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- Front Matter: Volume 8905
- Laser Sensing and Imaging Applications
Front Matter: Volume 8905
Front Matter: Volume 8905
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This PDF file contains the front matter associated with SPIE Proceedings Volume 8905 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Laser Sensing and Imaging Applications
The mutual coherent and incoherent function for laser pulse scattering fields from one-dimensional rough surface
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It has used the two-frequency mutual coherent function to study pulse scattering from one dimensional perfectly conducting rough surface. So this paper is mainly focused on that the analytical expressions for incoherent mutual function（MCF) for pulse scattering from one-dimensional random rough surface are obtained based on the Kirchhoff’s approximation. According to the analytical solutions, numerical methods are shown that coherent and incoherent mutual function（MCF）change with the coherence bandwidth frequency difference and scattering angles in different incident angles incidence on laser（1.06μm）according to the mean of fluctuating heights and correlation length of the rough surfaces. And some important scattering characteristics of the coherent and incoherent mutual function（MCF）are be obtained in details. Our works is helpful when investigating the statistical characteristics of laser scattering fields of objects with rough surface.
A convenient fabrication method of glass helicoid
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In this paper, we present a new and simple method to produce larger height (with millimeter-sized) helical surface
compared with the other methods. During the process, a convenient method for the fabrication of the helical substrate
made of B270 glass by using a smart oven is presented. A Global 7107 Coordinate Measuring Machines (CMM) is used
for the detection of the glass helicoid. The experimental results proved to be in agreement with the theoretical prediction
within the uncertainty of the error and can satisfied our requirement. Moreover, this method seems easy and simple to
produce larger height helical surface compared with other ways mentioned in the literature.
Low stratospheric zero wind layer measurement with Rayleigh Doppler lidar
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Wind field is measured with a mobile Rayleigh Doppler Wind Lidar in China(41°N, 86°E). According to statistic
data of wind field experiment in present-year, the low stratospheric zero wind Layer character over the region in summer
and early autumn has been obtained, the zero wind layer generally exists on the height of from 18km to 23km, the wind
speed is mostly less than 8m/s and the wind direction of zero wind layer understratum and superstratum is inverse.
Research on semiconductor laser frequency stabilization
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Narrow linewidth and high stability of frequency are extremely necessary in modern precision experiments. The frequency of a free running semiconductor laser will drift several GHz per day, far too much to fulfill the demands in atomic and laser physics. In order to overcome this disadvantage, a variety of technologies for frequency stabilization are researched. The experimental realizations of frequency stabilization based on 780nm semiconductor laser are described in detail. Meanwhile, the performance and capabilities of the various frequency stabilization technologies are analyzed.
Laser speckle reduction based on compressive sensing and edge detection
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Polarization active imager technology obtains images encoded by parameters different than just the
reflectivity and therefore provides new information on the image. So polarization active imager systems represent a very
powerful observation tool. However, automatic interpretation of the information contained in the reflected intensity of the
polarization active image data is extremely difficult because of the speckle phenomenon. An approach for speckle
reduction of polarization active image based on the concepts of compressive sensing (CS) theory and edge detection.
First, A Canny operator is first utilized to detect and remove edges from the polarization active image. Then, a dictionary
learning algorithm which is applied to sparse image representation. The dictionary learning problem is expressed as a
box-constrained quadratic program and a fast projected gradient method is introduced to solve it. The Gradient
Projection for Square Reconstruction (GPSR) algorithm for solving bound constrained quadratic programming to reduce
the speckle noise in the polarization active images. The block-matching 3-D (BM3D) algorithm is used to reduce speckle
nosie, it works in two steps: The first one uses hard thresholding to build a relatively clean image for estimating statistics,
while the second one performs the actual denoising through empirical Wiener filtering in the transform domain. Finally,
the removed edges are added to the reconstructed image. Experimental results show that the visual quality and evaluation
indexes outperform the other methods with no edge preservation. The proposed algorithm effectively realizes both
despeckling and edge preservation and reaches the state-of-the-art performance.
Research on ESPI image enhancement technology
Di Wu,
Lei Dai,
Chang-song Yu
Show abstract
Electronic Speckle Pattern Interferometry (ESPI) technology is used for non-contact measurement. However,
original ESPI images are with fluent speckle noise, which leads to low ratio of signal-to-noise. Both reducing the
speckle noise and preserve the fringe pattern are important in EPSI image enhancement. Nowadays the partial
differential equation method is widely used for EPSI image enhancement. It has advantages that can reduce speckle
noise and protect the edge of fringe pattern. By discussing the factors of this method, comparing the enhancement
results, we try to give out conclusion that the best choice for EPSI image enhancement applications.
The simulation of adaptive optical image even and pulse noise and research of image quality evaluation
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As optical image becomes more and more important in adaptive optics area, and adaptive optical telescopes play a more and more important role in the detection system on the ground, and the images we get are so many that we need find a suitable method to choose good quality images automatically in order to save human power, people pay more and more attention in image’s evaluation methods and their characteristics. According to different image degradation model, the applicability of different image’s quality evaluation method will be different. Researchers have paid most attention in how to improve or build new method to evaluate degraded images. Now we should change our way to take some research in the models of degradation of images, the reasons of image degradation, and the relations among different degraded images and different image quality evaluation methods. In this paper, we build models of even noise and pulse noise based on their definition and get degraded images using these models, and we take research in six kinds of usual image quality evaluation methods such as square error method, sum of multi-power of grey scale method, entropy method, Fisher function method, Sobel method, and sum of grads method, and we make computer software for these methods to use easily to evaluate all kinds of images input. Then we evaluate the images’ qualities with different evaluation methods and analyze the results of six kinds of methods, and finally we get many important results. Such as the characteristics of every method for evaluating qualities of degraded images of even noise, the characteristics of every method for evaluating qualities of degraded images of pulse noise, and the best method to evaluate images which affected by tow kinds of noise both and the characteristics of this method. These results are important to image’s choosing automatically, and this will help we to manage the images we get through adaptive optical telescopes base on the ground.
