began to research the techniques to detect the optical nonlinearities of materials. In this paper, a new optical nonlinear measurement technique-4f coherent imaging system is recommended. The system has many advantages: single shot real-time measurement, simple experimental apparatus, high sensitivity, being able to detect the magnitude and sign of both nonlinear absorption and refraction at the same time, low requirement of beam spatial distribution, and so on. This paper introduces the theory of the 4f system and makes a detailed review and expounds development and application of the 4f coherent image system. The nerve of the experiment is improving the phase diaphragm. The shape of the diaphragm from the double-slits to the small rectangular object, and transition to a circular aperture, finally forming a circular phase diaphragm, which is a circular aperture in the center add a phase object. Following these diaphragm changes, the sensitivity of the system is greatly improved. The latest developments of the system are series-wound double 4f coherent imaging technique and the time-resolved pump-probe system based on NIT-PO. The time-resolved pump-probe system based on NIT-PO can be used to measure the dynamic characteristics of excited states nonlinear absorption and refraction.
Mode pattern analysis of gallium nitride-based laser diodes
Xiaomin Jin, Sean Jobe, Simeon Trieu, et al.
In this paper, we present an analysis of gallium nitride (GaN) quantum-well (QW) laser diode (LD) by numerical simulation. Here we discuss three aspects that are crucial to our analysis. First, the transverse mode pattern is studied, and our current GaN diode laser structure is discussed with optical waveguide mode analysis. Then we compare the QW design of the laser and maximize laser modal gain. Finally, we report the influence of the electron block (e-block) layer on lasing performance of our design.
Optical technique for reducing excess noise and quantum noise in a heterodyne interferometer
A simple heterodyne interferometer associates with phase to amplitude conversion and amplitude sensitive technique is proposed. The excess noise and the quantum noise introduced by the autocorrelations between sensing beam and local oscillator beam are reduced at suitable phase bias. Meanwhile, the differential phase arises from target displacement is detected by optical differential and optical additive operations. The amplitude and phase quadrature are also achieved simultaneously in proposed interferometer.
Stimulatory effect of low-level GaAlAs laser (808 nm) on bone defect created surgically in rabbit femur
Qiushi Li, Zhou Qu
Recently, low-level laser therapy (LLLT) has been reported to have a photobiomodulation effect on bio-tissues. Our aim was to evaluate the effect of low level GaAlAs laser on bone regeneration around bone defect sites created surgically in rabbit femur. Thirty rabbits were randomly divided into an experimental and a control groups. A GaAlAs semiconductor diode laser was applied in the experimental group( λ = 808nm, P =75mW, (symbol) =0.4mm,t=5min, ρE=28J/cm2)immediately after surgery once a day for 3 consecutive days with no irradiation in the control group. Rabbits were sacrificed on the 7th, 14th, 21th days after surgery (DAS) and femur samples were prepared for bone histomorphometry analysis. The results showed that the bone volume, the osteoid volume, osteoblast surface and the mineral apposition rate in the laser group were higher statistically (P<0.05) than those indices in the control group at different periods. These data revealed that LLLT can enhance bone regeneration. LLLT seems to have a clinical application in promoting bone healing around implant in the future.
Investigation of high-order optical nonlinearities by the Z-scan technique
Guang Shi, Yuxiao Wang, Xueru Zhang, et al.
We demonstrate theoretically and numerically how to identify and separate the high-order absorptive and refractive nonlinearities. We give, for multiphoton absorption, the formulas of the nonlinear imaginary phase shift, and thus the normalized transmittance of open aperture Z-scan. In order to determine the two-photon and three-photon absorptions immediately, we also give two empirical formulas with considerable accuracy, which require only the nonlinear normalized transmittance at the focus. Moreover, we show the Gaussian decomposition method and zeroth-order Hankel transform to obtain the complex optical field at the far-field aperture. We find that the former frequently used fails to describe the propagation process for the large nonlinear imaginary phase shift. The influence of linear transmittance of aperture and the multiphoton absorption on the measurement of nonlinear refractive index are also analyzed in detail. In addition, we show the competition relationship between low-order and high-order optical nonlinearities, depending on the intensities at different z positions.
Optimization of doubly Q-switched lasers with both an electro-optic modulator and a GaAs saturable absorber
Wenjing Tang, Dechun Li, Shengzhi Zhao, et al.
It has been proved theoretically and experimentally that a doubly Q-switched laser with both an electro-optic (EO) modulator and a GaAs saturable absorber can obtain more symmetric and shorter pulse with high pulse peak power, which is more useful in some applications. Therefore it is essential to optimize this kind of doubly Q-switched lasers. In this paper, by combining the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs saturable absorber, and considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the electro-optic (EO) Q-switch, we introduce some new normalized parameters and provide the new normalized rate equations for a diode-pumped doubly Q-switched laser with both an electro-optic (EO) modulator and a GaAs saturable absorber, which are solved numerically. The key parameters of an optimally coupled doubly Q-switched laser are determined, and a group of general curves are generated for the first time. These key parameters include the optimal normalized coupling parameter, the optimal normalized saturable absorber parameters, and the normalized parameters of the electro-optic (EO) Q-switch, which can maximize the output energy. Meanwhile, the corresponding normalized energy, the normalized peak power and the normalized pulse width are given. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the GaAs saturable absorber, the electro-optic (EO) Q-switch, the resonator and the spatial distributions of the intracavity photon density. These optimal results are compared with those of the optimized single Q-switched lasers. Sample calculations for a diode-pumped Nd:YVO4 laser with both an electro-optic (EO) modulator and a GaAs saturable absorber are presented to demonstrate the use of the curves and the relevant formulas.
Study on the characteristics of an Er/Yb co-doped double cladding fiber laser
Zhou Qu, Mingliang Yan
An Er/Yb co-doped double cladding fiber laser pumped at 980 nm was optimized. The double-cladding fiber laser with whole fiber was obtained by end-pumping and utilizing fiber bragg grating as a resonator. The output power of laser was analyzed along the changes of output grating reflectance (L=10m) as well as the fiber length (R2=4%). Consequently, a fiber with 4 m Er / Yb co-doped double cladding was employed as gain medium while a fiber of which the reflectance was approximately 15% was used as output resonator mirror. Thereafter the technical indexes of EYDF(Er / Yb Double cladding Fiber) were measured. The absorption maximum of fiber core Er3+ was higher than 30dB/m and material gain maximum was observed at 1535nm. Moreover, the diameters of fiber core and inner cladding of double-cladding fiber grating were 6μm and 125μm respectively however the diameters of fiber core and inner cladding of Er/Yb co-doped double cladding fiber were 7μm and 130μm separately.According to the experimental data, a fiber laser with 4 m Er / Yb co-doped double cladding and launched maximum pump power of 3.4 W was set up. Proposed laser shows the maximum output power of 1.25 W and slope efficiency of 40%.
Mutual injection phase-locking fiber laser with an extra-cavity based on a corner cube
Yong Cheng, Chaowei Mi, Yang Liu, et al.
Phase locking and coherent beam combination of two individual double-clad fiber lasers by a novel extra-cavity mutual injection-locking method based on a corner-cube are proposed and experimentally demonstrated. Steady interference stripes with high contrast ratio(about 81.7%) are observed. The output power of the phase-locked array exceeded 10W and the power combining efficiency is about 80%. No power-restriction optical components are utilized in our phaselocking experiment and the output power can be further up-scaled.
Simulation on spatial resolution in photoacoustic tomography
Tao Lu, Hui Yong Mao
Photoacoustic tomography(PAT) is a new imaging modality of biological tissues. It merges the contrast advantage of pure optical imaging with the resolution advantage of pure ultrasound imaging. A numerical simulation method of spatial resolution in photoacoustic tomography was studied. The full width at half maximum (FWHM) of point spread function (PSF) was calculated to determine the spatial resolution. The effectiveness of the simulation method was indicated by experiment. The relationship between spatial resolution and filter's cutoff frequency and active detector aperture size was calculated. The result could be used to calculate the spatial resolution of photoacoustic imaging system.
Optimization of the referential laser signal to a Fourier transform spectrometer
Huandong Wei, Jianwen Hua, Zuoxiao Dai, et al.
The vertical atmospheric sounding interferometer is based on the classical Michelson Interferometer mechanics. To keep the uniformity of the speed and the alignment of the movable plane mirror, it introduces the referential optical path. As the metrological standard, it is very important to get high-quality referential signals. Because of the complexity of the interference system, the referential signals will degenerate when arriving at the laser detectors. In this paper, three factors that impact the quality of the referential signals and countermeasures are presented. Firstly because the laser speckle is not ideally proportioned and the laser beam is not ideally vertically reflected by the movable mirror, the laser speckle swings with the movement of the movable mirror, resulting in the fluctuating of the power radiated on the laser detectors. Secondly, when the initial angle between the fixed mirror and the movable mirror is too large, the modulation depth ripples in a large scale with the small misalignment of the movable mirror. Lastly, the light reflected back to the semiconductor laser will engender impact on the light source. By taking countermeasures, usable, accurate enough referential laser signals are finally acquired.
New method for side pumping of double-clad fiber lasers using planar grating written into the inner cladding
Xingchun Chu, Shanghong Zhao, Zhouliang Wu, et al.
A new side pumping method based on the diffractive properties of a planar grating which is directly written into the inner cladding of a double-clad fiber (DCF) is proposed. This technique assumes that the inner cladding of the DCF is highly photosensitive and its diameter is large enough. Then a planar grating with a proper thickness can be written into the inner cladding. The principles, characteristics and coupling efficiencies of the proposed scheme are described and simulated by coupled wave theory. The simulating results show that the coupling efficiencies can achieve over 98% for TE-, TM- and un-polarized incident pump lights simultaneously. And the average coupling efficiencies can still achieve 80% regardless of TE or TM polarization even when the pump wavelength ranges from 974 to 978nm and the incident angle ranges from −0.8° to 0.8°. The fabrication tolerances of the planar grating and the leakage of pump powers for multi-point side-pumping are also analyzed. The advantages of the proposed scheme include: (1) no risk of damaging the DCF; (2) no index-matching optical adhesive; (3) high temperature sustainability; (4) simple, stable and compact. It provides an effective way to scale the output power of DCF lasers or amplifiers to a high level.
A new twelve-quadrant photoelectric detection scheme of eliminating the influence of a jamming spot on laser guidance
Jin-Hua Chai, Ning Liu
A new experimental method is put forward for the influence of two laser spots on the direction deviation in four-quadrant photoelectric detection for laser guidance. The experimental apparatus and findings are given. The results are: in two cases of spot size, the curve of the relative center direction deviation vs. relative intensity difference of two laser spots; the deviation error in each quadrant under the condition of relative intensity difference value less than 2%. It is concluded that smaller relative intensity difference and larger spot size are beneficial to the decrease of the deviation error. Based on the experiments a new scheme of twelve -quadrant photoelectric detection to eliminate the influence of jamming spot on laser guidance is proposed: The twelve -quadrant photoelectric detector is composed of three four-quadrant photoelectric detectors arrayed in left, middle and right side. When a jamming spot appears, its relative position is judged by the circuit. When spots simultaneously appear in two quadrant photoelectric detectors, only the signal of target spot is put into succeeding control circuits, so the influence of jamming spot is eliminated.
Relation research on laser-induced shockwave and laser pulse in laser shock processing
Xia Ye, Yongkang Zhang, Hongbing Yao, et al.
When a short pulse of a Q-switched high-power laser hit surface of materials, laser energy would be absorbed rapidly, thus producing explosive vaporization, and almost at the same time a high-pressure shock wave was induced, called laser shock wave. This ultra-high pressure induced by high power laser had been applied in the fields of basic research and engineering application such as inertial confined fusion, laser shock processing, etc. Influence of variable laser power density on laser shock wave was studied in this paper. Influences of variation of laser wavelength and pulse duration on laser shock waves were also discussed in laser shock processing. Piezoelectric Polyvinylidene Fluoride (PVDF) transducer and TDS3052B Digital Oscilloscope were applied in our experiments to measure the piezoelectric wave of PVDF and the corresponding stress wave induced by laser in real time. Differences and relations between laser-induced shockwave and laser pulse in laser shock processing were researched according to the obtained waves, and the detailed analyses of their causes were given based on the formation of laser-induced shock wave. The research results could have important implications for a better understanding of characteristics of laser shock wave and further studies into the interaction between high-power laser and materials.
Simulation of high precision pulsed laser fuze based on phase shifting
Huimin Chen, Ping Li, Zhoufeng Peng, et al.
With the development of semiconductor laser technology, laser proximity fuzes have been widely used in various kinds of guided missiles and routine ammunitions. And its precision of ranging has a direct influence on the overall performance of the system. This work employed Spartan III series FPGA chip from Xilinx company. Through phase shifting the primary reference clock and ranging with four doubled-frequency clocks with each phase shiftings of 90 degree, the ranging precision can be improved obviously. The theoretical ranging error is 0.1875m and the result has been proven by simulation with Modelsim. Valuable conclusions were drawn for improving the ranging precision of laser fuze.
Echo broadening effect in the range-gated active imaging technique
Xinwei Wang, Yan Zhou, Songtao Fan, et al.
We have presented the Echo Broadening Effect of range-gated active imaging. It can respectively generate a head signal part and a tail signal part both sides of the echo signal profile. Our research demonstrates that the head signal and the tail signal impact the depth of view, detection range and imaging quality, especially the head signal. In order to solve the problems, we establish a model of the echo broadening effect, and analyze the signal energy characteristics and atmospheric backscatter. We have given the depth of view under the effect, verified it in experiment, and found that the reasonable choosing of the illuminator laser pulse time and the camera gate time can mange the effect to optimize range-gated imaging systems.
Analysis of characteristics of blue-green laser propagation through ocean water
Xiao-li Yang, Hong Yang, Li-ming Xu, et al.
The optical channel models for airborne submarine laser communication are built and the received energy is discussed. In this propagation channel, sea has the most important impact on the power attenuation. Applying the classical electron scattering theory to the photo scattering effects in the sea, the transmission delay of underwater laser pulse is investigated by small-angle approximation theory, caused by the scattering effects in the sea. To indicate the influences of the seawater properties on the transmission delay, some interrelated curves are displayed. The multi-path time spreading of signal pulse is studied. The waveform of received signals in receiver in submarine laser communication system is analyzed and simulated by use of Monte Carlo simulation. The results deduced by using Monte Carlo coincide with that simulated by using small-angle approximation theory.
The study on nonlinear bifurcation dynamics of a semiconductor ring laser
Bin Zhang, Lu-Hong Mao, Sheng Xie, et al.
Based on dynamics models of the electronic bi-stable behavior in a semiconductor ring laser and using the methods of the modern nonlinear dynamics, the stability and bifuraction behavior in a semiconductor ring laser are analyzed and calculated in this paper. The calculated results show that the ring laser can undergoes the Hopf bifurcation by changing pump parameters which can lead the complex nonlinear movement such as limit cycle and Chaos. The effects of backscatter parameters on the operation regions are also calculated The calculated results show that the change of backscatter parameter can result different dynamics behaviors including bifurcation. At last the theoretical result is compared with experiment. The device process and structure is described and the experiment result agree with our theory.
Open-loop Sagnac optical fiber sensor for detecting acoustic emission
Yijun Liang, Ming Wang, Junfeng Liu, et al.
A novel open loop Sagnac optical fiber sensing system for detecting AE(acoustic emission) has been proposed and demonstrated. The fiber loop of the Sagnac interferometer was cut off and formed two fiber ports, they were bound and made into the fiber probe. It was placed in the front of the reflector attached to the measured solid. The light from one port was reflected by the reflector and injected into the other fiber port. On the basis of the output optical field distribution function, the position of maximum reflected light intensity was theoretically analyzed. The best work region between the fiber probe and the reflector was ascertained by the experiment. Phase modulation property of the optical fiber sensor was discussed and the optimal working state was obtained by the computer simulation. The optical phase was modulated by the vibration of the reflector generated by the AE. The AE signals were obtained though the optoelectronic conversion, and the frequency of the AE were acquired by using Fourier transform. The experiment results show that the system could be used to detect the ultrasonic waves that propagating on the surface of the solid. The open loop Sagnac optical fiber interferometer sensor has potential for the structural integrity monitoring and NDT applications.
Research on the hollow double-half Gaussian laser beams of long distance detection source
Yuan Dong, Xi-He Zhang, Liang Chen, et al.
In this paper, a new kind of long distance detection source-- hollow double-half Gaussian laser beams is put forward. By use of modified Cassegrain optics system, we obtained hollow beams with special light distribution-parallel hollow double-half Gaussian laser beams, the intensity distribution of this kind of hollow beams is zero at all the hollow area and is maximum at inner margin, so forms double half-Gaussian beams, and the inner and the outer diameters of the hollow beams are controllable. The analytical equation of propagation and transformation of the hollow laser beams in free space was deduced. The simulation shows that the intensity exhibits three-dimensional trap distribution in the near-field, while the double half-Gaussian hollow beams turns into solid laser beams when propagating a certain distance, which shows the characteristic of self-focus. By use of the characteristic of self-focus of the double half-Gaussian hollow beams, we can realized the self-gating long distance detection to the small object even if in the condition of lower laser power. The technology will be applied broadly in the near years.
The endpoint detection technique for deep submicrometer plasma etching
Wei Wang, Zhi-yun Du, Yong Zeng, et al.
The availability of reliable optical sensor technology provides opportunities to better characterize and control plasma etching processes in real time, they could play a important role in endpoint detection, fault diagnostics and processes feedback control and so on. The optical emission spectroscopy (OES) method becomes deficient in the case of deep submicrometer gate etching. In the newly developed high density inductively coupled plasma (HD-ICP) etching system, Interferometry endpoint (IEP) is introduced to get the EPD. The IEP fringe count algorithm is investigated to predict the end point, and then its signal is used to control etching rate and to call end point with OES signal in over etching (OE) processes step. The experiment results show that IEP together with OES provide extra process control margin for advanced device with thinner gate oxide.
Numerical simulation of air-breathing mode laser propulsion by nanosecond laser pulse
Lei Shi, Shanghong Zhao, Xingchun Chu, et al.
Based on Navier-Stokes equations, numerical simulations of air-breathing mode laser propulsion by nanosecond laser pulse are carried out. An analytical model of the thruster's inner flow involving the simple processing of the ignition zone is established. The evolvement of the laser sustained plasma shockwaves is systemic analyzed; also the effects of pulse energy and thruster's structure such as focal length, scale and open angle on propulsion performance are researched. The simulated results show that the focal length dominates among the structural factors of thruster in the propulsion by nanosecond laser pulse. The larger focal length leads to better propulsion performance. It is also evident that for single pulse propulsion, nanosecond laser pulse is better than microsecond laser pulse, the momentum coupling efficient achieved by the former is 2~5 times of the latter's, which is highly agree with the existing experimental results.
Conversion efficiency analysis of frequency-doubling in the form of Cerenkov configuration based on ion-implanted lithium niobate planar waveguide
Guolong Du, Guiqiu Li, Shengzhi Zhao, et al.
Optical second-harmonic generation (SHG) in the form of Cerenkov radiation is analyzed by directly resolving the wave equations. A simple general solution has been obtained which expresses the SHG efficiency in terms of waveguide parameters. Numerical examples are plotted for ion-implanted Lithium Niobate (LiNbO3) planar waveguide. Keywords: LiNbO3, TM mode, Cerenkov SHG, ion-implantation, planar waveguide.
Evaluation of near-infrared laser Raman spectroscopy underwater research
Jinjia Guo, Bin Zhang, Jianglai Wu, et al.
The in-situ chemical detection in deep sea is very important for mineral resources exploitation. Laser Raman Spectroscopy as a powerful tool for chemical analysis has been used in deep sea detection recently. It was found that the fluorescence always exists as the background on Raman spectra detecting in ocean. It is apparent that the fluorescence background could be decrease effectively using near infrared wavelength as excitation source. While near infrared laser has few application underwater due to the absorption of water in this wavelength range. In this paper, a 785nm Raman spectrometer was used to evaluate the near infrared laser Raman spectroscopy for underwater application. It was found that the Raman shift of SO4 2- at 981cm-1 can be easily detected from Qingdao near shore sea water samples without sever fluorescence background. With mixed solution of SO4 2- and HCO3 -, the detection limit achieved for SO4 2- at 981cm-1 and HCO3 - at 1017cm-1 was obtained by 785nm compact Raman spectrometer to be 0.00625mol/l and 0.025mol/l with 10s integration time respectively. The obtained results proved the feasibility of near infrared laser Raman underwater detection.
The research of a novel single mirror 2D laser scanner
Si-hua Xiang, Peng Wang, Si-hai Chen, et al.