Comb-like supercontinuum generated by dual-pulse filamentation in air
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Comb-like supercontinuum generation is investigated with dual-pulse filamentation in air. The period of spectral
fringes varies with the time delay between collinearly propagating pulses. The comb-like supercontinuum may be a
potential tool for optical remote sensing.
Multi-pulse detection performance analysis for spaceborne laser radar based on single-photon
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As an active detection method, the positioning performance and vertical accuracy of spaceborne laser radar are superior to inactive method. On account of the energy constrain on space, the laser radar operation mode need to be researched for imaging in high probability. In this paper, the influence of system detection probability resulted from the multi-pulse emission mode under the same total power is studied, and provided the detection probability equation in both cases as noise signal and no-noise signal. With the principle of mean squared error, this paper researched the multi-pulse detection error. Finally, above conclusions are simulated in numerical method. The results indicate that the detection advantage in multi-pulse mode become more remarkable with the increasing noise signal.
The tip/tilt tracking sensor based on multi-anode photo-multiplier tube
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Based on the demands of high sensitivity, precision and frame rate of tip/tilt tracking sensors in acquisition, tracking and pointing (ATP) systems for satellite-ground optical communications, this paper proposes to employ the multiple-anode photo-multiplier tubes (MAPMTs) in tip/tilt tracking sensors. Meanwhile, an array-type photon-counting system was designed to meet the requirements of the tip/tilt tracking sensors. The experiment results show that the tip/tilt tracking sensors based on MAPMTs can achieve photon sensitivity and high frame rate as well as low noise.
The design of charge-sensitive preamplifier with differential JFET input
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In the highly sensitive detection field, charge-sensitive amplifier is widely used in the preamplifier of detectors, however, the high voltage applied to these detectors (such as CZT nuclear detector) often make serious noise, which may influence the sensitivity of the detector. Despite the traditional passive filter circuit to eliminate the noise of the power, but if the power supply accuracy isn’t high enough and the passive circuit eliminate the power supply noise is incomplete. The noise still may affect the performance of the final system. According to the need of nuclear detection and photoelectric detection, a kind of differential JFET charge-sensitive preamplifier is proposed in this paper, which eliminates the power-supply noise and Johnson noise of bias resistance. First, theoretical analysis of the traditional JFET circuit is proved and simulation of the JFET circuit is performed with ORCAD software, which prove that power-supply noise effect the preamplifier. Next, simulation of the innovative circuit is performed with ORCAD software. Finally, the fabricated circuit board is tested with avalanche photo diode (APD). It is shown that the charge-sensitive preamplifier with differential JFET input can significantly eliminate the power-supply noise and Johnson noise of resistance (both low frequency and high frequency) and realize a high sensitivity.
Simulation of laser beam propagation through the troposphere
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Understanding and predicting laser beam propagation effects in the atmosphere is important for laser applications. Turbulence effects cause beam wander, beam broadening, intensity scintillations, which reducing the power in bucket and the tracking accuracy, etc. In this work, the phase screens are used to model atmosphere turbulence in the model of the laser propagation through troposphere. And according to the characteristics of the troposphere，a layered model is used. Laser propagation follows the Huygens-Fresnel principle between phase screens. Simulations with different grid point numbers were constructed, and numerical experiments were conducted. According to the simulated results including Strehl ratio, sharpness, and amplitude distribution, preceding phase screens have effect on the total energy of the receiving surface, but have little impact on amplitude distribution. And the phase screens, which are close to the receiving surface, have a significant impact on both amplitude distribution and the total receiving energy. The results suggests that in simulation one should increase grid point numbers as many as possible and needs to pay particular attention to parameters of the phase screens near the receiving surface in simulation.
850nm vertical cavity surface emitting lasers utilizing the self-planar mesa structure
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We presented the self-planar mesa structure for improving the performances of 850-nm oxide-confined vertical cavity
surface emitting lasers (VCSELs). Thermal simulation results demonstrated that the enhanced lateral heat dissipation and
decreased series resistance within VCSELs could be gained using the self-planar mesa structure. By employing the selfplanar
mesa, the maximum output power was increased from 8mW to more than 11mW, and the maximum wall-plug
efficiency was improved from 26% to 36% for the VCSEL with an oxide aperture size of 13 μm at 15°C.
Multi-channel automotive night vision system
Gang Lu,
Li-jun Wang,
Yi Zhang
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A four-channel automotive night vision system is designed and developed .It is consist of the four active near-infrared
cameras and an Mulit-channel image processing display unit,cameras were placed in the automobile front, left, right and
rear of the system .The system uses near-infrared laser light source，the laser light beam is collimated, the light source
contains a thermoelectric cooler (TEC),It can be synchronized with the camera focusing, also has an automatic light
intensity adjustment, and thus can ensure the image quality.
The principle of composition of the system is description in detail,on this basis, beam collimation,the LD driving and LD
temperature control of near-infrared laser light source,four-channel image processing display are discussed.The system
can be used in driver assistance, car BLIS, car parking assist system and car alarm system in day and night.
Study of hollow cone laser and its application
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In the early nineteenth century, People paid attention to the phenomenon that the biaxial crystal could produce conical
refraction. A bunch of solid quasi-monochromatic beam can be considered as the light source, when the laser propagates
through the biaxial crystal, the "funnel-shaped" hollow cone laser can generate inside the biaxial crystal or outside. This
paper is based on this point to study the hollow cone laser that produced by biaxial crystal.
In this paper, the ring size of the conical refraction can change with incident angle from refractive indices ellipsoid of
biaxial crystal. Through computer simulation, the characteristics biaxial crystal produce conical refraction can be
analyzed. When laser propagate through the biaxial crystal, the phenomenon of absorption and dispersion is appeared,
and it will affect on the transmission quality.
According to the absorption and dispersion properties of conical refraction, the spatial coherence decrease when laser
propagates through the biaxial crystal. The beam propagation direction will change with refractive index, which will
cause the change of optical path length. In addition, the experiments and theoretical study can achieve the same results.
This paper also discuses the hollow cone laser can be applied to optical switching, radar scanner, copier, scanner and
other applications.