A single mirror 2D laser scanner is designed, produced and tested in the paper. The mirror of the scanner is suspended on a compact cross blade flexure and driven by four voice coil actuators. The voice coil actuators designed specially can output strong driving force and have sufficient large gap for mirror's deflection. An in-house ingenious deflection angle detecting system based on a 2D position sensitive detector provides feedback to enable two-axis closed-loop scanning. Details of the voice coil actuators design, the mechanical structure design and deflection angle detecting system as well as the control-loop implementation are described. Test results shows that the mechanical deflection angles in both azimuth and elevation are about ±5°, and the closed-loop bandwidth is 350Hz. The diameter of the mirror is 40mm, and the diameter of laser beam can reach 35mm when mechanical scanning angle is 5°. A 2D scanning is realized by the scanner deflecting in two orthogonal axes. The vertical scanning frequency is 10Hz, and the scanning wave is triangle wave. At the same time, the horizontal scanning frequency is 80Hz, and the scanning wave is sine wave.
The study of blue LED to induce fluorescence spectroscopy and fluorescence imaging for oral carcinoma detection
Longjiang Zheng, Yuanting Hu
Fluorescence spectroscopy and fluorescence imaging diagnosis of malignant lesions provides us with a new method to diagnose diseases in precancerous stage. Early diagnosis of disease has significant importance in cancer treatment, because most cancers can be cured well in precancerous, especially when the diffusion of cancer is limited in a restricted region. In this study, Golden hamster models were applied to 5% 9, 10 dimethyl-1, 2-benzanthracene (DMBA) to induce hamster buccal cheek pouch carcinoma three times a week. Rose Bengal, which has been used in clinican for years and avoids visible side-effect to human was chosen as photosensitizer. 405 nm blue LED was used to induce the fluorescence of photosensitizer. After topical application of photosensitizer, characteristic red emission fluorescence peak was observed around 600nm. Similar, normal oral cavity has special luminescence around 480nm. Fluorescence spectroscopy technology is based on analysing emission peaks of photosensitizer in the areas of oral carcinoma, moreover, red-to-green (IR/IG) intensity ratio is also applied as a diagnostic algorithm. A CCD which is connected with a computer is used to take pictures at carcinoma areas through different filters. Fluorescence images from normal hamster buccal cheek pouch are compared with those from carcinogen-induced models of carcinoma, and morphological differences between normal and lesion tissue can be distinguished. The pictures are analyzed by Matlab and shown on the screen of computer. This paper demonstrates that Rose Bengal could be used as photosensitizer to detect oral carcinoma, and blue LED as excitation source could not only have a good effect to diagnose oral carcinoma, but also decrease cost greatly.
Image watermarking algorithm applied to free space optical communication
Jing-feng Zang, Fu-chang Yin, Zhi-qi Lin
The AGWN model, based on the atmospheric attenuation and turbulence effect is present. In the paper, a robust image watermark technology is proposed based on extended set partitioning in hierarchical trees algorithm (ESPIHT) and low density Parity check codes (LDPC). The Watermarking Algorithm is applied in the free space optical communication (FSO) by Joint Source-Channel Coding (JSCC), and simulated in BPSK modulation over AWGN channel and different level error correction channel coding. The results of simulation show that the presented algorithm is effective and robust to common image processing operations and some distortions such as cropping, pinching, pixel-shifting and so on. And it has strong error correction performance in burst errors and random errors, so it is appropriate for complicated environment of FSO.
An improved method of new image decomposition technique: two-dimensional EMD
Wei-jiang Zhao, He-yong Zhang, De-ming Ren, et al.
An improved algorithm of 2-D Empirical Mode Decomposition (EMD) in image processing has been presented. It contains selecting extrema of the pixels and interpolation of them in the course of EMD, A variance phenomenon has been discovered in the interpolation of boundary pixels. Delaunay Triangulation has been used to partition the selected extrema, a pixel that not contained in the Delaunay polygon can be processed through symmetry principle, It can restrain the variance phenomenon that appeared in the cubic spline interpolation. An image has been processed with the improved algorithm, The calculation result of standard deviation between the original image and the reconstructed image is 6.667×10-6 . A slight fluctuation can be seen from the calculation result. The reconstructed image is consistent with the original image. It demonstrates that the improved algorithm been presented is accurate and feasible. The method of EMD is used in image compression and de-noising more and more popular, therefore, the improved algorithm in the paper will be useful in the course of calculation speed enhancement of image processing based on EMD.
The study of absolute distance measurement based on the self-mixing interference in laser diode
Ting-ting Wang, Chuang Zhang
In this work, an absolute distance measurement method based on the self-mixing interference is presented. The principles of the method used three-mirror cavity equivalent model are studied in this paper, and the mathematical model is given. Wavelength modulation of the laser beam is obtained by saw-tooth modulating the infection current of the laser diode. Absolute distance of the external target is determined by Fourier analysis method. The frequency of signal from PD is linearly dependent on absolute distance, but also affected by temperature and fluctuation of current source. A dual-path method which uses the reference technique for absolute distance measurement has been proposed. The theoretical analysis shows that the method can eliminate errors resulting from distance-independent variations in the setup. Accuracy and stability can be improved. Simulated results show that a resolution of ±0.2mm can be achieved for absolute distance ranging from 250mm to 500mm. In the same measurement range, the resolution we obtained is better than other absolute distance measurement system proposed base on self-mixing interference.
LD side-pumped Nd:YAG Q-switched laser without water cooling
Ming Ling, Guang-yong Jin, Xue-chun Tan, et al.
A novel LD side-pumped Nd:YAG Q-switched solid-state laser, which made use of the special pumping strcture with conductive cooling instead of water cooling, was investigated.After selecting an appropriate length and diameter of Nd:YAG laser crystal rod and using three groups of laser diode centimeter bar which was composed by 12 laser diodes and uniformly arranged according to the angle of 120°,side-pumping structure of laser was accomplished.Adopting plano-concave resonator ,mending double end face of laser crystal and designing heat-stability resonator made the resonator steadily oscillate.Laser crystal rod which was tight fastened by copper net was conductively cooled and radiation block was furnished on the external of copper net for increasing the radiation capacity.High reflection gold film was plated on the cooling wall in the opposite way of pumping light, so that the laser crystal was uniformly pumped and the laser with low order mode output.Making the use of pillar lens focus and ray trace computing, reasonable parameters were caculated to couple pumping light to laser with high-efficiency.It was the electrooptic Q-switched which was made to be micro-integration eliminating voltage by KD*P crystal that improved the ratio between acting and unacting.Inner heat radiated from laser in good time with TE cooler and the laser ran at constant temperature with water cooling when the big external heat sink emanated a steady heat to periphery. Experiments revealed that the syetem pumping efficiency riseed by 18% and the laser threshold energy was 192 mJ under the condition of this novel pumping structure. The low mode output of 10~12ns pulse width and the maximum output energy of 98 mJ was achieved with an incident pump energy of 720 mJ in 1064nm.The optical-to-optical conversion efficiency was up to 13. 6 %,and the power instability in 24 h was better than ±1. 7 %.
The high accuracy data processing system of laser interferometry signals based on MSP430
Yong-yue Qi, Yu-chi Lin, Mei-rong Zhao
Generally speaking there are two orthogonal signals used in single-frequency laser interferometer for differentiating direction and electronic subdivision. However there usually exist three errors with the interferential signals: zero offsets error, unequal amplitude error and quadrature phase shift error. These three errors have a serious impact on subdivision precision. Based on Heydemann error compensation algorithm, it is proposed to achieve compensation of the three errors. Due to complicated operation of the Heydemann mode, a improved arithmetic is advanced to decrease the calculating time effectively in accordance with the special characteristic that only one item of data will be changed in each fitting algorithm operation. Then a real-time and dynamic compensatory circuit is designed. Taking microchip MSP430 as the core of hardware system, two input signals with the three errors are turned into digital quantity by the AD7862. After data processing in line with improved arithmetic, two ideal signals without errors are output by the AD7225. At the same time two original signals are turned into relevant square wave and imported to the differentiating direction circuit. The impulse exported from the distinguishing direction circuit is counted by the timer of the microchip. According to the number of the pulse and the soft subdivision the final result is showed by LED. The arithmetic and the circuit are adopted to test the capability of a laser interferometer with 8 times optical path difference and the measuring accuracy of 12-14nm is achieved.
Laboratory experiments on synthetic-aperture laser radar with acousto-optic modulators
HuanHuan Liu, XiaoDong Zeng, ChangQing Cao, et al.
The diffraction limit of laser is smaller than microwave's for its shorter wavelength. Higher spatial resolution will be achieved when laser is applied to the synthetic-aperture radar, called synthetic-aperture laser radar (SAL). Just because of many advantages, in recent years the research on SAL is becoming a hotspot. One of key techniques of SAL is heterodyne detection of signals by means of linear frequency modulation pulse compression (LFM-PC); this paper introduces an experiment based on heterodyne detection with an acousto-optic frequency shifter (AOFS) in our laboratory. Detailed discussion about AOFS is presented. We find that the acousto-optic modulator can considerably influence the transmitted light beam. In particular, when the width of laser beam is larger than the effective width of acousto-optic cell, the transverse distribution of scattering light intensity is inhomogeneous, which will decrease the signal-to-noise ratio of the heterodyne detection. This paper discusses the coupled partial difference equations
Weak signal detection technology for synthetic aperture ladar
Li-li Wang, Xiao-dong Zeng, Zhe-jun Feng, et al.
When remote objects are detected by use of SAL, weak echo signal is easy to be interfered by noises. To obtain high receiving performance, the amplifier and signal processing system should be carefully designed. In this paper, the circuit consisting of the microwave filter, the pre-amplifier and the main amplier is designed under the condition of photodiode impedance matching. The major noises of PIN photo diode are analyzed and a low noise pre-amplifier circuit is designed,which can improve the signal to noise ratio ( SNR ) effectively. The noises are filtered by a microwave filter. The circuit self-excited owing to high frequency operating is also taken into account. Some measures that the device is reasonably selected and the circuit is legitimately designed are implemented. The anti-interference of the circuit and the ability of restraining self-excited are improved by shielding box etc. Experimental results indicate that the receiving circuit has small volume and high reliability with high performance.
Research on inverse synthetic aperture ladar
Xiaoyan Zhao, Xiaodong Zeng, Changqing Cao, et al.
Heterodyne detection based on the inverse synthetic aperture ladar (ISAL) can obtain useful information such as phase and amplitude and frequency of the moving target. Through analysis of these information, we can conclude the exact appearance, orientation and other characteristic about the target. However, the heterodyne detection is usually difficult to accomplish. The difficulties lie in two main aspects: the first one is that the wavefront of returned signal wave and local-oscillator wave are misaligned. The second one is that the random phase delay of the returned wave. In this paper, we analyze systematically the principle and effect of heterodyne detection such as separation angle and spot size. Then a useful conclusion is presented to state the exist problem about match between signal wave and local-oscillator field.
Research of the atmosphere propagation characteristics of solar-blind ultraviolet communication
Junhong Chen, Xiaoli Yang
Solar-Blind Ultraviolet Optics Communication is a new type of communication system in atmosphere optics communication fields. Its excellent performances such as safety, 24-hour service, anti-interference, non-line-of-sight, make it different from infrared optics communication. Hence, the solar-blind ultraviolet optics communication gratified the need of special and confidential communication in army. The atmosphere propagation characteristics of the solar-blind ultraviolet is still a difficulty of the communication system. In order to solve this problem, this paper majored on the influences of the solar-blind ultraviolet propagation by the absorption of ozone, the scattering of atmospheric molecule and aerosol.
Atmospheric ammonia monitoring near Beijing National Stadium from July to October in 2008 by open-path TDLAS system
Ying He, Yujun Zhang, Wenqing Liu, et al.
Gaseous ammonia is the most abundant alkaline trace gas in the atmosphere. As ammonia plays an important role in acid deposition and aerosol formation, it influences the regional air quality and atmospheric visibility. TDLAS (Tunable Diode Laser Absorption Spectroscopy)is a method to obtain the spectroscopy of single molecule absorption line in the characteristic absorption spectrum region as the characteristic of the distributed feed back (DFB) diode laser with narrow linewidth and tunability, which makes it possible to detect trace-gas qualitatively or quantificationally. The NH3 in-situ monitoring instrument based on TDLAS and long open path technology have been developed combining with wavelength modulation and harmonic detection techniques to obtain the necessary detection sensitivity. This instrument has been used to measure atmospheric NH3 concentration at an urban site near Beijing National Stadium from July to October in 2008, especially in the period of Beijing Olympics and Paralympics. The continuously monitoring results show that the atmospheric NH3 concentration variation has an obvious diurnal periodicity in the urban of Beijing. First of all, the general diurnal variation rule is the concentration decreased to the minimum in the daytime, and then increased to the maximum at night. Moreover, the NH3 peak concentration decreased obviously at the beginning of the Beijing Olympics then it kept descending during the Paralympics. The obtained maximum of NH3 is between 20.31μg/m3~ 48.54μg/m3 with the daily average concentration between 12.6μg/m3~27.5μg/m3. During these three months, Air Quality Assurance Scheme for the Olympics (AQASO) was implemented through the joint actions of Beijing Municipal Government and the five neighboring provinces/municipalities in north China. The measures such as auto restriction and plant ejection-decreasing are carried out in Beijing. In conclusion, the open-path TDLAS instrument is suitable for atmospheric trace gases detection on-line with its high resolution, high sensitivity, rapid response time without gas sampling. Also correlation studies have verified the positive effects of measures taken for improving the air quality including restricting ammonia formation.
Theoretic analysis on the maximum measurable velocity of a self-mixing laser diode velocimeter
Zhao-yun Zhang, Yang Gao, Xing-hai Zhao, et al.
Laser output power and frequency are modulated when the optical beam is back-scattered into the active cavity. By signal processing, the Doppler frequency can be acquired, and the target's velocity can be calculated. Based on these properties, an interferometry velocity sensor can be designed. In order to know whether the self-mixing laser diode velocimeter is suitable for high speed (km/s) scene, the self-mixing laser diode velocimeter's maximum measurable velocity (MMV) is analyzed. Based on the three-mirror cavity model, relations of the laser output power's frequency fluctuations and Doppler frequency are acquired. External optical feedback is regarded as laser's small-signal modulation by the Doppler frequency. From rate equations of the carrier density and the photon density, following conclusions is acquired: self-mixing laser diode velocimeter's MMV is restricted by laser's relaxation resonant frequency in principle; self-mixing laser diode velocimeter's MMV goes up to kilometers per second theoretically. The result is available to use the self-mixing technique to develop high performance, small overall dimensions and low cast instruments to measure high speed.
Influence of materials' property of laser crystal on thermal effects in high-power DPL
Qin Dai, Xin-zhong Li, Ri-na Wu, et al.
The physical property parameters of laser crystal in solid state lasers vary strongly with temperature, which will intensely affect the thermal effects of high power LD pumping solid state laser (DPL). In this study, by correcting the intensity distribution of the laser beam emitted from the pumping source of laser diodes, a heat transmission model for the laser crystal of a side-pumping geometry with a triangle uniform distribution was established. The temperature and stress distribution are calculated and compared using finite element method under two different conditions, which thermal conductivity, heat capacity and coefficient of thermal expansion of the laser crystal media vary with the temperature, and these physical property parameters are constant. The results show that temperature at the center of laser crystal media will further increase, and there will produce an additional stress except for thermal stress due to the temperature gradient at the radial direction in the laser crystal, which result in more serious thermal effects. This study provides a more visual and accurate reference model for the design and optimization of high power laser diode side pumped solid state lasers.
Study of cooperative effect radiation loss of solid laser
Gui-cai Song, Wei Quan, Dong Seng Guo
Cooperative effect radiation loss of optical pump solid laser was investigated deeply. Using Maxwell-Bloch equation the characteristic and cause of coherent spontaneous were discussed .By laser rate equation, the expression of upper energy level lifetime shortening due to the cooperative effect radiation was given. The influence of cooperative effect for laser threshold and the loss were analyzed. Through the experiment, the relation of coherent spontaneous radiation intensity and direction with reversal population and the power of optical pump was obtained.
Reach on laser imaging technology to terminal guidance
Xue-chun Tan, Guang-yong Jin, Zhi-chao Wu, et al.
The development of range-imaging devices is motivated by various ground and space applications. Tasks in space missions include docking, rendezvous, manipulating robotic arms, landing and autonomous rover applications, sample identification and surface mapping. The ground applications include the guidance of vehicles, robotic and manipulator arms, and other autonomous or teleoperated machines, as well as surface or construction model generation. Without the scanner devices, scannerless imaging lidars have the characteristic of high frame rate, wide field of view and high reliability,which can be successful used in terminal guidance. Diode pumped laser radar with high repetition rate is studied in this paper. A bistatic system is set up and a high speed signal processor for the system is researched. In a conceptual sense, the imaging lidar has two parts, a transmitter and a receiver. Their field of views overlap throughout the measuring range.The imaging lidar operates as follows. Based on principle of pulsed time-of-flight (TOF) laser range finding, the solid-state laser diode-pumped laser produces short laser pulses, which though the expanded lens, then reach the target. The back reflected light is collected with a receiver lens and fed through optical fibres to discrete avalanche photo diodes (APDs). When a received pulse is detected by the comparator a time to digital converter (TDC) stops counting and a time interval, corresponding to the range, is produced. The precision of a single measurement is about ±4.0cm, but better precision is achieved by averaging. Information about the reflectivity of the target is gathered by recording the amplitude of the received pulse. Range images with the lidar prototype were taken indoors, the measuring distance was about 14m.
Beam cleanup experiments for solid state laser with stochastic parallel gradient descent method
Sanhong Wang, Yonghui Liang, Qifeng Yu, et al.
Thermal aberrations in high-power solid-state lasers degrade the beam quality and cause diffraction losses that reduce the output power. Adaptive optics system can be used to compensate for the wavefront distortions in real time to clean up the beam. But the conventional adaptive optics system based on wavefront sensing can't work well with the high-power laser beam cleanup because of the presence of branch points in the phase and the amplitude scintillation. However the other kind of adaptive optics system based on model-free optimization of a scalar beam-quality metric provides an attractive approach to perform the beam cleanup in smaller packages. Such an adaptive optics system with iteration rate of 100 Hz was built up. In this system a stochastic parallel gradient descent (SPGD) algorithm is implemented in a computer to control a deformable mirror for wavefront correction. Beam cleanup experiments with the SPGD AO system were conducted. The high-power laser beam was simulated by transmitting a low-power high-quality laser beam through an Nd: YAG-crystal power amplifier. The thermal aberrations of the beam could be changed by adjusting the pumping current of the power amplifier. The experimental results on the convergence and stability of this adaptive system for various conditions of dynamic aberrations are presented.
Airborne Doppler lidar at 532nm based on a tunable dual-channel Fabry-Perot interferometer
Jian-mei Feng, Ting-wen Xing, Wi-mei Lin
The aim of this paper is to explore a high-precision, a wide range of a frequency discrimination technique, and to study the application of this technique in the optical air data system (MOADS). To overcome the traditional equipment's shortcomings of short velocity detecting range such as pilot static tubes and wind wane, this technique can provide precision aviation data for various aerocrafts , without influencing pneumatic shape and performance of aerocraft. A tunable dual channel Fabry-Perot interferometer is used as a frequency discriminator in an airborne wind lidar system. This new frequency discriminator has been proposed to overcome the exiting frequency discriminator shortcoming. By adjusting the cavity length of interferometer, the speed of aerocraft can be detected and cut into several dynamic range. By this way, the Doppler wind lidar system can detect atmospheric parameters at the meantime, such as speed of aerocraft and temperature of atmosphere around the aerocraft, by analyzing the information of Rayleigh backscattering light. There are three main contribution in this paper: the first is discussing the basic theory of MOADS, calculational method and mathematic model of relative wind velocity between aircraft and wind are put forward.; the second is the parameter optimization of the dual-channel Fabry-Perot interferometer and the structure design of the interferometer; the third is the simulation of the performance and the accuracy of this system. Theory analysis and simulation results show this method is reasonable and practical.
Estimating spectral reflectance in a spectral imaging system
Peng Chen, Tianyu Xie
The identification of tumor is important for the diagnosis of early cancer. Optical reflectance spectrum of human tissue could reveal the characteristics of the tissue that helps medical diagnosis. Multispectral imaging techniques have been widely used for the application of digital recording. In this article we developed a multispectral imaging system with a monochrome CCD, five optical filters including conventional RGB filters and two narrow band filters, light source and imaging processor. We propose a method to reconstruct the reflectance spectrum using a selective combination of spectral estimation technique. With the reconstructed spectrum, we can form the image of the object in certain wavelength that is not in the range of any of the wavelengths corresponding to the above filters. The imaging constructing speed of multispectral imaging system is limited by CCD speed. In order to reconstruct the reflectance spectrum in real-time, the number of the filters involved in the reconstruction should be as less as possible. In the experiment, we investigate the relationship between the number of the filter channels and the estimation error (RMSE).. To minimize the estimation error, we use Weiner estimation to choose the best combination of filter channels for certain wavelength. Using the proposed method, we can achieve high accuracy of image reconstruction with limited number of filter channels in real time. In this paper, the multispectral imaging system setup is briefly introduced, and the method of reconstructing the reflectance spectrum is described.