The temperature measurement research for high-speed flow based on tunable diode laser absorption spectroscopy
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Due to the particularity of the high-speed flow, in order to accurately obtain its’ temperature, the measurement system
should has some characteristics of not interfereing with the flow, non-contact measurement and high time resolution. The
traditional measurement method cannot meet the above requirements, however the measurement method based on
tunable diode laser absorption spectroscopy (TDLAS) technology can meet the requirements for high-speed flow
temperature measurement. When the near-infared light of a specific frequency is through the media to be measured, it
will be absorbed by the water vapor molecules and then the transmission light intensity is detected by the detector. The
temperature of the water vapor which is also the high-speed flow temperature, can be accurately obtained by the
Beer-Lambert law. This paper focused on the research of absorption spectrum method for high speed flow temperature
measurement with the scope of 250K-500K. Firstly, spectral line selection method for low temperature measurement of
high-speed flow is discussed. Selected absorption lines should be isolated and have a high peak absorption within the
range of 250-500K, at the same time the interference of the other lines should be avoided, so that a high measurement
accuracy can be obtained. According to the near-infrared absorption spectra characteristics of water vapor, four
absorption lines at the near 1395 nm and 1409 nm are selected. Secondly, a system for the temperature measurement of
the water vapor in the high-speed flow is established. Room temperature are measured through two methods, direct
absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) ,the results show that this system can
realize on-line measurement of the temperature and the measurement error is about 3%. Finally, the system will be used
for temperature measurement of the high-speed flow in the shock tunnel, its feasibility of measurement is analyzed.
Intensity information extraction in Geiger mode detector array based three-dimensional imaging applications
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Geiger-mode detectors have single photon sensitivity and picoseconds timing resolution, which make it a good candidate for low light level ranging applications, especially in the case of flash three dimensional imaging applications where the received laser power is extremely limited. Another advantage of Geiger-mode APD is their capability of large output current which can drive CMOS timing circuit directly, which means that larger format focal plane arrays can be easily fabricated using the mature CMOS technology. However Geiger-mode detector based FPAs can only measure the range information of a scene but not the reflectivity. Reflectivity is a major characteristic which can help target classification and identification. According to Poisson statistic nature, detection probability is tightly connected to the incident number of photon. Employing this relation, a signal intensity estimation method based on probability inversion is proposed. Instead of measuring intensity directly, several detections are conducted, then the detection probability is obtained and the intensity is estimated using this method. The relation between the estimator’s accuracy, measuring range and number of detections are discussed based on statistical theory. Finally Monte-Carlo simulation is conducted to verify the correctness of this theory. Using 100 times of detection, signal intensity equal to 4.6 photons per detection can be measured using this method. With slight modification of measuring strategy, intensity information can be obtained using current Geiger-mode detector based FPAs, which can enrich the information acquired and broaden the application field of current technology.
A novel design measuring method based on linearly polarized laser interference
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The interferometric method is widely used in the precision measurement, including the surface quality of the large-aperture mirror. The laser interference technology has been developing rapidly as the laser sources become more and more mature and reliable. We adopted the laser diode as the source for the sake of the short coherent wavelength of it for the optical path difference of the system is quite shorter as several wavelengths, and the power of laser diode is sufficient for measurement and safe to human eye. The 673nm linearly laser was selected and we construct a novel form of interferometric system as we called ‘Closed Loop’, comprised of polarizing optical components, such as polarizing prism and quartz wave plate, the light from the source split by which into measuring beam and referencing beam, they’ve both reflected by the measuring mirror, after the two beams transforming into circular polarization and spinning in the opposite directions we induced the polarized light synchronous phase shift interference technology to get the detecting fringes, which transfers the phase shifting in time domain to space, so that we did not need to consider the precise-controlled shift of optical path difference, which will introduce the disturbance of the air current and vibration. We got the interference fringes from four different CCD cameras well-alignment, and the fringes are shifted into four different phases of 0, π/2, π, and 3π/2 in time. After obtaining the images from the CCD cameras, we need to align the interference fringes pixel to pixel from different CCD cameras, and synthesis the rough morphology, after getting rid of systematic error, we could calculate the surface accuracy of the measuring mirror. This novel design detecting method could be applied into measuring the optical system aberration, and it would develop into the setup of the portable structural interferometer and widely used in different measuring circumstances.
Analysis on the influences of range-gated underwater laser imaging system parameters on the signal to noise ratio
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Range-gated underwater laser imaging system is a kind of underwater photoelectric imaging system which is based on the principle of time label for target. Through controlling the imaging time of photoelectric equipment precisely, it can effectively restrain the backscatter of water, having longer detective distance than generic ones. A range-gated underwater laser imaging system consists of pulse laser illumination system, photoelectric imaging system (ICCD) and control system commonly. When the moment and the time of ICCD opening gate are given, the lights that could be received by ICCD include the backscatter of water, the direct component and forward scatter of reflected light of the target in the imaging processing of range-gated underwater laser imaging system. Computing model of light energy received by ICCD was built in this paper. The direct component and forward scatter of reflected light energy were analyzed and the calculation methods based on PSF theory were studied. The backscatter light energy of water was calculated through water layering. The signal to noise ratio of range-gated underwater laser imaging system was defined. The impact of target range, target reflection ratio, ICCD gating width and water attenuation coefficient on the signal to noise ratio were analyzed and simulation results were given.
A novel switchable triple-wavelength Er3+-doped fiber laser based on AWG and FBGs
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A simple and effective switchable triple-wavelength Er3+-doped fiber laser with narrow-line-width oscillating output is proposed and demonstrated. Only using an arrayed-waveguide grating (AWG) as the comber filter and FBGs as narrow band reflectors of each F-P cavity, a stable simultaneous triple-wavelength oscillation is achieved at room temperature. The output can be switched between single- and triple-wavelength by controlling the LD pump respectively. The side mode suppression ratio and the 3-dB bandwidth of the laser’s outputs are measured to be more than 55dB and less than 10pm. Moreover, the output power stability of the laser has also been measured and analyzed.
The mathematical model reduces the effect of distance to the scatter images gray level
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In x-ray scanning system, scatter images are obtained to provide information on material density. The forward and
backward scatter is related to solid angle. Scatter is therefore dependent on the distance of the scanned object from the
x-ray source. In the real world, an object may be placed anywhere on the conveyer belt, so the measured intensity will
contain errors relative to the ideal intensity. This makes classification results less reliable. Extraction of characteristic
values L associated with the density; need to know the gray levels of scatter images, so how to base on forward scatter
and back scatter images to determine the scatter image gray level is first necessary to solve the problem. The author
combined with the forward scatter and backscatter images，then established higher order gray-level mathematical model
of scattering images, to eliminate the impact of distance on the scatter images, to obtain more accurate gray level of
scatter image. Then compare the error use of LMS algorithm and the LS algorithm to solving mathematical model
parameters, LS algorithm ultimately prove less error and experimental validation of the superiority of the LS algorithm.
Research on range-gated laser active imaging seeker
Mu You,
PengHui Wang,
DongJie Tan
Show abstract
Compared with other imaging methods such as millimeter wave imaging, infrared imaging and visible light imaging, laser imaging provides both a 2-D array of reflected intensity data as well as 2-D array of range data, which is the most important data for use in autonomous target acquisition .In terms of application, it can be widely used in military fields such as radar, guidance and fuse. In this paper, we present a laser active imaging seeker system based on range-gated laser transmitter and sensor technology .The seeker system presented here consist of two important part, one is laser image system, which uses a negative lens to diverge the light from a pulse laser to flood illuminate a target, return light is collected by a camera lens, each laser pulse triggers the camera delay and shutter. The other is stabilization gimbals, which is designed to be a rotatable structure both in azimuth and elevation angles. The laser image system consists of transmitter and receiver. The transmitter is based on diode pumped solid-state lasers that are passively Q-switched at 532nm wavelength. A visible wavelength was chosen because the receiver uses a Gen III image intensifier tube with a spectral sensitivity limited to wavelengths less than 900nm.The receiver is image intensifier tube’s micro channel plate coupled into high sensitivity charge coupled device camera. The image has been taken at range over one kilometer and can be taken at much longer range in better weather. Image frame frequency can be changed according to requirement of guidance with modifiable range gate, The instantaneous field of views of the system was found to be 2×2 deg. Since completion of system integration, the seeker system has gone through a series of tests both in the lab and in the outdoor field. Two different kinds of buildings have been chosen as target, which is located at range from 200m up to 1000m.To simulate dynamic process of range change between missile and target, the seeker system has been placed on the truck vehicle running along the road in an expected speed. The test result shows qualified image and good performance of the seeker system.
The helicopter flight test analysis of all-fiber laser Doppler velocity sensor
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This paper gives a novel All-Fiber laser Doppler Velocity Sensor(ALDVS) to measure the relative velocity to the lunar
or planetary bodies during the vehicle landing phase. In the beginning of the paper, A brief description of the principle of
laser Doppler velocity sensor is given. After that, the paper gives the laser Doppler velocity sensor configuration. The
paper introduce the helicopter flight test that was held in Zhengzhou. The altitude of flight is about 3km.The laser
Doppler velocity data is analysed. The GPS velocity data and laser Doppler velocity sensor velocity information are
compared. Finally, the equivalent distant in moon is calculated and the measurement error is discussed.
The research of multi-frame target recognition based on laser active imaging
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Laser active imaging is fit to conditions such as no difference in temperature between target and background, pitch-black night, bad visibility. Also it can be used to detect a faint target in long range or small target in deep space, which has advantage of high definition and good contrast. In one word, it is immune to environment. However, due to the affect of long distance, limited laser energy and atmospheric backscatter, it is impossible to illuminate the whole scene at the same time. It means that the target in every single frame is unevenly or partly illuminated, which make the recognition more difficult. At the same time the speckle noise which is common in laser active imaging blurs the images . In this paper we do some research on laser active imaging and propose a new target recognition method based on multi-frame images . Firstly, multi pulses of laser is used to obtain sub-images for different parts of scene. A denoising method combined homomorphic filter with wavelet domain SURE is used to suppress speckle noise. And blind deconvolution is introduced to obtain low-noise and clear sub-images. Then these sub-images are registered and stitched to combine a completely and uniformly illuminated scene image. After that, a new target recognition method based on contour moments is proposed. Firstly, canny operator is used to obtain contours. For each contour, seven invariant Hu moments are calculated to generate the feature vectors. At last the feature vectors are input into double hidden layers BP neural network for classification . Experiments results indicate that the proposed algorithm could achieve a high recognition rate and satisfactory real-time performance for laser active imaging.
Research of boron films deposited on different substrates
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Semiconductor detector that incorporate neutron reactive material within the same detector demonstrates a new method for neutron dosimetry and boron neutron reactive therapy seems to be a promising treatment. Boron films were deposited on single crystalline silicon, glass, and CVD diamond film by magnetron sputtering, close-space sublimation and vacuum evaporation. The properties of the samples were characterized by SEM, which shows vacuum evaporation method is suitable for depositing high quality boron films.
Design of information field command values emulation system
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An information field command values emulation system was designed to meet the requirements of testing and emending the information field testing devices. According to form principle of information field command values, the FPGA (Field-Programmable Gate Array) was used to design the emulation system of information field command values, drive the laser to produce simulate information field command values. By comparing the simulate values and the theoretic values, it can be educed that the precision of the simulate values is high enough to verified the feasibility of the emulation system, therefore it can be concluded that the emulation system can meet the corresponding requirements.