Determination of metals in liquid by laser-induced breakdown spectroscopy
Zhaoxiang Lin, Liang Chang, Jie Li, et al.
This paper reports studies on metals in the liquid by laser-induced breakdown spectroscopy in order to detection of heavy metals in industrial wastewater. A measuring device by LIBS has been established which including the Nd:YAG laser, Echelle spectrograph, intensified charge-coupled device (ICCD) and liquid jet. The characteristic spectral lines of twelve metals in actual industrial wastewater from a certain nonferrous metals company were analyzed using LIBS. The calibration curves of the metals in liquid were acquired by the experiment and the linear correlation coefficients were high. The detection limits of metals obtained from the liquid were low, especially for the Ca, Cu, K, Mg, Mn and Na. The results show that the measuring system can be applied in the on-line, rapid detection of heavy metals in industrial wastewater, and it has wide range of applications.
Research on atmospheric turbulence's influence on active laser reconnaissance
Xian-an Dou, Chuang-xin Zhang, Xiao-quan Sun, et al.
In order to study the atmospheric turbulence's influence on active laser reconnaissance, a theoretical model of cat-eye system illuminated by Gaussian-beam which propagates through atmospheric turbulence over a long distance was constructed. The mean irradiance and the scintillation index were calculated under the Rytov approximation. The theoretical analysis and numerical simulation results indicate that the mean irradiance and scintillation index of the active laser reconnaissance echo influenced by atmospheric turbulence are both increased near the optical axis. Experiment was carried out to validate the theoretical analysis results and the experimental results are shown to be in good agreement with the theoretical predictions.
A sensitive solid-phase time-resolved fluorescence immunoassay apparatus
Yun-lei Wang, Ke-fei Song, Wei-lai Zhang, et al.
In the device, a He-Ne laser of flash frequency 1-20 Hz was adopted as exciting light source, and three key technical problems have been solved successfully in order to enhance the detecting sensitivity and measuring stability of the device for time-resolved fluorimmunoassays(TRFIA)[1]. The first one is to design optimum exciting optical system, so that the exciting light beam excite the sample most effectively. The second one is to have a project spectrum filter which can reduce the affection of the background light to the photomultiplier tube and also ensure influence of the stray light and mixed diffusion light to the sample fluorescence to the least, the sample fluorescence through the integrating sphere and come to the grating monochromator, The right wavelength will be chosed through changing the angle of incidence of the grating monochromator. The third one is to simulate the principle of sample averaging of BOXCAR averager. In the device, SCM was used as primary controller and CPLD was used as timing controller. Through the preparation process, signal-to-noise ratio(SNR) will be improved, also adjust delay time, ampling frequency and sampling number arbitrarily. By testing, the sensitivity is 10-12mol/L(substance marked by Eu3+), examination repeat is ≤2.5%, examination linearity is from 10-8mol/L to 10-12mol/L, correlation coefficient is 99.98%(p≤0.01). The instrument is advanced for ultrasensitive detection of antigen and antibody , and solve the tumor, genetic variation, the virus protein detection.
Study of the hollow conical laser and its application
Gui-cai Song, Wei Quan
Based on the theory of the conical refraction, the hollow conical laser will appear at the internal of the biaxial crystal when laser traveling along one of the axis of the biaxial crystal. The hollow conical laser is different from the solid laser; all of its energy is disturbing on the cone that is similarly the funnel. The study of the produce and control of the hollow conical laser will provide the theoretical and technique basis for its application. In this paper, Based on the matter equation of anisotropies and the propagation law of light in the biaxial crystal, the production of the conical laser was theoretically analyzed and calculated in detail, and the cone angle equation of the hollow conical refraction was obtained, which provided the control and modulation of hollow conical laser with theoretical bases. The cone angle of the conical laser was adjusted by changing the convergence angle of the incidence laser; the all-beam, large-angle and dynamic laser scan was realized by controlling emergent conical laser with varifocal system.
Spectral switches of the off-axis Gaussian beams
Yongping Huang, Guangpu Zhao
The study of the spectral switches has been extended to the off-axis regime within the framework of the paraxial approximation, and the main attention is focused on the influence of the off-axis parameters and incident angles on the behavior of the spectral switches. It is shown the critical position uc, spectral minimum Smin and transition height Δ of the spectral switch depend on the off-axis parameters Δu and incident angles φ. By a suitable choice of system parameters, Smin, Δ and zc of the spectral switch can be variable. Therefore, this kind of spectral changes might find some interesting applications in spectrum-selective interconnects. The on-axis Gaussian beams are treated as a special case of the general result. Keywords: modern optics, aperture diffraction, spectral switch, off-axis Gaussian beam
Polarization characteristic of laser backscattering from randomly rough surfaces
Xiping Cai, Yanshan Chen, Lei Chen, et al.
The polarization characteristic of laser backscattering from randomly rough surfaces is studied theoretically and experimentally in this paper. The effect of multiple scattering from rough surfaces is analyzed. The equation for the backscattering coefficient and the polarization of Gaussian rough surfaces are derived and the simulation is conducted under several certain conditions. The polarization characteristics of different materials with different shapes are measured. The experimental results and the simulated numerical values are compared and analyzed in detail.
Analyzing of frequency doubling conversion efficiency on 266nm ultraviolet laser
Chao Wang, Guangyong Jin, Yongji Yu, et al.
In this paper, the impact of factors on frequency conversion efficiency has analyzed departing from the theoretical formula of frequency doubling frequency efficiency. The results of analyzing show that the frequency multiplication efficiency closely to be not only related to the fundamental frequency laser parameter, but also influenced by several factors such as crystal type, crystal length and so forth. Because of the needs of high conversion efficiency of doubling frequency, the fundamental frequency laser parameter, the crystal type and the crystal length must be determined reasonably to achieve the optimum parameter between fundamental wave peak power density and phase mismatch factor. To compare with the conclusion mentioned above, an experimental device was established on 266nm quadrupler UV laser and 10mJ UV laser which quadruple conversion efficiency 15.5% was achieved in the condition of fundamental frequency single pulse energy 60mJ, the divergence angle under the beam quality M 2=2, pulse width 10ns.
The measurement of the H2S in the pre-desulfurization of natural gas in the Shengli oil field with the TDL
Xiao-wen Shu, Yu-jun Zhang, Dian-qiang Yu, et al.
Hydrogen Sulfide, with the character of erosion and strong toxicity, is a kind of associated gas of nature gas. How to measure and monitor the hydrogen sulfide concentration becomes an important issue to be solved in nature gas transfer-process. Online measurement for the hydrogen sulfide concentration before the desulphurization remains very difficult in Bonan gas gathering station of SINOPEC Shengli Oil Field (SOF).TDL(Tunable Diode Laser) can relative easily select the absorption line of the detecting gas without the interference from other gas thus make the rapid and accurate hydrogen sulfide measurement a possible. In this paper, a hydrogen sulfide measurement system is designed and then be carried out in Bonan gas gathering station of (SOF) .The implemented experiments showed the system effectively solved some problems such as overfall, temperature and pressure. After comparing the hydrogen sulfide online detection sensor of the TDLAS industry with the long hydrogen sulfide detection tube, the linear fitted relationship with the correlation coefficient of 99.96% between them was attained. In order to meet the requests of industrial field anti-explosion, the open-path optical coupling technology was performed in china for the first time. All the results demonstrate that the system will be put into use and enjoy a high application in the near future.
The research of laser off-axis scattering measurement technology based stochastic resonance algorithm
Yi Xu, Rui Wang
Aiming to the noise effect on weak signal extraction in the laser off-axis scattering detection, the signal processing technique, which applies the stochastic resonance that when the stochastic resonance among input signal, noise and nonlinear system is reached the output signal noise rate (SNR) is improved by converting the power of noise into the signal, is put forward. On the adaptive stochastic resonance theory, the new algorithm combining the genetics algorithm and adaptive resonance algorithm, which is optimized by applying niche technique and 'cross generational elitist selection' strategy. Meanwhile, the concrete realization description and stimulation are made out. It shows that the weak can be well detected from the low SNR circumstance, and the new method by that in the laser off-axis scattering detection the noise effect on weak signal extraction is weakened, is found. The method is promising in the applications such as laser alarm.
Study on the characteristic of energy response of large sampling device to ultra-high energy laser diagnosis
Xinrong Chen, Chaoming Li, Jianhong Wu
In terminal optical system of the ICF (inertial confinement fusion) , the large caliber (310mm*310mm) beam sampling grating (BSG) is used to confirm the energy of the main laser by measuring the -1st transmission diffractive light intensity of the main laser beam.The characteristics of BSG's energy response directly affects the measurement accuracy. The characteristic of BSG's energy response has been studied in this paper based on the actual intensity distribution of the ultra-high energy laser beam and the spatial distribution model of diffractive efficiency of BSG. BSG's energy response affected by its uniformity of the diffractive efficiency has been analysised, too. The results indicate that the spatial distribution of diffractive efficiency of BSG is directly related to the energe response characteristics and the uniformity of BSG's diffractive efficiency has an impact on the accuracy of the sampling of energy.This research provides a theoretical basis for evaluating the high-energy sampling device's energy response characteristic in ultra-high energy diagnosis. The technical indicator with the uniformity of BSG's diffractive efficiency has been attained and these results are use for the fabrication of the beam sampling gratings in practice.
Soft demodulation to the optical pulse position modulated signals
Tian-hua Zhou, Wei-biao Chen
The optical Pulse Position Modulation (PPM) is applied widely in Free Space Optical communication (FSO) with the low average power and the high peak power. The transmitted PPM information depends on the location of the coming optical pulse signals in fixed period. Both receiver and transmitter should been kept in time slot synchronization and frame synchronization in demodulation. Because the channel is very complex, the received optical pulse width will be stretched randomly. We design and realize one digital PPM modulation receiver with high sensitivity using the technology of PMT, A/D converter, and DSP. It is suitable to the total digital optical receiver with random time slots and random pulse width. The paper will mainly discuss the realization of the soft demodulation behind A/D converter. The key of PPM digital soft modulation is the establishment of the synchronization that involves the segment synchronization, the fame synchronization and the bit synchronization. The synchronization can be obtained by seeking for the frame head in data frames. Based on the estimation of received waveform characteristics, we adopt a matched filter without the best factors firstly. Thereafter, their errors will be self-adapted while finding the synchronization head. Considering the real-time need, we choose the reduced mode of maximum likelihood function judgment finally. In the experiments, results with high sensitivity and low bit error rate have been achieved.
Quantitative analysis of multi-elements in steel samples by laser-induced breakdown spectroscopy
Lan-xiang Sun, Hai-bin Yu
Through a Nd:YAG pulse laser of 1064nm wavelength, a multichannel grating spectrometer, and seven CCD detectors, the plasma emission spectrum of the 200 - 980nm wavelength rang were simultaneously observed. First, we studied the influences of some factors like laser energy and measurement time delays on emission intensity of plasma. By experiments, we found that the unusual phenomenon that the emission intensity of plasma is possibly stronger when laser energy is smaller for steel samples. However, this stronger intensity obtained under smaller laser energy is not suitable to quantitative analysis because of poorer repetition. Second, we determined the optimal experimental parameters and quantitatively analyzed the concentrations of the element Mn, Ni, Cr, V, Ti and Cu in some steel samples under the optimal experimental parameters. The calibration curves of these elements were built, and good linearity was obtained. The average relative errors of the quantitative results of these elements are between 13.31% and 4.54%. Consequently, LIBS can be used for quantitative analysis for steel samples; however, the accuracy of the quantitative results still needs to be improved.
UV Raman lidar for fine detection of atmospheric relative humidity profile
Yufeng Wang, Dengxin Hua, Jiandong Mao, et al.
An ultraviolet Raman lidar system at 354.7nm laser wavelength has been developed to measure the elastic scattering signal and the vibrational Raman scattering signal of N2 and H2O for fine-detection of atmospheric humidity profile. A newly spectroscopic filter structured with a high-spectral-resolution grating and two narrow band mirrors are used to separate those backscattering signals finely. The density of humidity is derived from the vibrational Raman scattering signal of N2 and H2O, the relative humidity profile is obtained combining with the temperature profile taken simultaneously by Raman temperature lidar. Some preliminary experiments have been carried out in nighttime at Xi'an area, the wator vapor mixture ratio vertical profile is analyzed. The experiments results indicate that a measurement error of the relative humidity less than 10% is obtained within the atmospheric boundary layer under the condition of laser energy of 300mJ and observation time of 10min.
Comparative analysis of the multi-type atmospheric aerosol lidar ratios
Yong Han, Daren Lü, Minzheng Duan
For lidar probing technique, the lidar ratio is one of key factors which impact the precision of lidar detection. Lidar ratio depends on not only incident laser wavelength but also aerosol size distribution and complex refractive index, and its value is between 0 and 90sr. However, lidar ratio was simply suggested as a fixed value of 50 sr for a long time, which means that the atmospheric aerosol size distribution and chemical compositions do not change with temporal and special variableness. In order to improve the detection precision of lidar extinction profile, it is necessary to study the changes of lidar ratio. For the measurements with an upward-looking monostatic lidar system, due to the change of the relative humidity along the measurement path, the lidar ratio may differ considerably from an assumed constant range-independent value. One of the objectives of this study is to quantify this variability for different aerosol types by numerical methods, and we will give out multi-type aerosol lidar ratios, such as continental clean, continental average, continental polluted, urban, desert, maritime clean maritime polluted and maritime tropic et al. The results will provide valuable references for the lidar development and the derivation of atmospheric aerosol extinction profile.
Exhaust gas monitoring based on absorption spectroscopy in the process industry
Shuai Zhang, Wen-qing Liu, Yu-jun Zhang, et al.
This non-invasive gas monitor for exhaust gas monitoring must has high reliability and requires little maintenance. Monitor for in-situ measurements using tunable diode laser absorption spectroscopy (TDLAS) in the near infrared, can meet these requirements. TDLAS has evolved over the past decade from a laboratory especially to an accepted, robust and reliable technology for trace gas sensing. With the features of tunability and narrow linewidth of the distributed feedback (DFB) diode laser and by precisely tuning the laser output wavelength to a single isolated absorption line of the gas, TDLAS technique can be utilized to measure gas concentration with high sensitivity. Typical applications for monitoring of H2S, NH3, HC1 and HF are described here together by wavelength modulation spectroscopy with second-harmonic(WMS-2F) detection. This paper will illustrate the problems related to on-line applications, in particular, the overfall effects, automatic light intensity correction, temperature correction, which impacted on absorption coefficient and give details of how effect of automatic correction is necessary. The system mainly includes optics and electronics, optical system mainly composed of fiber, fiber coupler and beam expander, the electron part has been placed in safe analysis room not together with the optical part. Laser merely passes through one-meter-long pipes by the fiber coupling technology, so the system itself has anti-explosion. The results of the system are also presented in the end, the system's response time is only 0.5s, and can be achieved below 1×10−5 the detection limit at the volume fraction, it can entirely replace the traditional methods of detection exhaust gas in the process industry.
Investigation on offset frequency locking system for a short-pulse laser
Rui Yao, Qi Li, Kai Xue, et al.
Offset frequency locking is widely applied in laser detection, frequency stabilization of lasers, laser accurate measurement and laser spectroscopy. In the paper, an offset frequency locking system based on Field Programmable Gate Array (FPGA) is designed and applied for cavity-dumped CO2 waveguide laser with two channels and common electrodes. A scheme for all-digital frequency discriminator in the system is described in the paper. The frequency discriminating precision of single pulse is improved by designing a high speed counter which could count both the rising edges and falling edges of signals. The multi-pulse discrimination and the high probability mean filtering algorithm are used to further improve the discriminating precision. At the same time, the algorithm of variable step length and segmental approximation is used to improve the speed and precision of frequency modulation. The experimental results show that with the method of multi-pulse discrimination the beat frequency is stabilized within ±10MHz.
The research of improving the efficiency of space coherent optical detection
Hong-yan Jiang, Ning He
Coherent optical detection technique has been widely used in communication and non-communication fields due to its advantages in handling kinds of modulation formats and offering improved sensitivity and signal to noise ratio. We present an acousto-optic signal processing system using coherent detection technique. Firstly the principles of Bragg diffraction and coherent optical detection are introduced. And then how to combine coherent detection with acousto-optic deflection to achieve signal processing is discussed. As to improve the efficiency of the space coherent optical detection, an approach that signal and reference beams are respectively injected into corresponding polarization-maintaining (PM) fibers before combining is put forward. In this way, the fluctuation of the state of polarization of the two beams is overcome. Through beam collimation, polarization-state control and Fourier transform (compression processing), the acousto-optic deflector is ensured to get higher diffraction efficiency over the whole frequency band of operation. Meanwhile, the impact that the surrounding environment has on the mixing of signal and reference beams is decreased, and the level of complexity and difficulty in optical system alignment is also reduced. At last, computer simulation has shown that the SNR is much depended on the linewidth of laser. When the coupling optical aperture and laser energy injection efficiency are ensured to meet demands, experiments have proven that, by injecting beam into PM fiber, the influence background light has on combining is weakened so that it is easier to keep polarization matched between signal and reference beams, and thereby the efficiency of coherent optical detection can be greatly improved.
Target detection method based on the single laser return waveform
Nanxiang Zhao, Yihua Hu, Min He
The improving resolving power of laser imaging system is limited by the laser footprint size on the target. Employing only echo delay and intensity information, the information of the targets inside the footprint is difficult to be obtained for the echo signal of the targets maybe is submerged by each other. Under the remote laser imaging, the serious loss of image quality may occur because of the large footprint. The target detection method based on the single laser return waveform was studied and the provided to get the target information inside the laser footprint. Firstly, the basis laser echo signal model of the target inside the footprint was built. On the basis, the decomposition algorithm was provided which can decompose a laser return waveform into a series of components assuming that each component corresponding to a sub-target inside the laser footprint. After the primary sub-target return waveforms was obtained, however, there still exists some small sub-targets inside the laser footprint whose return signal is hardly to be extracted because they are submerged by the neighborhood sub-target return signal. The subtracting algorithm between the whole return waveform and the components waveform provides the way to get the submerged return waveforms of sub-target. So, the information of sub-targets inside the laser footprint would be obtained. In the end, the actual laser return data was analyzed employing the method to get the range position information of the sub-targets inside the laser footprint, which verifies the method validity.
Simulation of the solid state laser relay mirror system
Hui-yun Wu, Jin-bao Chen, Wu-ming Wu, et al.
The laser relay mirror technique has been under extensive research in recent years. The concept and the working process of the relay mirror system are analyzed in this paper. The model of the relay mirror system is established, the effect on 1km-altitude target with 500 m/s flying speed of the relay mirror system and the conventional ground-based laser system are calculated respectively. Obtains that the maximum coverage range of the ground-based laser system is 2.0 km and the maximum coverage range of the relay mirror system is 23.2 km. The relay mirror can largely open up the coverage range of the laser system and strengthen the attacking ability of the ground-based laser.
Fabrication of the nanostructure metal film
Zhiqiang Mi, Xiaoxuan Xu, Junmei Li, et al.
With the use of nano-structure metal film and the angle incident laser which has specific wavelength and polarization, it will form surface plasma resonance, and we can see several orders of SERS phenomenon. This phenomenon can be widely used in the area of military. Such as the detection of the mine, the investigation of the concentration of toxic gas. This paper mainly describes a way of fabrication of the nano-structure metal film: at first fabricate a honeycomb structures of aluminum oxide template, the second plate the alumina template with silver, at last dissolve the alumina template with hydrochloric acid. Thus ordered silver nano arrays is formed. Experiment prove it is a very well substrate for SERS.
A hybrid method for synthetic aperture ladar phase-error compensation
Zhili Hua, Hongping Li, Yongjian Gu
As a high resolution imaging sensor, synthetic aperture ladar data contain phase-error whose source include uncompensated platform motion and atmospheric turbulence distortion errors. Two previously devised methods, rank one phase-error estimation algorithm and iterative blind deconvolution are reexamined, of which a hybrid method that can recover both the images and PSF's without any a priori information on the PSF is built to speed up the convergence rate by the consideration in the choice of initialization. To be integrated into spotlight mode SAL imaging model respectively, three methods all can effectively reduce the phase-error distortion. For each approach, signal to noise ratio, root mean square error and CPU time are computed, from which we can see the convergence rate of the hybrid method can be improved because a more efficient initialization set of blind deconvolution. Moreover, by making a further discussion of the hybrid method, the weight distribution of ROPE and IBD is found to be an important factor that affects the final result of the whole compensation process.