The applications of laser tracking and ranging technology in space rendezvous and docking
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With the development of space technology, more and more Rendezvous and Docking (RVD) mission require more precise measurement of relative position and attitude between tracking spacecraft and target spacecraft. In the procedure of docking between near spacecraft , the optical retroreflector on the target Spacecraft were tracked by the laser tracking and ranging device on the tracking spacecraft , the distance data were provided by laser ranging system, and the azimuth data were provided by tracking gimbal, Synthesized the distance data and azimuth data, the relative position information between two spacecraft were provided to the target spacecraft. Furthermore, through tracking more than three point on the target spacecraft ,the complete information of relative position and attitude between two spacecraft were calculated rapidly by the measurement system，which were presented to the control system during the whole RVD operating stage. The laser tracking technology guaranteed continuous measurement and supplied accurate azimuth information, and the laser ranging technology ensured high accuracy of distance information. In addition, the untouched measure mode give no disturbance to the docking operation, moreover, the monochromaticity of laser make the tracking and ranging procedure avoiding to be disturbed by parasitic light of space, thus there will be a effective measurement accompanying the whole docking operating procedure and affording valid data to the control system of docking.
A novel optical scanner for laser radar
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Laser radar are ideally suitable for recognizing objects, detection, target tracking or obstacle avoidance, because of the high angular and range resolution. In recent years, scannerless ladar has developed rapidly. In contrast with traditional scanner ladar, scannerless ladar has distinct characteristics such as small, compact, high frame rate, wide field of view and high reliability. However, the scannerless ladar is still in the stage of laboratory and the performance cannot meet the demands of practical applications. Hence, traditional scanner laser radar is still mainly applied. In scanner ladar system, optical scanner is the key component which can deflect the direction of laser beam to the target. We investigated a novel scanner based on the characteristic of fiber’s light-conductive. The fiber bundles are arranged in a special structure which connected to a motor. When motor working properly, the laser passes through the fibers on incident plane and the location of laser spot on output plane will move along with a straight line in a constant speed. The direction of light will be deflected by taking advantage of transmitting optics, then the linear sweeping of the target can be achieved. A laser radar scheme with high speed and large field of view can be realized. Some researches on scanner are simply introduced on section1. The structure of the optical scanner will be described and the practical applications of the scanner in transmitting and receiving optical paths are discussed in section2. Some characteristic of scanner is calculated in section3. In section4, we report the simulation and experiment of our prototype.
Quadratic phase error compensation algorithm based on phase cancellation for ISAIL
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As a product combining inverse synthetic aperture technology with coherent laser technology, Inverse Synthetic Aperture
Imaging Ladar (ISAIL) overcomes the diffraction limit of the telescope’s aperture, while it supplies a much better range
resolution which will not get worse at long range when the diameter telescope optics becomes smaller. Compared with
traditional microwave imaging radar, SAIL can provide a much higher-resolution image because of shorter wavelength,
and its shorter imaging time for coherent integration takes a great part in practical application. The rotational motion of
target generates Migration through Range Cells (MTRC) because of the ultra-high resolution of ISAIL. Quadratic Phase
Error (QPE) caused by Migration through Range Cells (MTRC) during the imaging time makes ISAIL image smeared. It
is difficult to estimate the QPE through traditional motion compensation algorithm. To solve this problem in the case of
uniform rotation rate, a novel QPE compensation method, based on Phase Cancellation (PC), is proposed. Firstly, a
rough range of QPE coefficient related to the wave-length, length of the target, and the rotating angle is estimated. Then,
through 1-D search, the QPE coefficient is obtained exactly. Finally, the QPE compensation is achieved. The ISAIL
imaging experiments with numerical data validate the feasibility and effectiveness of the proposed algorithm.
Research on polarization state of prism coupler sensor for measuring liquid refractive index
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Due to many experimental data required and a lot of calculations involved, it is very complex and cumbersome to model prism-based liquid-refractive-index-measuring methods. By use of the feature of TE-polarized wave and TM-polarized wave and differential measurement principle, we developed a new method of mathematical modeling for measuring refractive index of a liquid based upon Fresnel formula and prism internal reflection at incident angle less than critical angle. With this method only two different concentrations measurements for a kind of solution can lead to the determination of computational model. It introduces the principle of an optic-fiber sensor system based on prism-coupler for measuring refractive index of a liquid, and it contains the configuration picture of the sensing optical path, the spectrogram of the semiconductor laser and the structure block diagram of measuring system, the system is mainly made up of the semiconductor laser with 1654.14nm in wavelength, 1×2 optical switch, Y-shaped photo-coupler with coupled rate 50:50, the detector based on isosceles prism-coupler, the data process and control system based on AT89C51 and photoelectric transformer. For TM-polarized wave and TE-polarized wave, theoretical simulations show that the ratio of sensitivity is 1.11, therefore, the beam that the component of TM-polarized wave is more than the one of TE-polarized wave is advantageous to heightening the systemۥs measurement sensitivity. Measurements are performed to examine the validity of the theoretical model and four theoretical models are given, and these results indicate the feasibility of four theoretical models with an error of 3%. In this study, a beam of light is broken down into two beams in the coupler of Y-shaped coupler, the one acts as the reference optical path, the other is known as the sensing optical path, consequently the method can limit well the fluctuation of the light source, the variation of the photodiodeۥ s dark-current of photodiode and many other interfering factors and can be used for real-time detection and online analysis of liquid refractive-index. The method is also capable of measuring even smaller changes in the optical refractive index of the material on a metal surface by the surface plasma resonance sensing techniques.
Target detection technology based on polarization imaging in the complex environment
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The polarization imaging detection technology has some advantages in revealling targets in complex background, identify stealthy, camouflage, dim, false target, and "penetrating smoke". This article summarizes foreign polarization imaging detection technology development process, the status
and development trends, and discusses the foreign technical level, further research on key technology of polarization imaging detection, put forward a scheme of the detection system based on polarization imaging in complex environment, through increasing the polarization dimension information based on
intensity imaging , on which intensity and spectrum cannot reflect, and can significantly enhance the
difference between target and background, increase influencing distance in the haze, smoke and dust
environment , through the analysis, we elucidated the feasibility and availability of the system, in order
to enhance the future of the target detection and recognition ability of photoelectric equipment.