Performance analysis of range-gated active imaging system
Hua-yan Sun, Hui-chao Guo, Ying-chun Li
The performance of passive photoelectric detection system for target detection is seriously affected by many factors, such as the background light, the weather condition and the target temperature contrast, etc. To overcome the disadvantages of the passive detection system, lots of domestic and foreign institutes are focusing on the research of the laser active imaging detection system. Laser active imaging system based on range-gated technology use high peak power laser pulse to illuminate the target, meanwhile use the receiving system with synchronization control circuit to detect part of the reflected light from the target for imaging. It can efficiently suppress the brightness noise and the backscattering noise, and apparently advance the imaging and identification performance for small dark target far away. In this paper, on analyzing the principle of the range-gated laser active imaging technology, we studied the system range performance limited by SNR thresholds due to the detector noise and the background noise respectively. By analyzing in theory and simulation calculation, we made out the relationship between system range performance and other system parameters in certain atmosphere conditions. The parameters include peak laser power, laser divergence angle, imaging system resolution, target contrast, system SNR, etc.
All-fiber double-balanced laser coherent detection system
Zhao-hua Meng, Guang-lie Hong, Rong Shu, et al.
Laser coherent detection makes use of the coherence of laser to pick up weak laser signal by an optical LO (local oscillator) signal. Compared to direct detection, coherent detection has higher sensitivity and could get the frequency difference between incident signal and LO. Traditional coherent detection systems are composed of free space optical components; the systems were complicated and hard to adjust. We built an all-fiber MOPA heterodyne laser detection system by DFB laser, AO frequency Shifter, polarization beam splitters, polarization maintaining couplers and balanced photo receivers. Because the coherence of laser beams is relative to the alignment of polarizations states, our system uses double-balanced structure. The balanced detection structure greatly reduces the relative intensity noise of the LO. In the article, the theory of coherent detection and the double balanced coherent detection are presented; the design of detection electronic circuits is also discussed. The high coherent efficiency of fiber-optic detection system and high sensitivity of coherent detection are proved by experiment. Some problems caused by fiber optics are also introduced.
Influence of turbulent atmosphere on laser beams from confocal unstable resonators
Yu-feng Peng, Juan Wang, Xiao-qun Bi, et al.
Based on the laser fields from a positive confocal unstable resonator (ab initio), the propagation characteristics of the beam through turbulent atmosphere are investigated by means of fast Fourier transform algorithm (FFT). To conveniently investigate the propagation characteristics of laser beam through the atmosphere, as far as known, in the previous many works, a mathematical expression was generally artificially predefined to represent the given laser beam, such as Gaussian beam, Hermite-cosh-Gaussian beam, flat topped beam, dark-hollow (annular) beam, etc. In this paper, by basing on the initial built in oscillation of a laser resonator, such as a positive confocal unstable resonator (CUR), we studied the intensity distributions of the output laser field to obtain the propagation characteristics of laser beam through the turbulent atmosphere as functions of different propagation distances. The results show that the turbulence will result in the degradation of the peak value of the laser intensity in the far field, the spread of the far field diagram patterns, and the beam quality characteristics greatly degraded.
Laser speckle reduction using a dynamic polymer-based diffraction grating spatial phase modulator
M. N. Akram, V. Kartashov, K. Wang, et al.
Speckle is the constructive and destructive interference pattern observed from an optically rough surface when a highly coherent laser light is used as the illumination source. In this article, we present some methods to reduce the undesired laser speckle in laser display projector and show measurement results indicating reduction in speckle contrast obtained by using a dynamical flexible polymer-based diffraction grating phase modulator. Light is diffracted into multiple orders by the dynamic polymer diffraction grating. This diffracted light, after collection and homogenization, is used as the illumination source for displaying picture information. Due to the time-varying phase of the diffraction grating, the diffraction pattern changes thus creating time-varying speckle patterns on the rough screen. The time-varying speckle is captured by a CCD camera with appropriate integration time to mimic the averaging action of the human eye. Thus the time-integrated speckle is minimized by the intensity averaging of many independent speckle patterns. Different configurations of the diffraction grating along with random phase plate and beam combining lens were explored to ascertain the corresponding reduction in speckle contrast and its dependence on the time-period of the driving voltage of the diffraction grating.
Simulation experiment of high energy laser propagation in the atmosphere
Chun-Hong Qiao, Xiao-Xing Feng
Simulation experiment of adaptive optics compensation to thermal blooming phase distortion induced by high energy laser propagation in the atmosphere are carried out. The results of spot pattern and Strehl ratio in the focal plane are obtained when the adaptive optics system is in the open or closed loop shape. The effect of adaptive optics compensation is prominent when the Bradley-Hermann distortion number ND is less than 300, and Strehl ratio is more than 0.4 on the whole. Phase compensation instability appears when the distortion number ND becomes greater than 300, in this case, the compensated beam Strehl ratio goes down rapidly. The experimental Strehl ratio without adaptive optics compensation agrees well with that of the thin lens approximation theory, while the one with adaptive optics compensation has some deviation with that of the ray-optics approximation theory.
Accuracy improvements of gyro-based measurement-while-drilling surveying instruments by a laser testing method
Rong Li, Fan Li
Gyroscope used as surveying sensor in the oil industry has been proposed as a good technique for measurement-whiledrilling (MWD) to provide real-time monitoring of the position and the orientation of the bottom hole assembly (BHA).However, drifts in the measurements provided by gyroscope might be prohibitive for the long-term utilization of the sensor. Some usual methods such as zero velocity update procedure (ZUPT) introduced to limit these drifts seem to be time-consuming and with limited effect. This study explored an in-drilling dynamic -alignment (IDA) method for MWD which utilizes gyroscope. During a directional drilling process, there are some minutes in the rotary drilling mode when the drill bit combined with drill pipe are rotated about the spin axis in a certain speed. This speed can be measured and used to determine and limit some drifts of the gyroscope which pay great effort to the deterioration in the long-term performance. A novel laser assembly is designed on the wellhead to count the rotating cycles of the drill pipe. With this provided angular velocity of the drill pipe, drifts of gyroscope measurements are translated into another form that can be easy tested and compensated. That allows better and faster alignment and limited drifts during the navigation process both of which can reduce long-term navigation errors, thus improving the overall accuracy in INS-based MWD system. This article concretely explores the novel device on the wellhead designed to test the rotation of the drill pipe. It is based on laser testing which is simple and not expensive by adding a laser emitter to the existing drilling equipment. Theoretical simulations and analytical approximations exploring the IDA idea have shown improvement in the accuracy of overall navigation and reduction in the time required to achieve convergence. Gyroscope accuracy along the axis is mainly improved. It is suggested to use the IDA idea in the rotary mode for alignment. Several other practical aspects of implementing this approach are evaluated and compared.
Design of Er:YAG laser blood-sampling device
Zhi-chao Wu, Guang-yong Jin, Xue-chun Tan, et al.
Laser blood-sampling device is one of the foremost tasks in medicine domain. It has a lot of merits such as un-touching, avoiding infection, indolence, and fast healing etc. The Er:YAG laser with wavelength of 2.94μm which is just close to the absorbency peak of water can be strongly absorbed by water molecular, so it has very wide application value in clinical medicine. In the paper, based on the mutual action characters of the laser with 2.94μm wave length on biological tissues, such as high absorption, acting on surface, the design of a new type of laser blood-sampling device is introduced. According to the needs of practice, the main component of the blood-sampling device is the laser, which includes optical resonator, optical collector, pumping source, optical guidance and focusing system. All of them are designed in the paper, and the reflection index of output coupling mirror of laser is optimized, the laser threshold is reduced, and pumping efficiency is improved. Moreover, thermal effect of Er:YAG solid-state laser is analyzed and a reasonable cooling method is designed. As a result, an excellent laser blood- sampling is obtained, the maximum output power is about 1J, the optical to optical conversion efficiency is 1.2%. For the better production-grade, the cuprum-based conduction is adopt to eliminate heat, the precision modulation and fixing of the optical resonance is achieved by the special adjusting structure that not only improve the stability and reliability, but also reduce the size of laser bloodsampling device. The size is 110×190×320mm, the weight is about 5.8kg, and the laser blood- sampling efficiency is 100%.
Extracting turbulence information from echo signal of micro-pulse lidar
Zhi-bo Ni, Hong-hua Huang, Hai-ping Mei, et al.
Based on the method of measuring turbulence profile with lidar, equations of backscattering speckle sizes induced by aerosol and turbulence are given. According to the relationship between diaphragm aperture and sizes of speckles, fluctuations of normalized variance of echo signal can be separated into dilution regime of aerosol and turbulence, turbulent regime and smoothed regime. The feasibility of measuring turbulent profile with MPL-A1 lidar is discussed, and experiments are performed in horizontal direction. According to the values of SNR and values of normalized variance of echo signal, effective measuring distances of this lidar are determined. The variations of normalized variance and those of calculated results of scintillation index, which are both depending on propagation distance, are compared. Results show that, although the values of normalized variance are only 10 percent of the latter, there is much comparability, especially during nighttime. Temporal variations of normalized variance, which are calculated at 1950m during daytime and at 4500m during nighttime, are compared with those of refractive index structural constant. Analyses show that, the fluctuant ranges of them are all about one magnitude. Although there are a small quantity of time differences between them, total tendencies are comparable.
Laser underwater image target detection based on Gabor filter
Shu-bin Yang, Yun-han Wang, Yi Tian
Laser underwater target image acquired by using synchronization-scanning imaging technology is always disturbed by strong laser beam. Correlation analysis algorithm based on texture-driven cannot detect target in these images at first hand. In these laser images energy of mighty laser beam is converged in a certain direction, on the contrary distribution of weak target energy is symmetrical in all directions. Some certain multi-scale and multi-channel Gabor filters can boost up some certain direction energy and at the same time decrease other certain direction energy. Therefore, the mighty laser beam with single certain direction in the image is restrained by appropriate Gabor filters. In order to gain the better result, firstly small size Gabor filters with four directions are used to process the laser target image, then scale size of Gabor filter is increased step by step until result image processed by Gabor filters is approving. After that texture-driven correlation analysis algorithm is processed on the image filtered by Gabor filters with appropriate size and direction and then weak target is detected. Experiments prove that the proposed algorithm based on Gabor filter can efficiently eliminate interference of mighty laser beam and detect laser underwater image target effectively.
Accuracy analysis of optical ranging in atmosphere
Hong-wu Yuan, Yin-bo Huang, Hai-ping Mei, et al.
Optical ranging is one of the most precise techniques for distance measurement. The effects of the density variation of atmosphere, aerosols and clouds on optical ranging precision are generally considered, a new method is proposed for calculating the ranging precision in the presence of aerosol particles and clouds. The size distribution spectrum models for aerosols and clouds in the Optical Properties of Aerosols and Clouds Package (OPAC) are adopted. Results show that aerosols and clouds could introduce errors of several centimeters to several ten meters to the ranging. The relationship between the ranging precision and the relative humidity, the zenith angle of ranging direction and the optical wavelength is also analyzed. The ranging error doesn't have an obvious relationship with the wavelength, but depends on the zenith angle, especially for the angle larger than 70 degree. The ranging error depends on the relative humidity as well. The ranging error induced by aerosols increases gradually with the increase of the relative humidity when the relative humidity is less than 80%, but it increases rapidly when the relative humidity is larger than 80%. Our results could provide a theoretical basis and reference for the application of optical ranging.
Imaging lidar for occluded target recognition
Yuan-nan Xu, Yuan Zhao, Yong Zhang, et al.
The detection and recognition performance of photoelectric detector for occluded target is very important in complicated battlefield environment. It is one of the key factors to win a battle. Three key techniques of imaging lidar for occluded target recognition are investigated, including the range-gated scannerless imaging, determination of range gate, spectrum and polarization imaging. The range gate is determined by using modulated gain, pulse width measurement and inference distinguishing of ground object echo and movement flatform. The project of an imaging lidar for occluded target recognition is designed through the combination of hardware and software algorithm.
The research of the thermal effect and experimental test of the beam phase properties for the Q-switched LD pumped laser
Xiang Zhang, Jing Luo
The results of an experimental and theoretical study of the proprerties of a LD pumped laser using a plano-concave stable resonator are presented. The influence of thermal lens effect on laser output mode and beam quality has been discussed briefly by using the transfer matrix theory. In this paper, further experiment on the output beam quality of a LD pumped acousto-optic Q-switched laser has been also performed by adopting Hartmann-Shack wavefront sensor and Zernike mode reconstruction theory. Using this method, the PV and RMS values of the aberration wavefront, the frontal 35-order Zernike aberrations can be acquired, and the Strehl ratio curve of the output beam and the distribution of circle energy can also be obtained by calculation, so the mode properities can be fully understood. The experimental results show that the beam wavefront aberration is mainly concentrated in the frontal 15 orders of Zernike aberration, mainly including the defocus A3, the low-order astigmatism A4 and A5, and the coma aberration A6 and A7 because of the crystal thermal effect.
A common evaluation standard for an airborne LiDAR system
Keshu Zhang, Qiang Gong, Bin Xu
Faced with different parameters in nowadays commercial airborne LiDAR market, a common evaluation standard based on the user requirements including data quality and efficiency was developed to help users select a proper device. In this paper, user requirements and data evaluating method were firstly discussed to build up a link between accuracy and acquired footprints. Then, the relations between the coordinates of footprints and parameters were thoroughly analyzed. The parameters were classified into basic and derived parameters, and a common evaluation standard was set up to uniform these parameters according to data quality and efficiency. Furthermore, to demonstrate the effectiveness of the standard, different parameter configurations were presented according to three different scenarios. The common evaluation standard will help users to clarify and uniform the understanding of parameters.
Laser-induced photoacoustic glucose spectrum denoising using an improved wavelet threshold translation-invariant algorithm
Zhong Ren, Guodong Liu, Zhen Huang, et al.
In this paper, the photoacoustic spectroscopy (PAS), a novel, hybrid, noninvasive imaging modality, is used to monitor the change of glucose concentration. A laser light with wavelength of 532nm is irradiated into the sample, The PA signal is detected by the ultrasonic transducer based on the thermal-expansion effect, which can reflect the biochemical properties of the biological tissues e.g., blood. Although PAS has better resolution and deeper penetration than others, the PA signal is unavoidably polluted by some noises. In order to remove these noises to improve the precision and the signal-to-noise ratio(SNR) of the glucose concentration, an improved wavelet threshold function is proposed. Meanwhile, to eliminate the Pseudo-Gibbs phenomenon, the improved threshold function combines translation-invariant(TI) algorithm to further improve the denoising effect. This threshold function can be looked as the compromise between Donoho's soft-threshold function and hard-threshold function. Experimental results show that the denoising result of improved function is better than that of Donoho's threshold functions and the semisoft-threshold function proposed by Gao, etc. The improved function with combined TI algorithm denoise not only gets higher SNR and lower root-mean-square error(RMSE), but makes the PA glucose spectral smoother. The SNR increases from 27.3658 to 44.7060, the RMSE decreases from 0.272 to 0.017.
Modelling of an active burst illumination imaging system
Nicolas Rivière, Laurent Hespel, Marie-Thérèse Velluet, et al.
Onera, The French Aerospace Lab, has developed a new active burst illumination imaging system with a short time gating. This imaging device is used to obtain a passive or an active image of a small volume of the illuminated scene. To better understand and evaluate the relevant physical phenomena (scintillation, speckle...) impacting on the performance on burst illumination imaging system, Onera has implemented a code (PIAF). The aim of this paper is to describe the model and to present some first results. Efforts have done on three principal points, the laser source model, the propagation through the turbulence concerning the illumination of the scene, and the interaction with the target. The model can take into account any laser sources. To evaluate the propagation through the atmosphere, electromagnetic models are implemented but we specially focused our attention on simplified methods to reduce computing time. Considering the 3D target and its elementary plane surfaces, we analyze each contribution like the incoherent solar field or the incident laser field. We adapt classical and physical models for light reflection. Speckle contributions are also treated using data bases generated by an Onera tool. In the last section of this paper, we attempt to model artefacts associated with such imaging devices, including photon noise, gain issues and electronic noise. We also present experimental results and comparisons with Piaf simulations in an associated paper.
Comparison of a physics-based BIL simulator with experiments
L. Hespel, M. T. Velluet, A. Bonnefois, et al.
Laser Gated Imaging is a unique camera technology. It provides long-range night vision in complete darkness as well as in degraded weather conditions, such as rain, fog and haze. Burst illumination laser (BIL) imaging combines an active laser illumination with time gating (or range gating) camera. For these reasons, BIL imaging has become increasingly important in Defense and security applications. In an associated paper [01], we present a model (PIAF) developed to evaluate the relevant physical phenomena (scintillation, speckle...) impacting on the BIL imaging. This paper presents preliminary experimental results and comparisons with PIAF simulations.
Research on the characteristics of light scattering by underwater air bubble film based on the Monte Carlo method
Yang Yu, Jiang-an Wang, Zhi-guo Ma, et al.
The primary characteristics of light scattering by water medium and small particles are analyzed based on the scattering theory. Compare the differences between two method to fix the deflection angle, one is Rayleigh expressions, the other is sampling the H-G function. The light scattering intensity distribution on conditions of variety of wavelengths and particle's semidiameters are calculated using Mie scattering expressions. The emluator of photon moving underwater is completed, which is validated taking exponential attenuation law of beam transmitting as standard, then several set of simulations proceed, accordingly some rules of underwater optical echo signal are concluded. In the end, the attenuation experiment of beams in different wavelengths, and the experiment of pulse laser detecting underwater air bubble film are conducted.
A promoted ladar imaging system based on gain modulation
Yong Zhang, Yuan Zhao, Liping Liu, et al.
Gain modulation ladar is a cutting-edge ladar system. To eliminate the image distortion caused by target movement, two ICCDs are adopted to detect simultaneously and get the range image of object. This article presents a research on the working mechanism and range resolution of non-scan ladar based on gain modulation. The research suggests that ICCD's relatively low SNR is one of the bottlenecks of further improvement of system performance. To address this issue, an improved system was designed and studied with regard to its range resolution. Experimental results indicated that the proposed system was superior to the ladar system adopting double ICCDs in the aspects of range resolution, etc.
Analysis of laser jamming to satellite-based detector
Si-wen Wang, Li-hong Guo
The reconnaissance satellite, communication satellite and navigation satellite used in the military applications have played more and more important role in the advanced technique wars and already become the significant support and aid system for military actions. With the development of all kinds of satellites, anti-satellite laser weapons emerge as the times require. The experiments and analyses of laser disturbing CCD (charge coupled detector) in near ground have been studied by many research groups, but their results are not suitable to the case that using laser disturbs the satellite-based detector. Because the distance between the satellite-based detector and the ground is very large, it is difficult to damage it directly. However the optical receive system of satellite detector has large optical gain, so laser disturbing satellite detector is possible. In order to determine its feasibility, the theoretical analyses and experimental study are carried out in the paper. Firstly, the influence factors of laser disturbing satellite detector are analyzed in detail, which including laser power density on the surface of the detector after long distance transmission, and laser power density threshold for disturbing etc. These factors are not only induced by the satellite orbit, but dependence on the following parameters: laser average power in the ground, laser beam quality, tracing and aiming precision and atmospheric transmission. A calculation model is developed by considering all factors which then the power density entering into the detector can be calculated. Secondly, the laser disturbing experiment is performed by using LD (laser diode) with the wavelength 808 nm disturbing CCD 5 kilometer away, which the disturbing threshold value is obtained as 3.55×10-4mW/cm2 that coincides with other researcher's results. Finally, using the theoretical model, the energy density of laser on the photosensitive surface of MSTI-3 satellite detector is estimated as about 100mW/cm2, which is largely exceed the disturbing threshold and therefore verify the feasibility of using this kind of laser disturbing the satellite-based detector. According to the results. using the similar laser power density absolutely saturate the requirements to laser disturbing satellite-based detector. If considering the peak power of pulsed laser, even decrease laser average power, it is also possible to damage the detector. This result will provide the reliable evidences to evaluate the effect of laser disturbing satellite-based detector.
Processing methods in frequency domain for bubble laser scattering signals
Liping Su, Weijiang Zhao, Deming Ren, et al.
For the detection of the bubble-laser-scattering property, it is the key to improve the signal to noise ratio. The various noises in the bubble-laser-scattering signal, the background light, power frequency of 50Hz, radio frequency noise and inherent noise within the electronic system, are analyzed in detailed. Two frequency-domain methods used to process the bubble scattering signal, the Fourier transform and the power spectral estimation, are focused on. These two methods can reduce the noise, isolate the DC component and eliminate the impact of the power frequency of 50Hz, thus the pulse of bubble laser scattering could be detected. The physical meaning for the power spectral estimation is much clearer than that of the Fourier transform. The power spectrum curve obtained by using the Yule-Walker AR (regression model) method is much smoother and its frequency resolution is higher than the other methods. The results show that the Yule- Walker AR spectrum estimation is the most reasonable and most effective method.
Eyesafe laser based on a ring-cavity KTP optical parametric oscillator
Xu Liu, Changyong Lu, Yong Cheng, et al.
A high efficient ring-cavity optical parametric oscillator at 1.57μm eye-safe range using three non-critically phasematched KTP crystals is researched and experimentally demonstrated. The primary advantage of the ring-cavity OPO is that the resonator mirrors are at 30 degrees to the pump beam, so they do not provide any feedback to the pump laser. The signal energy of 75mJ with the pulse width of 6.6ns is obtained under the input pump pulse of 200mJ. This result provided a clear demonstration that high pump-to-signal energy conversion (up to 37.5%) can be achieved from the ringcavity OPO by single-pass pumped method.
A novel distributed feedback fiber laser accelerometer
Rui Wang, Yong-jie Wang, Fang Li, et al.
A novel distributed feedback fiber laser accelerometer based on silicon rubber is developed. The unique mechanism employed for the accelerometer ensures uniform strain distribution on the fiber laser's Bragg element. A mathematical model of single-degree-of-freedom system is established, giving the expression of the sensitivity and resonant frequency of the accelerometer. A multiple-degree-of-freedom simulation with finite element method is also conducted, giving a more precise prediction of accelerometer's characteristic. Several accelerometers of this type are constructed and tested. The wavelength shift signal is demodulated using phase generated carrier technique. The experimental result shows they have a sensitivity of 72 pm/G and a resonant frequency of 415Hz, which agree well with the simulation results. The minimum detectable signal of the whole sensing system is about 1.5μg. The accelerometer's structure is simple and the components employed are all commercially available, indicating a great potential in practical use.
Research on design and simulation of a FM/cw lidar system
Jiguang Zhao, Zhiquan Zhang, Chen Deng
The FM/cw lidar has the advantages of narrow receive bandwidth, non-range-ambiguity, enhanced ability of anti-jamming etc. A summary of FM ranging theory is introduced. The FM/cw lidar system is designed with the incoherent detection approach, which contained the transmitter, receiver and signal processing system, the system complexity and realization difficulty are reduced significantly. The transmitter is consisted of chirp signal generate module, laser modulate system and laser transmit subsystem. Receiver is consisted of receive optical system, photo electricity detector, amplifier and mixing. Signal process system is consisted of lowpass, IF amplifier, signal collecting and processing system. The main affect factors are analyzed, the modulate depth and mixing efficiency effect to the detection capability are simulated, which are the special to the FM/cw lidar based on the designed FM/cw lidar system. The simulation results indicate that the detection capability can be improved efficiently by enhance the modulate depth and mixing efficiency. The research results establish the theory and realization basic to the research on the FM/cw lidar.
1000W compound coupling high beam quality diode laser
Youqiang Liu, Yinhua Cao, Chunxiao Xu, et al.
KW-class high-beam quality diode laser system was introduced in this paper. In this system, the wavelengths of 808nm, 915nm, 940nm, and 980nm were used for the wavelength coupling and polarization coupling. The wavelength coupling and polarization coupling can reach the optical efficiency of 91.4%. Before wavelength coupling, polarization coupling and beam shaping, the maximum output power of the laser was 1200W, and after that, 1031W was achieved, so the overall conversion efficiency reached 85.9 %. 12mm • mrad of the output beam quality was realized in both the fast axis and the slow axis. Through intelligent control, the diode laser can work in different wavelength, different power and different pulse width. Because of its output power and beam quality, this laser system can be used in the ultra-long-distance laser detection, laser remote sensing and many other demands.
Long-term laser frequency stabilization for application in sodium resonance fluorescence Doppler lidar
Zhaoai Yan, Xiong Hu, Shangyong Guo, et al.
This paper mainly reports long term laser frequency stabilization combined Pound-Drever-Hall technique with Dopplerfree saturated spectroscopy technique for application in sodium resonance fluorescence Doppler lidar. A single-mode dye laser with Pound-Drever-Hall frequency stabilization is employed in this lidar system. But the center frequency of the laser can drift due to temperature changes or piezo actuator relaxation. To reduce these drifts, a sodium Doppler-free saturated fluorescence spectroscopy system is set up and the sodium Doppler-free features are used as absolute frequency references to lock the laser frequency. A sodium vapor cell is heated to and stabilized at 65ºC in order to provide sufficient atomic sodium vapor density. A photodiode is placed adjacent to the sodium vapor cell to detect the laserinduced fluorescence. The frequency stabilization operation is based on LabVIEW program.In reaction to the error signal, this software program will act via the dye laser controller on the reference cell piezo actuator to keep the master resonator on the sodium fluorescence spectrum line. In this lidar system, we lock the laser frequency at sodium D2a line with ~4MHz precision for hours.
Parametric edge detection for ladar intensity image with different carrier-noise-ratio
Ming Zhou, Qi Li, Qi Wang
Parametric edge detector has been reported to be successfully applied in actual coherent ladar intensity images corrupted by speckle. Parametric edge detector derived from an exponential model for the speckle which has been described as a multiplicative noise corrupting intensity images. The performance of the noises is not the same when the intensity images are gained in different distance. So the application scope of this algorithm is of great value in actual ladar. In the paper, parametric edge detector, morphological filter based on parametric edge detector and Canny detector are used to detect coherent ladar simulated intensity images. The edge detection results are obtained and compared, when the values of carrier-noise-ratio (CNR) are changed. From the simulation results, the best application scope of parametric edge detection is described.
Numerical simulation of heterodyne efficiency of coherent imaging ladar using rectangular element detector
Huaiyong Zhang, Qi Li, Qi Wang
In coherent imaging ladar system, the round-trip time and the scan rate cause the deviation between the received signal and the transmitter beam in spatial directionality. Therefore the return signal angle lags behind the receiving optical axis angle. This lag-angle effect will cause energy loss and even the loss of return signals, which would finally affects the image quality. In order to overcome the impact of lag-angle effect on image quality, the detector with rectangular active area has been presented to replace the circular detector. In this paper, the numerical simulation of heterodyne efficiency based on rectangular detector is analyzed. And the simulation results show that heterodyne efficiency quickly declines with offset of return signal along optical axis when lag-angle effect exists. When the offset is below 0.5 and the length-width-ratio is around 1.5, the heterodyne efficiency is above 50%.
Comparison of various emissions from the laser dye solution under picosecond laser pulse pumping
Shuzhen Fan, Xingyu Zhang, Qingpu Wang, et al.
We experimentally measured the spectral and the temporal properties of various emissions from the Rhdamine 6G dye solution pumped by picosecond laser pulses. These emissions involve the transverse amplified spontaneous emission (ASE), the longitudinal ASE, the longitudinal ASE coupled with partial and stronger coherent feedback, and the random laser. The random laser is made by adding TiO2 nanopowder to the dye solution as scatterer. The spectral and the temporal shapes and widths of these emissions are measured using a spectrometer and a streak camera combined with a CCD. The transverse ASE and the longitudinal ASE have similar spectral widths, while the longitudinal ASEs coupled with the coherent feedback show narrowed spectral widths. The pulse shapes and widths of the longitudinal ASE with coherent feedback show how the coherent feedback comes to existence. The experimental results show clearly the effect of the degree of the coherent feedback on the spectral narrowing. The spectra and the pulses of the random laser of some scatterer densities are presented, showing that the random laser without sharp peaks also has partial coherent feedback in it at certain scatterer densities in the weak scattering regime.
Detection of reactive oxygen species in mainstream cigarette smoke by a fluorescent probe
Li Liu, Shi-jie Xu, Song-zhan Li
A mass of reactive oxygen species(ROS) are produced in the process of smoking. Superfluous ROS can induce the oxidative stress in organism, which will cause irreversible damage to cells. Fluorescent probe is taken as a marker of oxidative stress in biology and has been applied to ROS detection in the field of biology and chemistry for high sensitivity, high simplicity of data collection and high resolution. As one type of fluorescent probe, dihydrorhodamine 6G (dR6G) will be oxidized to the fluorescent rhodamine 6G, which could be used to detect ROS in mainstream cigarette smoke. We investigated the action mechanism of ROS on dR6G, built up the standard curve of R6G fluorescence intensity with its content, achieved the variation pattern of R6G fluorescence intensity with ROS content in mainstream cigarette smoke and detected the contents of ROS from the 4 types of cigarettes purchased in market. The result shows that the amount of ROS has close relationship with the types of tobacco and cigarette production technology. Compared with other detecting methods such as electronic spin resonance(ESR), chromatography and mass spectrometry, this detection method by the fluorescent probe has higher efficiency and sensitivity and will have wide applications in the ROS detection field.
A comprehensive underwater laser imaging model based on temporal and spatial broadening
You-wei Huang, Wei-qi Jin, Kun Ding, et al.
The imaging of underwater objects which have been illuminated by natural or artificial light has been of long-standing interest to investigators working in oceanographic environments. Analysis of the propagation of imaging light through water is complicated by extreme attenuating and scattering properties of water, especially multiple scattering. A comprehensive computer model to simulate the formation of underwater images has been presented in this article. The model incorporates the temporal and spatial broadening properties of the propagation of light in water. A degraded image is approximated as a convolution of an initial image and point spread functions (PSFs). The spatial PSF plays a significant role in describing the spatial propagation of light and image blurring due to forward scattering. The temporal PSF can describe the pulse broadening effect, which is of great significance to evaluate the performance of range-gated technology. Computed and measured images compare favorably. It is concluded that the use of spatial and temporal broadening models are convenient and viable techniques for analytic computation of underwater images.
Dynamic analysis and optimal design of exposure device of laser detector based on a virtual prototype
Da Xu, Jian-xun Zhao, Jun-biao Hu, et al.
The dynamical simulation model of the exposure device of laser detector is built up in ADAMS software. Aiming at optimizing the movement law of the pole and minimizing the maximal value of load of key parts, the influences of the spring stiffness coefficient,the damping coefficient, preload of spring and the mass of pole on the optimal goal are discussed. The virtual prototype of the exposure device of laser detector has been optimized and the optimized parameters are obtained. In order to choose the electromotor and material, intensity of key parts is checked based on ANSYS. And the problem of TQC is solved effectively by this way.
Orientation determination of single molecules by highly focused generalized cylindrical vector beams
Xianghui Wang, Shengjiang Chang, Lie Lin, et al.
The orientation of the dipole moment, which is one of important parameters in single-molecule fluorescence spectroscopy, is determined by highly focused generalized cylindrical vector beams combined with a confocal far-field microscope. A generalized cylindrical vector beam can be decomposed into a linear superposition of radially polarized and azimuthally polarized components and the ratio of the radial and longitudinal components of the focal electric field can be adjusted by changing the polarization direction. As compared to the case of a radially polarized incident beam, numerical results demonstrate that fluorescence intensity difference among single molecules with different orientations can be effectively overcome for a particular polarization direction of the generalized cylindrical vector beam, which may increases the signal-to-noise ratio of the practical experiments and then ease the difficulty in orientation determination of single molecules.
Geometric equivalent solutions of AGRIN surface to aspheric surface
Cunhua Zhao, Zhouqin Wang, Zhaojun Liu
Among novel optical design methods axial gradient index (AGRIN) gradually evokes attention accompanying by manufacture technical maturity. In many papers AGRIN lens is equivalent to an aspheric plano-convex doublet whose curvatures and radii are AGRIN vertexes's and plane surfaces are face to face. Nevertheless the aberrations after the treatment are very drastically changing. To finding accurate equivalent relations is necessary. In our work geometric ray track and numerical calculation are done and the accurate relations of AGRIN surface to aspheric surface are achieved. At last an AGRIN singlet for rotating image is demonstrated to verify the validity of our results. A simulation is carried out through optical design software and little aberrated variety is found. After merit treatment obtained aspheric coefficients approach calculated values.
Propagation properties of partially coherent dark hollow beams with rectangular symmetry through aligned paraxial optical systems
Jia Li, Yan-ru Chen, Qi Zhao, et al.
Propagation properties of partially coherent dark hollow beams with rectangular symmetry through aligned paraxial optical systems are investigated in this paper. Based on the unified theory of coherence and polarization, the analytical formulae for cross-spectral density both in source and reference plane are derived in tensor forms with the help of generalized paraxial Collins formula. By using the transmitting matrix law, we set up a general aligned ABCD optical system in order to analyze the propagation properties of beams passing through it. Numerical results show that intensity distribution in transversal output plane is easily influenced by coherence length in the source plane; oppositely it shows no variation by varying beam orders or dark-size adjusting parameter. We also investigate varying effects of two sorts of beam source parameters on degree of coherence in the transversal reference plane. Finally we show the relationship between dark-size adjusting parameter and paraxial transmitting intensity. Results show that when we decrease dark-size parameter to a certain number, the average intensity around the focal point disappear which is very different from ordinarily situation. All results in this paper may provide an effect way to describe and treat atom trapping and guiding by applying rectangular DHB.
In vivo study on middle ear bone ablation with pulse CO2 laser
Xianzeng Zhang, Xiaoyan Wang, Zhenlin Zhang, et al.
To evaluate the feasibility of middle ear bone ablation in-vivo with pulse CO2 laser. Healthy male New Zealand rabbits were used in the experiment. Middle ear mastoid bone of animal model was completely exposed by surgeon with conventional method, and then Pulse CO2 laser with a wavelength of 10.6μm and pulse lengths of about 10ms was used to carry out the opening surgery. Laser fluence was 8.3 J/cm2 with a repetition rates of 60 Hz, the beam diameter was 1.0 mm. After opening surgery, whole middle ear mastoid bone was obtained and processed with traditional histological method, the morphology changes and thermal damage around the opening window were examined by light microscope. Total operation time and light irradiation time were recorded. It showed that pulse CO2 laser is suitable for the fenestration operation in middle ear bone, and this no-touch technique not only can obtain the similar outcome as traditional methods, but also present a lot of advantages compared to the traditional methods. With the development of laser technology and the appearance of relative instruments, especially when the thermal damage was efficiently controlled, fenestration operation in ear with laser systems will be possible in near future.
Algorithm detecting the laser weak target with dynamic programming
Qingwei Ping, Guifen Xia
To solve the laser weak echo detection under the clutter background, a dynamic programming (DP) technique has been developed for the detection of weak targets. The primary advantages of DP are its sensitivity to weak targets along with its robustness to laser echo glitter. DP technology turn searching track of the target into the subsection optimization of the target. First, DP algorithm finds all track subsection of target. Second, these track subsections are synthesized into the potential track of target. Third, the track of the same target is combined. Then the detection outcome is found. Theory analysis and the simulated results indicate a sensitivity improvement of detection performance over conventional detection algorithm.
Theory of ballistic trajectory measurement using a multireflective laser light screen target
Jiyan Yu, Yongxin Li, Xiaoming Wang
A novel method of measuring flight trajectory for projectile was proposed. Seven light screen target (LST) was made up of two laser sources, two optical detectors and five pieces of mirror, which can measure the flight parameters including trajectory, direction and component velocity of three directions. The double Z-shaped LST was formed by laser light which was reflected by four pieces of parallel mirror, while the V-shaped LST was formed by laser light which was reflected by one piece of mirror. The cross points can be obtained by measuring the time when the projectile passing through every light screen. A principle experiment was done on a smooth plane table using a laser pen, four pieces of mirror and photodiode circuit by launching a steel ball. Velocity and position compare experiments were done simultaneously. The relative difference of velocity measurement was less than 0.2%. The difference of position measurement was less than 2mm. The results of velocity and position compare examination indicated the method proposed in this paper is feasible.
Research on the influence of optical properties of atmosphere to laser engineering application based on statistical characterization
Dong Chen, Bi-sheng Zhang, Yin-bo Huang, et al.
The complexity of the optical properties of atmosphere demonstrated in spatial and temporal characteristics causing the effect of optical properties on laser engineering could not be determined simply. It is necessary to reproduce the panorama of optical properties of atmosphere, and in this case the effect of optical properties on laser engineering could be evaluated. The survey of optical properties of atmosphere is continuous; facing zillions of data that changed instantaneously, the statistical method must be used while the original characteristic of optical properties of atmosphere in spatial and temporal distribution should be restored. Measurements of laser beam propagation in the atmosphere are taken. the wavelength is 0.946 μm and the transmission length is 2 kilometers. The data we achieved were made an hourly average, and then the same parameter based on each hour were made a monthly average, in this sense each parameter has 288 groups of data; the annual statistical characteristic value of different optical properties including atmospheric temperature, humidity, wind speed, visibility and the refractive-index structure parameter C2N were obtained. The molecular absorption, the aerosol particle scattering and extinction, the turbulence effects and the comprehensive effect of light propagation in the atmosphere were analyzed and evaluated for the atmospheric conditions in the whole year by using this method. The distribution and statistical characteristics of effects of atmosphere optical properties on the propagation were carried out. Analysis results show that, thorough understanding of the atmospheric optical properties in the application areas is very important to all kinds of laser engineering, including feasibility analysis of laser engineering, optical system design and performance evaluation. And statistical analysis method is an effective means to master the characteristics of complex system. It turns out that the effects of optical properties of atmosphere on the laser engineering is complicated and various, and a statistical method for a study of the analysis of the complex spatial and temporal distribution characteristics value is presented meanwhile.
Real-time measurement system of laser power in VC++
Hong-yan Zhuo, Ying-song Song, Lei Wang
ADLINK PCI-9114 multifunction data acquisition card, signal amplifier and multiplexer board and power sensor are used to establish the real-time measurement system of relative laser power. During producing laser, measuring and showing thermoelectric and photoelectric signal, calculating parameter and drawing the curve of relative power. Parameters of laser output power and energy are concerned with researchers. These parameters are important for evaluating laser system. In this paper, a real time laser power measure system is established. While laser system is operating, real time laser power measure system measured the power and energy of laser and plotted the waveform of relative laser power. The parameters such as pulse width, rise time, fall time, power integration, average power, peak power and average energy are computed.
SNR analysis of a new type of airborne three-dimensional gazing gating imaging laser radar system
Zhenmin Shen, Tian Lan, Yinchao Zhang, et al.
Signal to noise ratio (SNR) is a key parameter in laser radar system. In this paper, the principle and composition of a new type of airborne three-dimensional gazing gating imaging laser radar system are given. The signal model and the noise model have been established respectively according to the working process of the new type of laser radar. Then the SNR model has been built. Based on the SNR model, some important factors which influence the SNR have been analyzed. SNR can be improved by optimizing the system inherent parameters which include laser wavelength, laser pulse energy, receiving telescope diameter, the efficiency of launching and receiving optical system, and quantum efficiency of intensified charge-coupled device (ICCD). Moderately sacrificing system resolution and operating height can also improve SNR. It is shown by calculation and analysis that the most primary noise is the image intensifier quantum noise and other noises are negligible. Also SNR is almost unchanged with the increasing of the overall electron gain (G) in the whole actual range. Last the simplified SNR model is given according to the actual system parameters.
Improving range accuracy of rangefinders by combining reduction signal-detection threshold and correlation selection
Xuejun Wang, Zhongjian Li
This paper is a review of progress of laser rangefinders with digital signal processing. Correlation selection can be used with reduced signal-detection threshold for a determined distance. Time-of-flight method of measuring the range, by using in the detector channel a reduced signal-detection threshold for fixing the time position, in combination with correlation selection to distinguish the signal pulses on a background of an intense flux of noise spikes, are proposed for the possibilities of improving the detection and accuracy characteristics of pulsed laser rangefinders.
The investigation of Raman spectrum of water with gas (CH4, CO2) solution under 40MPa pressure at different temperatures
Xiao-feng Shi, Jun Ma
In order to understand how pressure, temperature and CH4 and CO2 molecules effect Raman spectrum of liquid water better, some experimental investigations of Raman spectrum of water with gas (CH4, CO2 and mixture of CH4 and CO2) dissolved are carried out at different temperature (up to 350°C) under high pressure (40MPa) and under different pressure (up to 40MPa) at room temperature using high-temperature and high-pressure set-up (top temperature is 350°C and top pressure is 40MPa). The band of the stretching vibration of water between 3000 and 3800 cm-1 has been studied. The results show pressure has little influence on Raman spectrum of water for all samples in our pressure variation range while temperature affects Raman spectrum of water significantly in the range room temperature to 350°C. Peak position, FWHM and the parameter R21 all vary sharply along temperature. As temperature is raised, peak positions shift to high frequency, FWHM decrease significantly and the parameters R21 increase with increasing temperature as EXP function in studied temperature range for all samples. All these variations have a relation with hydrogen bond. In addition, CO2 or CH4 dissolved in water makes all parameters vary along temperature more obviously and the CH4 molecule modifies the Raman spectrum of H2O much than the CO2 molecule.
Measurement capability improvement by enlarging beam divergence of moving police laser gun
Qian-jin Tang, Jie Shao, Zhi-zong Wu, et al.
Two laser guns with 2.95 mrad and 4.80 mrad beam divergence are designed to verify the relation of the measurement time, measurement distance, speed range, and beam divergence. The on-the-road test result shows that 4.80 mrad beam divergence is better than 2.95 mrad when measuring vehicle speed within 60 to 150 km/h at a distance 80~150 m, which indicates that appropriately enlarging the beam divergence can extend active area and increase measurement speed range.
The research of synthetic aperture digital holography for long-working-distance microscopy
Feng Pan, Wen Xiao
A method of digital holography for high-resolution microscopy at long working distance is proposed using a synthetic aperture. A series of digital holograms covered different spatial frequency ranges of an object optical field are recorded by using different tilted object illuminations. Subsequently, the intensity images are numerically reconstructed and magnified respectively. Finally, a synthetic image with the resolution improved and speckle noise suppressed is obtained by synthesizing these reconstructed images. The results show that the proposed method can be easily used to in-situ microscope at a long working distance.