The micro-cavity lasers with different device sizes for the directional emission
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Micro-cavity lasers have attracted more and more attention due to their low threshold, high cavity Q factor and
being suitable for high density optoelectronic integration. However, the optical power output is very low due to
total internal reflection of the whispering gallery modes WGMs, and their far-field profiles are isotropic due to
isotropic micro-cavity structures. In this paper, we presented the limason-shaped cavity devices with different sizes
for directional emission, and investigated their output characteristics in experiments. In experiment, mid-infrared
quantum cascade lasers material was used to fabricate the micro-cavity lasers for its advantages for the micro-disk
geometry due to their lack of surface recombination and inherently in-plane, transverse magnetic (TM) mode
emission. By employing InP based InGaAs/InAlAs quantum cascade lasers material, the micro-cavity lasers are
presented and investigated the output emission characteristics such as light output power, threshold current, and
cavity quality Q factor.
Application of simple adaptive control to rate gyroscope stable platform system
Show abstract
For a class of nonlinear systems with dynamic uncertainties, adaptive stabilization problem is considered in the rate gyroscope of stable platform system. Since the uncertainties are inevitable in the practical model of systems, the robust property of the systems in the presence of parametric uncertainties is important to be considered, such as modeling error, external disturbances, etc. Due to the strong nonlinearity and coupling characteristic of systems, it is difficult to obtain the precise model, and the nonlinearity cannot be cancelled exactly so that the controller performs badly. Adaptive control (AC) can adapt to parameter variations, but it is not applicable to the transition phase. A way to optimize the overall disturbances rejection performance of the AC system in the presence of unknown external disturbances existing in the stable platform system is provided in this paper. According to the construction of stable platform system based on gyroscope stabilized platform, the coordinate systems related to stable platform system are defined, and its mathematical model of stabilized platform is build up. Using the SIMULINK of MATLAB, the model is applied to the computer simulation of the stable platform system with good results. The author designed the control law of velocity-loop respective with the method of continuous correcting net and the AC. The simulation results show that the designed adaptive control law can satisfy the required criterion, it proves that the design method is feasible. In order to compare the above two method efficiently, the author gives the seeker system step response, square wave response especially. Adaptive control law is confirmed to give better tracking performance compared with correcting net control, and a control precision comparable to seeker system and higher robustness to parameter change, despite the simple controller. The research results ensure a wider application of simple AC in real mechanical systems.
Study on two-dimensional tomography algorithm for gas temperature distribution based on TDLAS
Show abstract
In the combustion flow field, the concentrations of temperature and water vapor are very important in
determining combustion efficiency. The traditional contact measurement will induce shock so as to disturb the flow field, and most of the probe can’t be used in the high temperature air. So the existing contact measurement
method can't meet the measurement requirements of the combustion field, but the tunable laser absorption
spectrum technology (TDLAS) can realize non-contact nondestructive measurement of the combustion flow field. Various parameters such as temperature, gas composition and concentration, flow velocity, can be measured at the same time. And there is no temperature limit. It is very good at measuring combustion field parameters in the high
temperature and high speed environment. TDLAS can calculate the gas temperature in real-time by scanning both absorption signal of gas absorption lines, but this is one-dimensional path integral measurement, can’t reflect the real information of the combustion
field. So it can't be used to measure objects with distinct temperature gradient. In order to overcome this
deficiency, tunable laser absorption spectrum technology combined with computer tomography technology (called TDLAT) is used to realize the measurement of the two dimensional temperature distribution in the burning flow field. In this paper, the measurement principle and algorithm of the two dimensional temperature field distribution are put forward. In TDLAT system, the measured area is divided into many grids. TDLAS is used to get the laser
path integral spectrophotometry along the grid line. In succession, deeply grid information is gotten by non-negative constrained least squares. Thus, assuming that temperature measurement plane within is in smooth
transition, interpolation algorithm is used to recreate the high spatial resolution of the two dimensional
temperature field distribution. According to the measuring principle and measuring objects, the model established
is used to get the simulation result. The algorithm for TDLAT system was also verified to determine where it is consistent or not. As a result, the deviation value is less than 3% between the result of the temperature distribution
and original hypothesis spectrophotometry, which shows that the algorithm is self-consistent.
Exploration of noninvasive determination of blood glucose concentration by using photoacoustic technique
Show abstract
Photoacoustic (PA) noninvasive detection has become a research hotspot of measuring blood glucose concentration
(BGC) in recent years. This novel method overcomes greatly the scattering light interference problem must be faced in
near infrared (NIR) spectroscopy. A PA based BGC measurement set-up was established, in which a Q switched Nd:
YAG pumped optical parametric oscillator (OPO) pulsed laser is used as the excitation source and lateral detection model
was used to detetct the PA signals of glucose. To validate the profile model of real time PA signal, determine the
characteristic wavelengths of glucose, a series of vitro experiments of glucose aqueous solutions were perfromed. Several
wavelengths were preliminarily determined as the characteristic wavelengths via the peak-to-peak values difference. The
prediction concentration model was established via least square fitting algorithm between PA peak-to-peak values with
their different concentrations. The experimental results demonstrated that the PA profile of glucose is consistent with PA
meachnism and the root-mean-squre error (RMSE) of prediction concentration can reach 0.77mmol/L. Therefore, this PA
based set-up and scheme has the potential value in the BGC monitoring research.
Investigation on upconversion luminescence properties of Gd2O3: Ho3+/Yb3+/Tm3+ nanotubes
Show abstract
Lanthanide doped oxides nano materials have novel optical, physical and structural properties. Cubic
Ho3+-Yb3+-Tm3+ co-doped Gd2O3 nanotubes are synthetize by a simple wet-chemical route at low temperature and
ambient pressure followed by subsequent annealing heat treatment in muffle furnace. Nanotubes are formed by adjusting
the pH value of reacting solution. The introduction of Yb3+ leads to strong visible upconversion luminescence and
change the intensity ratio of the green, blue and red luminescence. In trichromatic laser display, research of how to
enhance blue light is in the bottleneck period. In the experiment, the blue emission has been successfully improved. In
certain doping ratio, distinct enhancement of blue emission and obvious degradation of green light have been observed,
which is discussed in detail. X-Ray powder diffraction (XRD), scanning electron microscope (SEM) and upconversion
(UC) emission spectra are used to characterize the sample. Strong and adjusted upconversion luminescence determine
that the nano material is a potential candidate for applications of biological probe, color displays, lighting and photonics.