High-speed laser photoacoustic imaging system combined with a digital ultrasonic imaging platform
Lvming Zeng, Guodong Liu, Xuanrong Ji, et al.
As a new field of combined ultrasound/photoacoustic imaging in biomedical photonics research, we present and demonstrate a high-speed laser photoacoustic imaging system combined with digital ultrasound imaging platform. In the prototype system, a new B-mode digital ultrasonic imaging system is modified as the hardware platform with 384 vertical transducer elements. The centre resonance frequency of the piezoelectric transducer is 5.0 MHz with greater than 70% pulse-echo -6dB fractional bandwidth. The modular instrument of PCI-6541 is used as the hardware control centre of the testing system, which features 32 high-speed channels to build low-skew and multi-channel system. The digital photoacoustic data is transported into computer for subsequent reconstruction at 25 MHz clock frequency. Meantime, the software system for controlling and analyzing is correspondingly explored with LabVIEW language on virtual instrument platform. In the breast tissue experiment, the reconstructed image agrees well with the original sample, and the spatial resolution of the system can reach 0.2 mm with multi-element synthetic aperture focusing technique. Therefore, the system and method may have a significant value in improving early detecting level of cancer in the breast and other organs.
The effectiveness of percutaneous laser disc decompression for the prolapsed lumbar intervertebral disc
Ming Wei Mu, Wei Liu, Wei Feng, et al.
Objective: to investigate the role of associated factors in the effectiveness of laser treatment for prolapsed lumber intervertebral disc. Method: 302 prolapsed lumber intervertebral discs in 212 patients were treated with percutaneous laser disc decompression (PLDD). Patients were followed up by 12month, the associated factors which affecting the effectiveness of treatment, ie age, duration of illness were analyzed. Results: Punctual Success rate was 100%. After 12 month's follow up, 86% successful outcomes were obtained, in which 93% successful outcomes were obtained in patients less than 50 years old, 92% successful outcomes was obtained in the patients whose duration of illness less than 1 year.
Time-delay compensation in data-acquisition process for rotational Raman lidar
Weiguo Kong, Siying Chen, Yinchao Zhang, et al.
Pure Rotational Raman Lidar is a recently developed method for atmospheric temperature detection. Since the Raman-scattering-signals are very weak, the photon-counting method is employed, which could be achieved by using a multiscaler. Time delays, which exist among the trigger channel and the two count channels of the multiscaler, will affect the corresponding relationship between the detected signals and the actual altitudes where the signals are returned, so it is necessary to make some compensation. However, it is difficult to measure the time delays with traditional instruments such as oscillograph, for there is no access to the final internal trigger signal or count signals. In this paper, a measuring system is established, with a Digital Delay/Pulse Generator as the chief component, which is not usually used as a measuring instrument. The measurement precision could reach about 50ps. Meanwhile, the compensating method is also provided to improve the positioning accuracy of the lidar system.
Stability of a distributed feedback fiber laser sensor array with unequal wavelength spacing
Tuan-wei Xu, Fang Li, Yue-feng Wu, et al.
A 16 channel distributed feedback fiber laser sensor array is reported. The spacing of neighbor lasers is 100 GHz and 200 GHz in turn. Compared with grating sideband reflection, Rayleigh backscattering from ~24 m long passive fiber is more responsible for the instability, and it's found that increasing the reflection of grating could reduce the sensitivity of DFB FL to Rayleigh backscattering.
Thin gas cell with GRIN fiber lens for intra-cavity fiber laser gas sensors
Mo Li, Jing-min Dai, Gang-ding Peng
Fiber laser gas sensors based on the intra-cavity absorption spectroscopy require the use of gas cells. We propose a simple and reliable gas cell using graded-index fiber lens (GFL) based all-fiber collimator. Conventional gas cells usually utilize direct fiber-to-fiber coupling without collimators or graded-index (GRIN) lens as collimators. Direct fiberto- fiber gas cell has simple configuration, but it suffers from high coupling loss and stray light interference. Gas cells applying fiber pigtailed GRIN lens are advantageous to achieve low coupling loss. However, fiber pigtailed GRIN lens requires accurate and complicated alignment and glue packaging which could compromise long term reliability and thermal stability. The proposed technique fabricates all-fiber collimators by simply splicing a short section of gradedindex fiber to single mode fiber which is both compact and durable. With that collimator, the gas cell can be fabricated very thin and are suitable for extreme environments with high temperature and vibration. In this paper, we have carried out experiment and analysis to evaluate the proposed technique. The coupling efficiency is studied versus different GFL gradient parameter profiles using ray matrix transformation of the complex beam parameter. Experiments are also done to prove the practical feasibility of the collimator. The analysis indicates that gas cell using GFLs can overcome the disadvantages of traditional design; it may replace the conventional gas cells in practical applications.
Pose measurement method with six parameters for microassembly based on an optical micrometer
Xin Ye, Qiang Wang
This paper presents a new pose measurement method of microminiature parts that is capable of transforming one dimension (1D) contour size obtained by optical micrometer to three dimension (3D) data with six parameters for microassembly. Pose measurement is one of the most important processes for microminiature parts' alignment and insertion in microassembly. During the past few years, researchers have developed their microassembly systems focusing on visual identification to obtain two or three dimension data with no more than three parameters. Scanning electronic microscope (SEM), optical microscope, and stereomicroscope are applied in their systems. However, as structures of microminiature parts become increasingly complex, six parameters to represent their position and orientation are specifically needed. Firstly, The pose measurement model is established based on the introduction of measuring objects and measuring principle of optical micrometer. The measuring objects are microminiature parts with complex 3D structure. Two groups of two dimension (2D) data are gathered at two different measurement positions. Then part pose with 6 parameters is calculated, including 3 position parameters of feature point of the part and 3 orientation parameters of the part axis. Secondly, pose measurement process for a small shaft, vertical orientation determination, and position parameters obtaining are presented. 2D data is gathered by scanning the generatrix of the part, and valid data is extracted and saved in arrays. A vertical orientation criterion is proposed to determine whether the part is parallel to the Z-axis of the coordinate. If not, 2D data will be fixed into a linear equation using least square algorithm. Then orientation parameters are calculated. Center of Part End (CPE) is selected as feature point of the part, and its position parameters are extracted form two group of 2D data. Finally, a fast pose measurement device is developed and representative experiments are carried out. Results show that the measurement method could obtain pose of complex 3D micro parts fast and accurately, and can meet the demand of microassembly system.
Comparative research on femtosecond laser and nanosecond laser induced damage to CCD
Jing-jing Dai, Zhi-yong Wang
The contrastive damage experiments of CCD irradiated by 800nm femtosecond laser with the pulse duration of 330fs and 1064nm laser with the pulse duration of 10ns were studied from the energy density and power density. The failure problems of the CCD devices irradiated by the two kinds of laser pulses were studied. The experimental results show that the failure threshold of CCD irradiated by femtosecond laser is 2.3 nJ / cm2 and it is 3~4 order lower than that by nanosecond laser. According to the micro-analysis of CCD, it is found that the damage takes place at the light activated elements.
Reduction of speckle noise in digital holography by multiple holograms
Lu Rong, Wen Xiao, Feng Pan
In this paper, we introduce and demonstrate a new method of reducing speckle noise by multiply holograms. It can utilize both the phase and amplitude information of the object wave-front. In the superposition process, the phase surfaces with high signal to noise ratio in the different phase images have been appropriately weighted according to reconstructed intensity image. We show a theoretical justification of the procedure and experimentally-obtained results of a USAF-1951 resolution test target, both of which demonstrate that the proposed method could reduce the speckle noise effectively, and improve the resolution of reconstructed image.
A novel approach for LIBS enhancement of cations underwater
Yuan Lu, Ying Li, Jiang-lai Wu, et al.
Laser Induced Breakdown Spectroscopy (LIBS) has been developing as a promising technique with many advantages, including on-line, real time, stand off and multi-element detection etc. At present, LIBS application has involved many areas; more and more researchers have studied LIBS as an in-situ measurement for oceanic sensing. In this paper, a novel approach for LIBS enhancement has been introduced and used to improve the sensitivity of underwater detection. In this approach, the replacement reaction assisted with the electric field was utilized to strengthen the reaction and increase local cations concentration for depositing on the underlay surface. With the aid of replacement reaction and electric field, the LIBS sensitivity for cations detection underwater was found to be enhanced significantly, hence the detection limit. The detection limit of 16 ppb was achieved for copper cations (Cu2+) detection in the water solution of CuSO4. The obtained results suggested that this novel approach has great potential to be developed as an effective method for cations detection underwater.
High-sensitive monitoring of carbon monoxide in industry flue gases using tunable diode lasers
Zhi-rong Zhang, Feng-zhong Dong, Hua Xia, et al.
Carbon monoxide (CO) is a very important gas generated in the industrial process; therefore to implement CO concentration on-line monitoring is a key factor for industrial process control. Tunable diode laser absorption spectroscopy (TDLAS) is a high sensitive, high selective and fast trace gas detection technique. With the features of tunability and narrow linewidth of distributed feedback (DFB) laser and by precisely tuning its wavelength to a single isolated absorption line of the gas, TDLAS technique can be utilized to accurately perform online gas concentration monitoring with very high sensitivity. In this paper, a system for online monitoring of CO concentration is developed by our group employing TDLAS technique. The experimental results are present and discussed in this report. The characteristics of the system are: the sensitivity, 10ppm; detection accuracy, 0.02%; long term stability, 1%.
An improved reconstruction algorithm by direct discretization in digital holography
Yizhuo Zhang, Dayong Wang, Changgeng Liu, et al.
Digital holography combines the advantages of the optical holography and the digital image processing as a method for recording and reconstructing amplitude and phase of a wave field. Traditional reconstruction algorithms can only obtain image with the fixed pixel size. By directly discretizing the Reyleigh-Sommerfeld (RS) integral formula, a new reconstruction algorithm is proposed. Experiment result shows that the reconstruction pixel size and pixel number can be controlled with the proposed algorithm.
Corona solar blind ultraviolet image detecting method
Li-min Yin, Wen-qing Tang, Yu Zhang
Corona is one of important reasons of electrical energy loss in the electric power. According to incomplete statistics, corona loss electrical energy has achieved two thousands and fifty millions kW.h in our nation every year. Sometimes corona also can have some disturbance to radio and communication. Therefore to discover and examine corona promptly has the extremely vital significance for conserving energy and realizing high quality communication. Ultraviolet image detecting technology is a preferred corona detection method in electric power. It may realize all-weather reliable survey to corona. The solar blind ultraviolet signal discharged by corona is quite weak. Moreover the ultraviolet image quality has been affected seriously by the detection system noise. A corona solar blind ultraviolet image processing method is proposed in this paper. Ultraviolet image has so small target, low contrast image, district characteristic and real-time demand that it is processed by multi-scale ultraviolet morphology filter technology based on mathematics morphology in this paper. Results show that the method can stretch image contrast, enhance target and weaken noise. The algorithm is easy to deal in parallel and it can be realized easily by hardware. It will be accurately demarcated when the condition of device need to be absolutely measured. The paper proposes a kind of mathematics morphology algorithm. Solar blind ultraviolet image will be further processed according to temperature and humidity in order to remove the infection of corona discharge demarcation and solve correct demarcation question when equipment condition need to be absolutely measured.
Imaging characteristics of a volume holographic lens
Jing Yang, Zhu-qing Jiang, Zhi-qiang Xu, et al.
A volume holographic grating lens can reconstruct the three-dimensional information by conducting multiple optical slicing of an object based on Bragg selectivity of the volume holographic grating. In this paper, we employ the point-spread function of volume holographic imaging system to theoretically analyze its imaging resolution. In the experiments, the volume holographic gratings are made with a spherical reference (SR) and a planar reference (PR), respectively, and used as volume holographic imaging lens in our imaging system. The longitudinal and lateral defocusing characteristics of volume holographic lens with SR and with PR are investigated experimentally by displacing the interested objects from original reference location, respectively. The effects of the parameters of the volume holographic lens on the longitudinal and lateral resolution are also discussed. The experimental results show that increasing the size of the volume holographic lens can improve the depth resolution, and in particular, it has greater influence on SR VHI. The lateral selectivity of SR VHI is more sensitive than that of PR VHI, and the Bragg degenerate diffraction of PR VHI on the y axis is obviously observed.
Depth-resolved imaging by using volume holograms
Zhiqiang Xu, Zhuqing Jiang, Jing Yang, et al.
In this paper the reconstructing images of a tiny object with a volume hologram are investigated by examining the effect of Bragg mismatch on the quality of imaging. The imaging depth resolutions of the volume holograms with the different radii are compared. Furthermore, the simultaneous imaging ability of the volume holographic gratings for the different depths of the object space is demonstrated experimentally by recording two holographic gratings in the same material. The results show that the depth resolution of the VHI system is 2.1mm in our experiments, in which a volume hologram is recorded in a 2-mm-thick LiNbO3:Fe:Cu crystal with two recording beams interfering at the wavelength of 532nm, and is located at a working distance of f=75mm away from the object lens.
Measurement of temperature field in the region near to the radiator by using digital holography
Yan Li, Dayong Wang, Guangjun Wang, et al.
A simple method for measurement of temperature field in the region near to the metal plate of the radiator is demonstrated by using digital holography in the Lensless Fourier transform configuration (LFT). The temperature is measured within the boundary layer of the convective flow field. The deviation of the temperature produced by this method, from that obtained by the thermocouple is rather small. It has shown that the method is reasonable and efficient.
Study on testing device of pulse laser range equipment
Yong Zhang, Wei-qi Jin
Electro-optical testing device is the important technical means to guarantee the operation efficiency of laser range equipment in complex battle environment. Several important indexes must be tested to ensure the good operation of pulse laser range equipment, such as the collimation of optical axes, the maximal measuring distance, laser emitting energy, resolution capability, and laser spot quality. A new kind of testing device is provided in paper. On the one hand, delay simulating space distance by computer and quasi-laser is used in the term of testing electrical parameters. The testing method is to collimate the emitted laser beam and disperse the beam into a photometric sphere. Then, emit with a regulated temporal delay a new beam into the receiver module of the laser range finder, which can realize automatic, fast and non-disassembly testing to electrical parameters. On the other hand, a new kind of infrared-detecting transforming device based on up-conversion effect is used in the term of testing laser spot characteristics, which can realize the capturing of laser spot in real-time to the pulse laser range finder and high-frequency pulse laser measuring range system. Applications show the testing device is automatically and quickly for many kinds of laser range finder, which has the characteristics of compact structure, portability, high reliability, which is especially suitable to the application under field operations.
Optical systems design used for laser smoothing in far field
Xianying Ge, Tian Lan, Yinchao Zhang, et al.
Laser smoothing technology is employed not only in near field but also in far field in order to make images of scenes on the ground on the basis of echoes in systems such as 3-D imaging lidar. In this paper, the principle of superposition after partition is described in detail. Two methods for laser smoothing are introduced, one of which is lens array, capable of attaining a large area of uniform illumination in far-field, and the other one is birefringent lenses, suitable to obtain a small area of uniform illumination in far-field. A comparison is made about the performance characteristics of the two methods from different aspects. This provides a reference about how to choose smoothing methods to achieve uniform irradiation.
Numerical study of reflection imaging technique for measurement of optical nonlinearity
Qijing Cai, Junyi Yang, Yinglin Song
A single-laser-shot reflection imaging technique, which can measure the nonlinear optical refraction of the surface of material possessing limited transparency, is present. Using the model of the reflection 4f coherent imaging system with phase object, we analyze the phase and amplitude characteristics of the beam reflected from the interface. With the help of computer and MATLAB, we have done some theoretical analysis and got some conclusions including advantages and disadvantages. Our model and its corresponding simulation is presented in order to validate our approach.
An improved sub-pixel algorithm for laser spot center determination based on Zernike moments
Kun Zhang, Hai-qing Chen, Jun Li, et al.
The laser spot determination is the critical technique in laser detecting systems. Due to atmospheric turbulence and other factors, the laser spot intensity distributes unevenly in the long-distance measurement. In order to improve the location precision of the laser spot detection, an improved sub-pixel algorithm based on Zernike moments is presented in this paper with theoretical analysis. The experimental results of the proposed algorithm with CCD image test are also given and compared with that of four conventional algorithms including gravity model, Hough transform, circle fitting, and spatial moment operators. The comparative results demonstrate that the improved algorithm based on Zernike moments has the virtue of higher measuring precision. The stability and interference suppression ability are also improved. The proposed algorithm has already been applied into the processing of our laser detecting system, which can also play an important role in automatic recognition, etc.
30KW peak power flash-lamp pumped pulsed static Nd:YAG solid-state laser with one cavity
Xue-sheng Liu, Sun Yao, Ying-hau Cao, et al.
A high energy high peak power flash-lamp pumped pulsed Nd:YAG solid-state laser is investigated in this paper. The symmetrical resonator laser is developed and rated at single pulse energy 60J, peak power 30KW with beam parameter product 2mm.mrad. The total system electro-optics efficiency of the lamp-pumped YAG laser is as high as 3.1% with pulse width tunable between 0.05-2ms. The results are consistent with the theoretical analysis and simulation.
The effects of turbulent aberrations on an optical communication system based on orbital angular momentum-carrying beams
Yi-xin Zhang, Jian-cai Xu, Jian-yu Wang, et al.
A photon communication system based on orbital angular momentum (OAM)-carrying beams is studied. We compartmentalize the atmospheric aberration into tilt,coma, astigmatism as well as defous. We numerically analyze the effects of tilt on the orbital angular momentum of communication beams and find that the tilt aberration can induce the noisy OAM. With the increasing of parameters P, L, the probability of initial OAM goes down while the effective number of noise OAM increases. At the same time, the peaks of the induced OAM probability (max-probability) are different as the P, L, changes. The increase of zenith angle damages the probability and leads to noisy OAM. This can also be applied to the impact of refractive index structure parameter. We also numerically analyze the effects which receiving-radius puts on the receiving probability of initial OAM through tilt aberration. Under the influence of tilt, the receiving probability of previous orbital angular momentum slashs with the receiving-radius becoming large.
Near-optimal focus for Gaussian beam propagation through turbulence: analysis and wave optics simulation results
Xifeng Xiao, David Voelz
We recently proposed a metric that incorporates scintillation reduction and beam spread for evaluating the performance of a partially coherent laser beam propagating through atmospheric turbulence. The metric was evaluated relative to other measures such as probability of fade and number of fades and it was verified that the metric can be used to find the parameters for optimal or near-optimal beam performance. In this work, we review the performance metric and develop analytical expressions as a function of the source beam curvature F0 and other link parameters. The behavior of the metric as a function of F0 is investigated for different link scenarios. A wave (physical) optics simulation is also implemented and its results compare favorably with the analytical results.
Third-order nonlinear properties of [PbPc (CP) 4] at 600nm wavelength
Several heavy mental substituted phthalocyanines are effective materials for optical limiters in the visible and near IR. Lead-tetrakis (cumplphenoxy) phthalocyanine [PbPc (CP)4] was identified as especially attractive for optical limiting applications. In the paper, we investigate the third-order optical nonlinearities of [PbPc (CP) 4] at 600nm by a nonlinear-imaging technique with a phase object (NIT-PO). The theoretical simulation fit well with experimental results.
Influence of incident angle on the decoding in laser polarization encoding guidance
Muchun Zhou, Yanru Chen, Qi Zhao, et al.
Dynamic detection of polarization states is very important for laser polarization coding guidance systems. In this paper, a set of dynamic polarization decoding and detection system used in laser polarization coding guidance was designed. Detection process of the normal incident polarized light is analyzed with Jones Matrix; the system can effectively detect changes in polarization. Influence of non-normal incident light on performance of polarization decoding and detection system is studied; analysis showed that changes in incident angle will have a negative impact on measure results, the non-normal incident influence is mainly caused by second-order birefringence and polarization sensitivity effect generated in the phase delay and beam splitter prism. Combined with Fresnel formula, decoding errors of linearly polarized light, elliptically polarized light and circularly polarized light with different incident angles into the detector are calculated respectively, the results show that the decoding errors increase with increase of incident angle. Decoding errors have relations with geometry parameters, material refractive index of wave plate, polarization beam splitting prism. Decoding error can be reduced by using thin low-order wave-plate. Simulation of detection of polarized light with different incident angle confirmed the corresponding conclusions.
Sensitive measurement of optical nonlinearities of ZnSe based on a phase object
Chang Wei Li, Yu Xiao Wang, Min Shui, et al.
A nonlinear image technique for characterization of the optical nonlinearities is used to investigate the solid semiconductor ZnSe at 600 nm. The method based on a 4f nonlinear image technique with a phase object is used to obtain the diffraction pattern of the nonlinear filter in solid ZnSe located at the Fourier plane by a CCD camera. The nonlinear absorption coefficient and nonlinear refraction index were both obtained by fitting the nonlinear image. Good agreement between the experiment data and the simulated result are obtained indicating a sensitive and powerful method for nonlinear optical measurements.