Space-based laser active imaging simulation system based on HLA
Show abstract
This paper adopts the High Level Architecture to develop the space-based laser active imaging distribution simulation software system, and designs the system framework which contains three-step workflow including modeling, experimental and analysis. The paper puts forward the general needs of the simulation system first, then builds the simulation system architecture based on HLA and constructs 7 simulation federal members. The simulation system has the primary functions of space target scattering characteristic analysis, imaging simulation, image processing and target recognition, and system performance analysis and so on, and can support the whole simulation process. The results show that the distribution simulation system can meet the technical requirements of the space-based laser imaging simulation.
Design and simulation analysis of a magnetic shielding box for ring laser gyroscope
Show abstract
Magnet outside is one of the main reasons that induce the bias shift of the Ring Laser Gyroscope (RLG), and the
most effective way to handle it so far, is to employ a magnetic shielding device. In this paper, we design a new magnetic
shielding box for RLG in Fe-Ni soft magnetic alloy. By 3-D modeling and simulation calculation in finite element
method, we plot the distribution of magnetic flux density of the box in uniform magnet; Besides, distribution of magnetic
shielding effectiveness (SE) on the gaining plane of RLG where is most sensitive to the change of magnet outside, is
given out, too. We also discuss the factors that influence the distribution of SE such as permeability of shielding material,
the thickness of the box and punching on the surfaces of the box. And by the SE test of the box samples, the result of the
simulation analysis was finally proved true. The result shows that, the structure of the box decides the distribution of SE
in it and the permeability of the material plays the predominant role in evaluating the average value of SE. Punching on
the surfaces of the box makes the distribution of SE severely inhomogeneous, and with increase of the permeability, the
influence will be more significant. At last, we put some practical steps forward to enlarge the average value of SE, and
these measures are also applicable in other similar magnetic shielding devices.
Three-dimensional active imaging using compressed gating
Show abstract
Due to the numerous applications employed 3D data such as target detection and recognition, three-dimensional (3D) active imaging draws great interest recently. Employing a pulsed laser as the illumination source and an intensified sensor as the image sensor, the 3D active imaging method emits and then records laser pulses to infer the distance between the target and the sensor. One of the limitations of the 3D active imaging is that acquiring depth map with high depth resolution requires a full range sweep, as well as a large number of detections, which limits the detection speed. In this work, a compressed gating method combining the 3D active imaging and compressive sensing (CS) is proposed on the basis of the random gating method to achieve the depth map reconstruction from a significantly reduced number of detections. Employing random sequences to control the sensor gate, this method estimates the distance and reconstructs the depth map in the framework of CS. A simulation was carried out to estimate the performance of the proposed method. A scene generated by the 3ds Max was employed as target and a reconstruction algorithm was used to recover the depth map in the simulation. The simulation results have shown that the proposed method can reconstruct the depth map with slight reconstruction error using as low as 7% detections that the conventional method requires and achieve perfect reconstruction from about 10% detections under the same depth resolution. It has also indicated that the number of detections required is affected by depth resolution, noise generated by a variety of reasons and complexity of the target scene. According to the simulation results, the compressed gating method is able to be used in the case of long range with high depth resolution and robust to various types of noise. In addition, the method is able to be used for multiple-return signals measurement without increase in the number of detections.
Diffractive imaging analysis of large-aperture segmented telescope based on partial Fourier transform
Show abstract
Large-aperture segmented primary mirror will be widely used in next-generation space-based and ground-based telescopes. The effects of intersegment gaps, obstructions, position and figure errors of segments, which are all involved in the pupil plane, on the image quality metric should be analyzed using diffractive imaging theory. Traditional Fast Fourier Transform (FFT) method is very time-consuming and costs a lot of memory especially in dealing with large pupil-sampling matrix. A Partial Fourier Transform (PFT) method is first proposed to substantially speed up the computation and reduce memory usage for diffractive imaging analysis. Diffraction effects of a 6-meter segmented mirror including 18 hexagonal segments are simulated and analyzed using PFT method. The influence of intersegment gaps and position errors of segments on Strehl ratio is quantitatively analyzed by computing the Point Spread Function (PSF). By comparing simulation results with theoretical results, the correctness and feasibility of PFT method is confirmed.
Improved phase retrieval algorithm for optical imaging systems
Show abstract
The Modified Hybrid-Input-Output (MHIO) phase retrieval algorithm is proposed for wavefront sensing. The results show that the MHIO algorithm significantly outperforms the Modified Gerchberg-Saxton algorithm (MGS) in large noise. However its dynamic-range is lower than MGS algorithm. It also shows that if combine the MGS algorithm with MHIO algorithm, which is called MGS+MHIO algorithm, then it can retain the property of MGS’s high dynamic-range and MHIO’s accuracy so that outperforms either MGS or MHIO algorithm. Repeating simulation results show that MGS+MHIO algorithm improves RMS of phase error obviously in high dynamic range and large noise.
Induced current measurement in bridgewire EED through infrared optical fiber image bundle
Show abstract
While bridgewire electroexplosive device (EED) works in electromagnetic environment, conventional methods can introduce electromagnetism interference. A new method of measuring the induced current in EED is proposed in this article. It bases on infrared imagingto detect the inducting current from long distance and non-contact. The infrared optical fiber image bundle coupling with infrared CCD detector is used to detect the infrared images.At first，the thermal field images are acquired by infrared CCD detector. Then the value of weak induced current of corresponding bridgewire is further determined according to the relations of gray scale values and temperature, temperature and current. The experiment results show that bridgewire current is accurately measured by this method. This method offers a new way to evaluate electromagnetic effect of EED.