Optical image encryption based on two-dimensional N-parameter fractional Fourier transform
Haiying Zhang, Qiwen Ran, Yu Xiao, et al.
In this paper, the weighted fractional Fourier transform with dilation parameter (N-PFRFT) is proposed as the weighted combination of the first four integer-order ordinary Fourier transforms. This N-PFRFT is an extension of four-item weighted fractional Fourier transform (N-PFRFT) defined by Shih[1] and it owns four free parameters in the weight coefficients besides the order of the fractional Fourier transform. A novel image encryption algorithm is presented by the N-PFRFT.The method owns more secret keys than the encryption methods operated by other fractional Fourier transforms without any increase of the computational complexity. On the other hand, the image still can't be decrypted correctly even though the order of FRFT which is treated as a secret key is known. So do the four free parameters. Therefore, both the order parameter and the vector parameter can be chosen in the real domain to improve the security of the encryption method. Digital simulations are presented to verify the more validity and efficiency of the algorithm.
Target detection and recognition techniques of line imaging ladar sensor
Zhi-hui Sun, Jia-hao Deng
A line imaging ladar sensor using linear diode laser array and linear avalanche photodiode (APD) array is developed for precise terminal guidance and intelligent proximity fuzing applications. The detection principle of line imaging ladar is discussed in detail, and design method of the line imaging ladar sensor system is given. Taking military tank target as example, simulated tank height and intensity images are obtained by the line imaging ladar simulation system. The subsystems of line imaging ladar sensor including transmitter and receiver are designed. Multi-pulse coherent algorithm and correlation detection method are adopted to improve the SNR of echo and to estimate time-of-flight, respectively. Experiment results show that the power SNR can be improved by N (number of coherent average) times and the maximum range error is 0.25 m. A few of joint transform correlation (JTC) techniques are discussed to improve noncooperative target recognition capability in height image with complex background. Simulation results show that binary JTC, non-zero-order modified fringe-adjusted JTC and non-zero-order amplitude-modulated JTC can improve the target recognition performance effectively.
Sensitive measurement of rotational lifetime of toluene using time-resolved 4f imaging technique
Xiao Jin, Min Shui
Using time-resolved pump-probe system based on nonlinear image technique with phase object, we determine the rotational lifetime of toluene with 19-ps laser pulse at 532 nm. The system can be applied to both degenerate and non-degenerate beams in any polarization states. The proposed method is advantageous and imposes a lower stress in the cases of fragile materials, since a single shot of laser pulse is enough for the definition of their nonlinear refractive indices and absorption coefficients. Advantages of this scheme are relative ease of producing the steady probe beam with top-hat profile. The coupling theory of the pump beam and the probe beam in perpendicular linear polarizations states is used to interpret the experimental results. With the help of coupling equations we numerically fitted our experimental results. Good agreement is obtained between the theory and the experiment. Additionally, we derive the rotational lifetime of toluene τrot=4.8 ps with the help of theoretical fit.
Contrastive study on two kinds of semiconductor saturable absorber mirrors for side-pumped passively mode-locked Nd:YAG lasers
Qiao Wen, Liqun Sun, Yonggang Wang, et al.
Based on the reflectance of saturable absorber depended on the optical intensity and the interference theory, we investigate the reflectance bandwidth characteristic of the semiconductor saturable absorber mirror (SESAM). Two kinds of SESAMs, one of which satisfies the antiresonance condition, and the other does not, are contrastively studied in mode-locked Nd:YAG lasers. Results show that stabilized continuous-wave mode-locking can also be obtained in picosecond regime by the SESAM, which dose not fulfill the antiresonance condition, as good as the results obtained using a mature commercial SESAM satisfying the antiresonance condition. Because the bandwidth of picosecond regime mode-locked pulse is not broad; therefore a broad bandwidth and a minimal group velocity are not necessary. Without considering the limit of the antiresonance condition, the difficulty of designing and growing SESAMs will be decreased significantly and there will be more freedom in the macroscopic parameters.
Application of microscopic image dynamic range enhancement in sputum smear tuberculosis intelligent examination
Ping Zhong, Nian Luo, Chen-jie Song
The bacteriological microscopic examination of sputum smear for tuberculosis is the most important means of diagnosis and experiments for tuberculosis. Through micro-imaging systems, machine vision systems, digital image processing and computer pattern recognition technology, dynamic intelligent recognition and counting of TB-DNA could be realized. However, the dynamic range of CCD image sensor is limited. The information of TB-DNA could not be fully recorded on microscopic image. In this paper, an effective method to extend the image dynamic range through merging multiple exposure images is proposed. The microscopic images of the same scene with different exposure are taken by rotating the disk-shaped optical grads attenuator that installed under the objective lens of microscopic system to control the illumination. These different exposure images are processed firstly to get irradiance response function of the imaging system, and then the high dynamic range microscopic image (HDRMI) could be obtained. Through the mapping algorithm the dynamic range of HDRMI is compressed in order to been displayed on the general display devices, which not only highlight the feature information of bacillus but also maintain the overall contrast of original microscopic image. The method proposed can effectively express the image information of the bright areas and dark areas in the scenes and enhance the image details and color characteristics. The quality of micro-imaging systems is improved. It is proved that the method proposed in the paper can enhance the resolution and stability of the TB image recognition through the experiment.
Coordinates calibration method in a robotic remanufacturing measurement system based on linear laser scanner
C. D. Shen, S. Zhu, C. Li, et al.
In robotic remanufacturing measurement system, the 3D laser scanner is arranged by the robot and the object scanned is mounted on a turntable. This paper deals with the method of calibrating the relationship between the scanner coordinate and the robot Tool0 and furthermore locating the center axis of the turntable. The data of Tool0 can be directly obtained denoting its relationship with the robot base coordinate. So, the new methods of coordinate's transformation are effectively developed. Moreover some motivated experiments and optimized programs are designed for realizing process stabilization and reliability. This paper detailed explains the basic algorithm theory, practical operation instructions, the experiment data analysis, and etc. Theory deduction and experiments show the new methods are reasonable and efficient.
Probing of cancer cell apoptosis by SERS and LSCM
Jian Kang, Huaimin Gu
Surface enhanced Raman spectroscopy (SERS) can provide information of internal structures and chemical components from different kinds of samples. Laser scanning confocal microscopy (LSCM) can show morphologic information of samples by high-resolution optical images with different focal planes. In this paper, the dynamic variation of cancer cells (HELA cells) in the apoptosis was first studied by combining SERS and LSCM. After gold nanoparticles (GNPS) uptake, HELA cells were divided into two groups, and were respectively studied at six different time points of cell apoptosis period by SERS and LSCM. The LSCM images of HELA cells obtained at different time points were analyzed, and the morphology varieties of HELA cells apoptosis were obtained. It suggests that HELA cells apoptosis gradually in the apoptosis period until they died. In addition, Raman spectra of HELA cells measured at different time points were also compared. It shows that some Raman signal peaks shift, and FWHM of Raman peaks change too. The variation of internal structures and chemical constituents were analyzed according to the shifts and FWHM of the Raman peaks. The internal dynamic information and morphologic varieties from HELA cells apoptosis gained by combining SERS and LSCM will make us to understand cancer cell apoptosis throughly.
Two-micron solid state master oscillator and fiber power amplifier
Jing Li, Suhui Yang, Junna Guan, et al.
Development of 2 micron solid-state lasers has attracted a great deal of attention in recent years, because 2 micron lasers have many potential applications in various fields, such as remote sensing, medical application, laser radar, and optical communication in space. The MOPA system is an effective way to obtain high energy and good frequency and beam qualities which are required in coherent lidars. The traditional MOPA systems use injection seeding technology to obtain narrow linewidth and high power/energy laser output at the same time. Feedback control makes systems of injection seeding MOPA more complicated in applications. Thanks to the fast development of fiber fabrication technology, various fibers working in 2 micron region are commercially available. Two micron fiber MOPA systems are more attractive for researchers due to their compactness, good thermal dissipation and high efficiency. A 2 micron master-oscillator-power-amplifier (MOPA) system was built. The seed oscillator was a plano-concave straight cavity. YAP Laser crystals with 4% and 5% thulium-doped concentration were used in our experiments. 1.5% and 3% output couplers were used. 442mW output power at 1.99μm was obtained with the 4% thulium-doped Tm:YAP crystal when the launched pumping power is 2.7W. The seed oscillator is coupled into a 4.5-meter-long double-cladding LMA Tm3+ and Al3+ co-doped fiber. The fiber diameter is 25 μm and NA is 0.1. 6.13W CW amplified output signal power was obtained when the launched pumping power was 60W.
A method for three-dimensional quantitative observation of the microstructure of biological samples
Pengfei Wang, Dieyan Chen, Wanyun Ma, et al.
Contemporary biology has developed into the era of cell biology and molecular biology, and people try to study the mechanism of all kinds of biological phenomena at the microcosmic level now. Accurate description of the microstructure of biological samples is exigent need from many biomedical experiments. This paper introduces a method for 3-dimensional quantitative observation on the microstructure of vital biological samples based on two photon laser scanning microscopy (TPLSM). TPLSM is a novel kind of fluorescence microscopy, which has excellence in its low optical damage, high resolution, deep penetration depth and suitability for 3-dimensional (3D) imaging. Fluorescent stained samples were observed by TPLSM, and afterward the original shapes of them were obtained through 3D image reconstruction. The spatial distribution of all objects in samples as well as their volumes could be derived by image segmentation and mathematic calculation. Thus the 3-dimensionally and quantitatively depicted microstructure of the samples was finally derived. We applied this method to quantitative analysis of the spatial distribution of chromosomes in meiotic mouse oocytes at metaphase, and wonderful results came out last.
Analysis of quantitative phase detection based on optical information processing
Wang Tao, Jiang-Chen Tu, Kuang-Tao Chun
Phase object exists widely in nature, such as biological cells, optical components, atmospheric flow field and so on. The phase detection of objects has great significance in the basic research, nondestructive testing, aerospace, military weapons and other areas. The usual methods of phase object detection include interference method, grating method, schlieren method, and phase-contrast method etc. These methods have their own advantages, but they also have some disadvantages on detecting precision, environmental requirements, cost, detection rate, detection range, detection linearity in various applications, even the most sophisticated method-phase contrast method mainly used in microscopic structure, lacks quantitative analysis of the size of the phase of the object and the relationship between the image contrast and the optical system. In this paper, various phase detection means and the characteristics of different applications are analyzed based on the optical information processing, and a phase detection system based on optical filtering is formed. Firstly the frequency spectrum of the phase object is achieved by Fourier transform lens in the system, then the frequency spectrum is changed reasonably by the filter, at last the image which can represent the phase distribution through light intensity is achieved by the inverse Fourier transform. The advantages and disadvantages of the common used filters such as 1/4 wavelength phase filter, high-pass filter and edge filter are analyzed, and their phase resolution is analyzed in the same optical information processing system, and the factors impacting phase resolution are pointed out. The paper draws a conclusion that there exists an optimal filter which makes the detect accuracy best for any application. At last, we discussed how to design an optimal filter through which the ability of the phase testing of optical information processing system can be improved most.
Laser scattering properties of the rough ellipsoidal object with the random facet model
Jing Guo, Chun-ping Yang, Mei-ling Kang, et al.
Laser scattering properties are studied from the rough surface of an ellipsoidal object with the random facet model and the electromagnetic scattering theory. For actual ellipsoidal objects, such as some airships and air balloons, their lateral correlation lengths are usually longer than the incident laser wavelength 1.06μm, and their surfaces are conventionally the Lambertian surface. Hence, it is feasible to analyze their laser scattering properties of the ellipsoidal object by means of the random facet model. In order to evaluate the scattering, firstly, the ellipsoidal surface is decomposed into many facets according to axial symmetry, then scattered intensity can be denoted for every facet with a laser scattering model of the Lambertian surface. Secondly, total intensity received by a far-field optical detective system is gained with the incoherent superposition principle for all facets, where an incident shadow function and a scattering shadow function are introduced. In the end, far-field angular distribution of the laser scattering intensity is computed and analyzed under different conditions. The numerical results suggest that the laser backscattering intensity of the ellipsoidal object increases with its surface roughness. However, if the ellipsoidal surface is correspondingly rough, the incident laser power might be scattered around.
The optical monitor system of anti-phobic raid underwater
Chengdong Zheng, Yan-sheng Weng, Xi-zhan Liu
The underwater security system, used in the Qingdao sailboat game of 2008 Olympic Games, combined multiple underwater cameras with sonar detectors, forms an underwater barrier, which can observe the movement of suspicious objects and get the underwater video images continuously and instantly. The lighting system can provide sufficient illumination matched with target to reach the best imaging result. The whole system with the function of centralized control, depth measurement, leakage alarm and image processing, is the original equipment in domestic underwater antiterrorism optical research area.
Experimental and simulation research on micro-Doppler effect in laser coherent detection
Bi-da Su, Su-hui Yang, Jing-feng Wang, et al.
Micro-Doppler effect and its mathematical model were discussed. The Micro-Doppler effect of vibration and rotation of moving point target were analyzed. The micro-Doppler frequency shift induced by vibration is simulated and proceeded by means of the time-frequency analysis. A micro-Doppler Solid-state coherent ladar system for detecting micro-motion of target was demonstrated to detect the micro-Doppler frequency shifts induced by vibration, complex micro motion and rotation, and the micro-Doppler frequency shift induced by rotations at 0.2 r/s or vibrations at 0.5Hz were detected. The information of micro-motion was extracted by the arithmetic of time-frequency analysis. These results are helpful for target's feature extraction and identification.
Irradiance scintillation on laser beam propagation in the near ground turbulent atmosphere
Xi-wen Qiang, Jian-ping Song, Jian-wei Feng, et al.
Optical scintillation degrades beam quality as laser beams propagation in the atmosphere and increases rates of code-error for high-data-rate laser communication in the atmosphere. The scintillated irradiance depends on integrals of atmospheric turbulence strength along the propagation path. For the shorter path-length and weaker atmospheric turbulence, the integral is smaller, and the Rytov weak fluctuation theory can solve the problem successfully. However, for longer path-length and/or stronger atmospheric turbulence strength, multiple scattering events must occur and result in saturation of irradiance scintillation. The irradiance scintillation of laser beams propagation in the near ground turbulent atmosphere is investigated for the case of plane wave and spherical wave at various typical atmospheric turbulence strengths and inner scale of atmospheric turbulence. The dependence of irradiance scintillation on turbulence strength, path-length, and inner scale is presented for the plane wave case and spherical wave case. The results on plane wave case and spherical wave case are compared.
Experimental research on laser micro-Doppler effect for detecting vibration properties of a moving target
A detection system based on the laser micro-Doppler effect for detecting vibration-properties of moving target was developed. This system can detect the micro-Doppler effect induced by vibration whose order of magnitude is micrometer well. Frequency domain analysis and time-frequency joint analysis of experimental results showed that the complex vibration of target can be effectively detected by laser micro-Doppler effect, and also the application range of laser micro-Doppler effect is further extended. The results of feature extraction indicate that time-frequency analysis method is fit for the analysis of time-varying micro-Doppler signal, and the vibration signature of the moving target can be effectively extracted. The experimental results are shown that it confirms the efficiency of this system.
Design of an optical fiber-grating spectrum-dividing system for NO2-DIAL
Ben Xu, Kai Yang, Dawei Fang, et al.
Differential Absorption Lidar for detecting atmospheric NO2 (NO2-DIAL) is used extensively for its high precision and spatial resolution, and the measurement can be done real-time with a wide range. The design of spectrum-dividing system is a key component of lidar. According to characters of DIAL, such as adjacency of laser wavelength and weakness of received signal, a set of optic fiber-grating spectrum-dividing system is developed. The system has the advantages such as high spectral resolution, efficiently divide lidar echo signals in different wavelengths, weak attenuation, receive and process signals in two channels synchronously, etc. So the SNR of receiving system has improved.
Weak signal detection system and noise analysis for aerosol detection lidar
Zong-jia Qiu, Si-ying Chen, Yin-chao Zhang, et al.
The information of location and scattering intensity of the target can be detected by lidar system. The physical characteristics of the target can be retrieved from the scattering intensity. Since the corresponding relationship between the echo signal intensity and the detection range requires to be measured accurately, a weak signal detection system of lidar is needed, with strong electromagnetic immunity, high sensitivity and wide dynamic range. In this paper, firstly, various characteristics of echo signals obtained by aerosol detection lidar, including the signal intensity and frequency spectrum are analyzed. Secondly, the influencing factors associated with those signal characteristics, such as photoelectric detector response time and the dynamic range, are also described. At last, a signal-to-noise ratio model for lidar is established. The influencing factors of the photomultiplier tube shot noise, dark current noise, and background radiation noise to the final SNR can be assessed. Meanwhile, some effective ways to reduce the interference noise are discussed.
Study on plume produced by laser induced of stannum
Qingju Huang, Honghua Wang, Yunlong Huang, et al.
In order to study the radiation properties of plasma plume induced by the interactions between laser and material, the radiation model of plasma plume is established. The properties of plasma plume induced by ultraviolet plused laser induced stannum in neon are thoroughly studied. The pulse width of XeCl ultraviolet laser adopted in the experiment is 10ns, the pulse energy is 90mJ, and the emitted laser wavelength is 308nm. The pressure of neon ambient gas is tunable between 13Pa and 101.3kPa in the induced chamber. Some color photographs of laser-induced plasma plume are obtained through swift and synchronous photograph. The experimental results show that the plasma plume induced by ultraviolet plused laser induced stannum has different color properties at different areas. Under the low pressure of 13Pa, the central area of plasma plume is white; the medial area is mixed color while the outermost area is blue. Each area of the plasma plume decreases gradually as the gas pressure increases, and the color becomes lighter as the atmospheric pressure increases. The main excition mechanisms of light-emission of plasma plume induced by ultraviolet plused laser induced stannumat at different areas are analyzed, and it is believed that there are different light-emission model at different areas. The excition mechanism of the central area of plasma plume is bremsstrahlung, as for medial area and outlying region, it is the combination excition of electrons and ions. The experimental phenomenon that could be explained by the excition model.
A new kind of underwater photoelectric imaging system
Wei-long Ge, Hong-wei Han, Xiao-hui Zhang, et al.
A new kind of underwater imaging system is introduced, called double-channel imaging system, to both improve the detection distance and solve the problem of inherent delay. A image processing subsystem built on TMS320DM642 DSP is in charge of the two channel videos. And software algorithm is used to degrade the noise and improve the contrast of the videos before they are displayed on the monitor. The trails show that images can be acquired at long distance and very close distance. The quality of the images are greatly improved through the image processing subsystem.
Monitoring the effects of photostability in the back-geometry degenerate four wave mixing
Ping-hui Jiang, Wei-bo Wang
The effects of photostability on the ration of signal to noise in degenerate four-wave mixing (DFWM) using backward geometry have been first investigated in iodine vapor. Frequency-doubled outputs from a multi-mode Nd:YAG laser pumped dye laser, which laser dye PM580 was dissolved in the ethanol. Though phase-match is automatically achieved in the backward folded boxcars geometry, weak signal beams under the strong background of stray light are hardly detected because of the photostability on the ratio of signal to noise in DFWM experiments. To solve the problems, a new image processing system for detecting backward DFWM spectroscopy on iodine vapor is reported. This system is composed of CCD camera, imaging processing card and the related software. With the help of the detecting system, the focal image and the beam image of the pump laser's conjugation beam in backward geometry DFWM experiment have been obtain, in which demonstrated that the backward geometry can't compensate the beam excursion. The DFWM signal is sensitive to disturb of the environment, which leads to the phase conjugation fidelity decreased. The study of photostability on the ratio of signal to noise in DFWM experiment is of importance to trace atom, molecular and radical in combustion diagnosis.
Imaging monitoring techniques applications in the transient gratings detection
Experimental studies of Degenerate four-wave mixing (DFWM) in iodine vapor at atmospheric pressure and 0℃ and 25℃ are reported. The Laser-induced grating (LIG) studies are carried out by generating the thermal grating using a pulsed, narrow bandwidth, dye laser .A new image processing system for detecting forward DFWM spectroscopy on iodine vapor is reported. This system is composed of CCD camera, imaging processing card and the related software. With the help of the detecting system, phase matching can be easily achieved in the optical arrangement by crossing the two pumps and the probe as diagonals linking opposite corners of a rectangular box ,and providing a way to position the PhotoMultiplier Tube (PMT) . Also it is practical to know the effect of the pointing stability on the optical path by monitoring facula changing with the laser beam pointing and disturbs of the environment. Finally the effects of Photostability of dye laser on the ration of signal to noise in DFWM using forward geometries have been investigated in iodine vapor. This system makes it feasible that the potential application of FG-DFWM is used as a diagnostic tool in combustion research and environment monitoring.
Computerized laser wavefront alignment with aberration correction using a speckle-based phase retrieval method
Complete laser wavefront, with phase and intensity, is digitally reconstructed using a speckle-based phase retrieval method. An automated technique for the full characterization of a laser beam focus and the correction for astigmatism due to lens rotational misalignment is presented. The technique is also demonstrated in the corrections for illumination beam tilt and lens defocus in the imaging of the high spatial frequency content in phase objects. The proposed wavefront alignment technique is fast, precise and robust against aberrations.
Study of working principle and thermal balance process of a double longitudinal-mode He-Ne laser
A double longitudinal mode He-Ne laser with frequency stabilization is proposed. Compared with general methods, such as Lamb dip, Zeeman splitting and molecule saturation absorption method, this design has some advantages, such as no piezocrystal or magnetic field, a short frequency-stabilized time, lower cost, and higher frequency stability and reproducibility. The metal wire is uniformly wrapped on the discharge tube of the laser. When the metal wire is heated up, the resonant cavity changes with the temperature field around the discharge tube to make the frequency of the laser to be tuned. The polarizations of the two longitudinal modes from the laser must be orthogonal. The parallelly polarized light and the vertically polarized light compete with each other, i. e., the parallelly polarized light generates a larger output power, while, the vertically polarized light correspondingly generates a smaller one, but an equal value is found at the reference frequencies by automatically adjusting the length of the resonant cavity, due to change of the temperature in the discharge tube. Consequently the frequencies of the laser are stabilized. In my experiment, an intracavity He-Ne laser whose length of the resonant cavity is larger than 50mm and smaller than 300mm is selected for the double longitudinal-mode laser. Influence factors of frequency stability of this laser is only change of the length of the resonant cavity. The laser includes three stages: mode hopping, transition stage, and modes stability from startup to laser stability. When this laser is in modes stability, the waveform of heating metal wire is observed to a pulse whose duty is almost 50%, and thermal balances of the resonant cavity mainly rely on discharge tube.
Mie-Rayleigh-Raman lidar for measurement of atmospheric temperature and aerosol extinction
Lingbing Bu, Xingyou Huang, Nianwen Cao, et al.
A Mie-Rayleigh-Raman lidar contains a 200mJ-532nm laser, a 400mm telescope and three detection channels was constructed in this paper. The three detection channels are Mie channel, Rayleigh channel and Raman channel respectively. For the intensity of the aerosol backscattering in boundary layers, analog PMT is used in the Mie channel, from the signal of the analog PMT aerosol extinction can be obtained. The Rayleigh channel detects the Rayleigh backscattering of the atmospheric molecular, while the Raman channel detects the vibrational Raman signal of N2, which is 607nm in the system. From the Rayleigh and Raman channels above, air density profile and then the temperature profile from 5Km to 55Km can be inverted. Primary measurement results were also presented in this paper, to verify the accuracy of the temperature, comparison was conducted between the lidar measurement and the atmospheric model. The result showed good agreements. Backscattering coefficient of aerosol in the range of 10Km was also presented in the end, which indicated the ability of aerosol monitoring.
Visible imaging Fourier transform spectrometer based on a beam-folding technique
Xuzhu Wang, Robert K. Y. Chan
A low-cost visible to Near-infrared Imaging Fourier Transform Spectrometer (IFTS) using a beam-folding technique instead of the spectral folding technique is presented. The retroreflectors are used to replace the plane mirrors to maintain the optical alignments without the adoption of complex active-alignment measures. Fast-scanning mechanism is adopted to avoid the high-cost precise-position control system. The interferogram images at sequential sampling points, spectral images at different wavenumbers and pixel interferograms and spectra of the multimode fiber ends illuminated by a He- Ne laser and a red LED source respectively, are given. The experimental results show that the IFTS based on the beamfolding technique can achieve a spectral resolution of ~15cm-1 (~0.5nm) when measuring the bright coherent light source (the end of a 600 μm fiber coupled with the He-Ne laser). The resolution is mainly limited by the nonlinearity of the CCD output, the memory size of the PC and the data-transferring speed between the PC and the CCD camera PL-A741. Preliminary results showed that it is suited to the measurement of bright object sources. This restriction is only due to the poor performance of the CCD detector array used in the experiment. A fast-scanning visible-Near infrared IFTS for the objects of low light intensity is feasible when the high-sensitivity CCD camera is adopted.
Output characteristics of LMA Yb3+-doped photonic crystal fiber lasers
Hongxin Su, Zelin Guan, Jiang Sun, et al.
The output characteristics of fiber lasers built with large-mode-area(LMA) Yb3+-doped double-clad PCF are experimentally investigated. The gain fiber used in the experimental setup is a LMA Yb3+-doped double-clad PCF, which contains an Yb3+-doped core of 23μm in diameter and a holy inner clad of 420μm in diameter. In the forwardoutput configuration the maximum output is 3.43W and the slope efficiency is 34.6%. At the same pump power, the maximum output in the backward-output configuration is 3.63W and the slope efficiency is 38%. The spectra show that the fiber lasers in both forward-output and backward-output configurations produce multi-wavelength output in a range from 1067nm to 1076nm and unstable. Single wavelength output at 1067.5 nm with a FWHM of about 0.2nm is demonstrated by using a dual-end-output configuration, and a maximum output of 4.25W with a slope efficiency of 44.1% is obtained.
A BP neural network model for sea state recognition using laser altimeter
Chun-bo Shi, Xiao-dong Jia, Sheng Li, et al.
A BP neural network method for the recognition of sea state in laser altimeter is presented in this paper. Sea wave is the typical stochastic disturbance factor of laser altimeter effecting on low-altitude defense penetration of the intelligent antiship missiles, the recognition of sea state is studied in order to satisfy the practical needs of flying over the ocean. The BP neural network fed with the feature vector of laser range-measurement presents the analysis of features and outputs the estimation result of sea state. The two most distinguishing features are the mean and the variance of the sea echo, which are extracted from the distance characteristics of sea echo using general theory of statistics. The use of a feedforward network trained with the back-propagation algorithm is also investigated. The BP neural network is trained using sample data set to the neural network, and then the BP neural network trained is tested to recognize the sea state waiting for the classification. The network output shows the recognition accuracy of the model can up to 88%, and the results of tests show that the BP neural network model for the recognition of sea state is feasible and effective.
A widely tunable QCW Ti:sapphire laser and its frequency doubling with LBO crystal
Ping-xue Li, Gang Li, Meng Chen, et al.
We report an all-solid-state QCW (quasi-continuous-wave) tunable Ti:sapphire laser system from 697nm to 942nm, which was pumped by an intra-cavity frequency doubling Nd:YAG laser at 532nm. Under the pump power of 18W at 532nm with the repetition rate of 3.9kHz, the average output power of 3.5W at 795nm with an optical conversion efficiency of 20% was yielded. Through extra-cavity frequency doubling with the nonlinear crystal LBO (LiB3OWe report an all-solid-state QCW (quasi-continuous-wave) tunable Ti:sapphire laser system from 697nm to 942nm, which was pumped by an intra-cavity frequency doubling Nd:YAG laser at 532nm. Under the pump power of 18W at 532nm with the repetition rate of 3.9kHz, the average output power of 3.5W at 795nm with an optical conversion efficiency of 20% was yielded. Through extra-cavity frequency doubling with the nonlinear crystal LBO (LiB3O5), cut for critical type I phase matching =90°, φ=33.2°) at room temperature, tunable second-harmonic generation (SHG) from 350nm to 465nm was achieved. Through the design of the scan and control system, the whole laser system can be used to expose the sensitive material under the controlling of computer.
Optical system of nano-level vibration measurement by laser Doppler
Li-yan Li, Hua-lin Zeng, Yan Zhou
Through the studying on the M-Z interferometer optical system, the authors give a strict contrast analysis of influence on the steadiness of optical system about optical power, polarization state of laser and optical feedback caused by different types of beam splitters was made. After adjusting and optimizing the optical system, the authors built a high a precision vibration measurement of optical system. The system is advantage at the nano-level vibration measurement, low energy loss and far measuring distance.
The design for the laser detection and warning optical system
Dongmei Li, Guangliang Xiong
Here we present a new optical system for the demands of laser detection and warning optical system which has a large field-of-view (FOV). A staring imaging laser detecting and warning system is formed by using 2-channel uncooled infrared focal plane detectors. In this system, the operating wavelength range is 3~5 microns, and full angle of view is up to 60 degrees. The largest aperture is 30mm and the photosensitive surface diameter of PIN photoelectric detector is line array dimension nearly 12mm. And there are also composed of narrow band filters and signal processing system. A all reflective structure with three elements is used in the object lens to enlarge FOV and back working range, in the head of which the negative mirror have the effect of balancing aberration and deviating rays like a prism. And a standard hyperhemisphere immersion lens with high refractive index is put behind the object lens to satisfy the receiving of a detector with smaller photosensitive surface. The analyzed results show that the image height is 60mm. It redounds to reduce the power of laser and enhances the distance detected.
980-nm Yb-doped single-mode fiber laser and its frequency doubling with BIBO
Shu-zhen Zou, Ping-xue Li
In this paper, a single-mode 980nm Yb-doped fiber laser was studied carefully in theory and experiment. Based on the theoretical research, we chose an appropriate fiber length of 36.5 cm. In the experiment, by adopting two 0° fiber ends as cavity mirrors, the Yb-doped fiber laser generated a total output power of 1.32 W at 980 nm with the slope efficiency of 75.3%.Through frequency doubling with BIBO crystal, a total output power of 15 mW at 490.8 nm was obtained. Simultaneously, we produced a 980nm Yb-doped single-mode pulse fiber laser pumped by an acousto-optics Q-switched Nd:YAG laser. The pulse fiber laser generated a total average power of 100 mW at 980 nm when the laser pulse was 10 ns at repetition frequency of 16 kHz.
Technique of laser in-line ignition all electronic safe and arming device
Ze-rong Guo, Guang-wei Zhou
In modern warfare the performance of weapon system safe and arming device has been put forward higher requirements because the battlefield environment has become increasingly sophisticated. The safe and arming device should have good safety of mechanical, electrical, thermal and other aspects and reliable initiation. This paper analyses the laser initiation of three ways, the laser could initiate the insensitive acceptable charge for the in-line ignition system, so that the laser in-line ignition can be realized and the laser in-line ignition all electronic safe and arming device is built. Then, studies the composition and working principle of the laser in-line ignition all electronic safe and arming device and the various subsystems in-depth. The laser in-line ignition all electronic safe and arming device can be applied to fixed-point, directional and multi-point initiation and has laid an important foundation of the theory and engineering in the future weapon system.
Ultrahigh-resolution full-field optical coherence tomography for imaging of a developing embryo
Bo Wang, Jinggao Zheng, Rui Wang, et al.
Optical coherence tomography (OCT) is a new emerging technique for cross-sectional imaging with high spatial resolution of micrometer scale. It enables in vivo and non-invasive imaging with no need to contact the sample and is widely used in biological and clinic application. In this paper a white-light interference microscope is developed for ultrahigh-resolution full-field optical coherence tomography (Full-Field OCT) to implement 3D imaging of biological tissue. The experimental setup is based on a Linnik-type interferometer illuminated by a tungsten halogen lamp via a bundle of fiber. En-face tomographic images are obtained by demodulation of a combination of interferometric images recorded by a CCD camera. We use a PZT synchronized with the CCD in the reference arm to get the modulated interferometric image and use a programmed precisely controlled electric lift stage in the sample arm to get a 3D image. To fulfill the requirement of in vivo measurement and better match the index of bio-tissue, a pair of high numerical-aperture water immersion microscope objectives is used. Spatial resolution of 1.8μm×1.12μm (transverse×axial) is achieved owing to the extremely short coherence length of the light source and optimized compensation of dispersion mismatch. A shot-noise limited detection sensitivity of 80 dB is obtained at an acquisition time of 5 seconds per image. The development of a mouse embryo is studied layer by layer with our ultrahigh-resolution full-filed OCT. 3D imaging of the embryo can be reconstructed by the OCT images. Information of cell shape, centroid, reflectivity, mitosis period in the development process can be obtained. The variance of the relative reflectivity of an oocyte with time is calculated as well. It is found that the reflectivity of a living oocyte is much lower than that of a dead. Therefore the reflectivity of the cytoplasm can be a signal of the cell activity. In fact, all these parameters above could be very useful for distinguishing the healthy embryos from the morbid, showing high potential for early diagnosis of procreation diseases at cellular level in clinic. More experimental study is still in progress.
Improved WGMAP image restoration
Yan-fei Gao, Yi-he Zhao, Bing-hua Su
Considering that the high-frequency sub-band can gather most energy of noise by the wavelet decomposition, and the local variances in edge and noise change inconsistently, the real edges of images are separated from the noise by choosing an appropriate threshold value in each high-frequency sub-bands of wavelet domain, while the WGMAP method is used to restore the images. Experimental results show that the images reconstructed by the improved algorithm reproduce preferably the edge structures of original images; and the signal to noise ratio and the visual effect are significantly improved.
Absolute absorbing high-power laser energy meter design and precision analysis
Lei Wang, Rongguo Xu, Gaoping Li, et al.
A new kind of absolute absorbing high-power laser energy meter is reported in this paper. The energy meter has the advantage of simpleness, high damage threshold and high precision. The measurement principle, material and the structure of the energy meter is introduced in the paper. Many different kinds of effectors affect the high-power laser energy measurement results, these factors including backscatter, heat loss and accuracy of temperature measurement etc. The paper analyzes all these effectors on the measurement results and the consponding compensating models is given to enhance the measurement results. Energy meter measurement uncertainty is given in the end.
Simulation of underwater objects imaging through rough sea surface based airborne laser range-gated system
Chao Chen, Hong-Ru Yang, Gao-Ping Li, et al.
A model is currently being developed for simulating images of underwater objects as seen by airborne laser range-gated (LRG) system. The simulation model is based on physically accurate models of wind generated waves on the sea surface, and the optical properties of ocean water. It can take as input any digital image and simulate its degradation due to scattering in water and through the wavy sea surface. This paper describes the model implementation for LRG system and presents the results of simulations. Simulation results presented here allow the visual evaluation of image quality for different depth and optical properties of the sea water. These simulations will also allow us to develop optimal strategies for image processing algorithm of Lidar data.
Modeling and simulation of range-gated underwater laser imaging systems
Lei Wu, Yue Shen, Gaoping Li, et al.
There is currently considerable interest in developing electro-optic systems for underwater imaging classification and identification of submerged objects such as fish shoals and mines. The imaging systems can be divided into active imaging systems and passive imaging systems. The main feature of the passive imaging systems is that they haven't illumination sources and depend on lights from targets or surroundings. The active imaging systems use light sources to illuminate the targets and collect the reflection from the targets. The advantages of active imaging systems over passive imaging systems are high contrast and without the affection of environment sources. The gated Intensified CCD (ICCD) cameras are widely used in the active imaging systems because that the laser range-gated (LRG) technology is an effective way to eliminate the backscattering noise. This paper is devoted to present a model for simulation and evaluation the performance of gated ICCD cameras for airborne underwater applications. Some simulation results are presented and discussed.
The principles and design of range-gain-control gated PMT
Yan Li, Hong-ru Yang, Xu-dong Li, et al.
In airborne underwater lidar applications, the reflecting light signal from the sea level is stronger than the one from the underwater object, the returned signal is decreased with the range as exponential and inverse square law and the backscattering return is very large. So the dynamic range could reach five to six orders of magnitude in few hundreds of nanoseconds. Therefore, it is necessary to compress the signal dynamic range to match the range of the digitizing or processing devices, typically 2 or 3 orders of magnitude, and to eliminate the reflecting light signal from the sea level and the backscattering. In this paper, we present a Range-Gain-Control Gated PMT method for this problem. The principal and the design of the Range-Gain-Control Gated PMT system are analyzed and discussed. The experiment results show that this method can complete the gated and the gain-control of the PMT.
High-resolution ladar for multidimension detection: design, modeling, and simulation
Yu-fei Wei, Jin-dong Fei, Qiang Mi, et al.
As the development of application requirements, to obtain more information of the object is an important direction in many research fields. Not only 2-D image, but also range and velocity information are required. Hence, the imaging laser radar technology, which can obtain 3-D or even 4-D information, has been paid more attention. Because of the high range resolution character and direct Doppler frequency shift measurement function, frequency modulation / continuous wave (FM/CW) imaging laser radar can be called a 4-D imaging system. The modulated laser floodlights a moving object, and then the reflecting light is received by optical system and captured by a focal plane array. After obtaining a series of images, the range-Doppler processing algorithm is performed on the pixels with the same position in all the images to calculate the object's range and velocity information, and then a 4-D image (angle - angle - range - velocity) with high accuracy is obtained. This paper describes the FM/CW ladar system's principle, and presents an improved process algorithm to solve the problem of the traditional range-Doppler algorithm's limit used for high velocity object. The simulation results in typical object situation prove that the improved process algorithm could increase the velocity measurement range effectively.
Low-loss antireflection for laser system
Yiqin Ji, Deying Chen, Huasong Liu, et al.
In the laser systems for measurement and so on, like gyro; in its laser cavity or path, it makes use of the optical components which need very high performances, like low loss, low scatter, low reflection, low absorption and high transmittance. In this article, we design and manufacture the 632.8nm(He-Ne laser) low loss AR (LLAR) on crystal quartz, the results show this LLAR have the total loss is about 30ppm and have high uniformity, the fluctuations of the total loss mainly from the surface contamination and the inner defects of crystal material.
Optical orbital angular momentum for optical communication and its measurements
Xi-zheng Ke, Hong Lv, Jing-zhi Wu, et al.
The beam with orbital angular momentum is a present domestic and foreign research key direction. Its application and development will bring the profound influence in the optical communications field. At the same time, light's orbital angular momentum promises potential applications in both classical and quantum optical communication. The research progress of the beam with orbital angular momentum and encoding information as light's OAM for free-space optical communication were reviewed in this article, the existing design method, mechanism and description methods of encoding information as light's OAM were discussed. In quantum communication, qudits can be encoded in photons using their OAM for creating high-dimensional entanglement based on entangled photon pairs from SPDC. In this paper, light's OAM is used as information carrier for classical and quantum communication, which is promising to ensures the security of atmospheric laser communication, improves the density and precision of information transmission. It is apparent that an efficient way to measure the orbital angular momentum of individual photons and light beams with good efficiency would be of potentially great importance for optical communications and quantum information. In view of the above, the measurements of orbital angular momentum of individual photons and light beams are analyzed and discussed in detail.
Methods and apparatus for laser beam scanners with different actuating mechanisms
Si-hai Chen, Si-hua Xiang, Xin Wu, et al.
In this paper, 3 types of laser beam scanner are introduced. One is transmissive beam scanner, which is composed of convex and concave microlens arrays (MLAs). By moving the concave lens in the plane vertical to the optical axis, the incident beam can be deflected in two dimensions. Those two kinds of MLAs are fabricated by thermal reflow and replication process. A set of mechanical scanner frame is fabricated with the two MLAs assembling in it. The testing result shown that the beam deflection angles are 9.5° and 9.6°, in the 2 dimension(2D) with the scanning frequency of 2 HZ and 8 HZ, respectively. The second type of laser beam scanner is actuated by voice coil actuators (VCAs). Based on ANSOFT MAXWELL software, we have designed VCAs with small size and large force which have optimized properties. The model of VCAs is built using AutoCAD and is analyzed by Ansoft maxwell. According to the simulation results, high performance VCAs are fabricated and tested. The result is that the force of the VCAs is 6.39N/A, and the displacement is ±2.5mm. A set up of beam scanner is fabricated and actuated by the designed VCAs. The testing result shown that the two dimensional scanning angle is 15° and 10° respectively at the frequency of 60HZ. The two dimensional scanning angle is 8.3° and 6° respectively at the frequency of 100HZ. The third type of scanner is actuated by amplified piezoelectric actuators (APAs). The scanning mirror is actuated by the piezoelectric (PZ) actuators with the scanning frequency of 700HZ, 250HZ and 87HZ respectively. The optical scanning angle is ±0.5° at the three frequencies.
The application of fractional Fourier transform in the nonlinear optical imaging measurement
Zongjie Zhu, Yuxiao Wang, Xueru Zhang, et al.
The 4f coherent imaging system with phase object (PO) is a new method to measure the third-order nonlinearity. The essential of the measurement is using a diaphragm with phase object to modulate the nonlinear phase shift in the nonlinear sample, which is placed at the Fourier plane of the 4f system, to change of the amplitude of the electric field in the image plane. In this paper Fractional Fourier Transform (FRFT) is applied to the 4f coherent imaging system for the third-order nonlinear refraction measurements. With the help of Fresnel diffraction, we obtain FRFT using the single-lens system, Lohmann type system. The improved measurement system is obtained with FRFT in place of FT after the beam pass through the sample. We numerically analyze the effects of fractional order on the diffraction image of the improved nonlinear measurement system. Comparing with the original 4f system, when the fractional order a is 0.4 the sensitivity which is measured by ΔT (ΔT is proportional to the fluence inside and outside of PO on the image plane) is improved.