Method of high precision interval measurement in pulse laser ranging system
Show abstract
Laser ranging is suitable for laser system, for it has the advantage of high measuring precision, fast measuring speed,no
cooperative targets and strong resistance to electromagnetic interference,the measuremen of laser ranging is the key
paremeters affecting the performance of the whole system.The precision of the pulsed laser ranging system was decided
by the precision of the time interval measurement, the principle structure of laser ranging system was introduced, and a
method of high precision time interval measurement in pulse laser ranging system was established in this paper.Based on
the analysis of the factors which affected the precision of range measure,the pulse rising edges discriminator was
adopted to produce timing mark for the start-stop time discrimination,and the TDC-GP2 high precision interval
measurement system based on TMS320F2812 DSP was designed to improve the measurement precision.Experimental
results indicate that the time interval measurement method in this paper can obtain higher range accuracy. Compared
with the traditional time interval measurement system,the method simplifies the system design and reduce the influence
of bad weather conditions,furthermore,it satisfies the requirements of low costs and miniaturization.
Analytical model of range-Doppler image of rough rotating cones
Show abstract
The technique of laser range-Doppler image has get growing attentions from aerospace and national defense experts.
Recently, in laser range-Doppler image system, laser scatter feature has been used for target ranging and orientation.
Laser range-Doppler image can identify the moving components of the aeroplane, and detect the moving disk and sphere.
Meanwhile, it is also widely used in detection of the moving gesture of the aerospace, discover of the target
micro-motion and the measurement of the local fluid velocity. The laser range-Doppler image of target is the pulse laser
scatter feature of the rotating target, which can reflect the shape, attitude and surface material of the target. For instance,
detection of the flight gesture of target, identification of the warhead, the rotation of structures in a target, and the target
torsional state. An analytical model of laser range-Doppler image of cones rotating around their axes is proposed in this
paper. The analytical model can provide the effects of geometric parameters, the roughness of the surface, attitude and
pulse duration on laser range-Doppler image. This analytical model can degenerate into the analytical model of Doppler
spectra for plane waves. The influences of geometry parameters and attitude are analyzed numerically by using the
analytical model. The results indicate that the laser range-Doppler image of cone can show the information about
geometrical shape and attitude of target. Combining the theory and measurements, the analytical model can be used for
identifying physical parameters and geometrical parameters of cone. This analytical solution may contribute to the laser
Doppler velocimetry and ladar applications.
Guiding pulsed infrared laser radiation using a femtosecond filament array waveguide for the purpose of remote sensing
Show abstract
A hollow cylindrical plasma waveguide, which cladding consists of a large number of a chaotically distributed plasma filaments induced by the propagation of femtosecond (fs) laser pulses in air, is shown to support guided modes of pulsed infrared (IR) laser radiation. Taking into account the discontinuity and the finiteness of the waveguide cladding, the loss coefficient loss of the laser radiation is calculated for different spatial configurations. We report how the waveguide loss depends on its structural parameters like normalized plasma diameter, distance between filaments, core-radius, cladding’s thickness, and filaments’ electron density. For typical plasma parameters, the loss of the fs plasma waveguide is found to be lower than that of freely propagating IR laser beams to distances in the order of the filamentation length. This fact allows the delivery of collimated pulsed laser light over long distances in atmospheric air, which is necessary for optical-based remote sensing and the detection of chemical and biological agents.
Phase retrieval based on the Wigner distribution
Show abstract
The Gerschberg-Saxton (GS) algorithm is a classic algorithm for phase retrieval. It is usually based on FFT (fast Fourier
transform) and IFFT (inverse fast Fourier transform). We improve the GS algorithm based on the Wigner distribution.
Instead of FFT and IFFT, Wigner distribution is not only used in the propagation but also filtered to optimize the signal
during the iteration. The simulation results illustrate that the new method could effectively improve the efficiency and
accuracy of phase retrieval.
Range walk error correction using prior modeling in photon counting 3D imaging lidar
Show abstract
A real-time correction method for range walk error in photon counting 3D imaging Lidar is proposed in this paper. We establish the photon detection model and pulse output delay model for GmAPD, which indicates that range walk error in photon counting 3D imaging Lidar is mainly effected by the number of photons during laser echo pulse. A measurable variable – laser pulse response rate is defined as a substitute of the number of photons during laser echo pulse, and the expression of the range walk error with respect to the laser pulse response rate is obtained using priori calibration. By recording photon arrival time distribution, the measurement error of unknown targets is predicted using established range walk error function and the range walk error compensated image is got. Thus real-time correction of the measurement error in photon counting 3D imaging Lidar is implemented. The experimental results show that the range walks error caused by the difference in reflected energy of the target can be effectively avoided without increasing the complexity of photon counting 3D imaging Lidar system.
Influence of geomagnetic field for continuous wave (CW) laser excited sodium guide stars backward fluorescence intensity
Show abstract
Recent years, benefited from their greater coverage and smaller focus anisoplanatism, sodium laser guide stars are
becoming more attractive in providing artificial beacons for adaptive optical (AO) system in large ground telescopes
compared to Rayleigh guide stars. And it had been found that the Sodium laser guide stars backward fluorescence
intensity is closely related with the local magnetic field intensity and direction. In this paper, we make use of the World
Magnetic Model (WMM) 2010 and by considering the geographical differences in Beijing, Nanjing and Kunming we
investigate the effects of the light intensity, line-width, polarization of the CW laser and re-pumping conditions on the
photon return flux by numerically solving the Rochester et al. Bloch model. So in theory we can get better Sodium guide
star in Beijing. In conclusion, according to the simulation results, we can acquire much bright of Sodium guide stars by
optimize the parameter of the launched 589 nm laser.
Investigation of optical nonlinear properties in semiconductor GaN
Show abstract
The optical nonlinearities of bulk GaN single crystal are investigated by conducting Z-scan experimental measurements, using nanosecond pulses at 532nm. The material’s nonlinear absorptive and refractive optical nonlinearities are determined by measuring the normalized transmittance with and without an aperture in the far field. After simulating the experimental curves, the two-photon absorption (TPA) coefficient, especially the refractive-index change induced by two-photon-excited free carrier, are obtained. The experimental results show that GaN has reverse saturable absorption and self-defocusing effect at 532 nm, indicating this material is a good candidate for future photonics applications. The theoretical simulation fit well with experimental results.
Profile detection system for transparent parts' shaping
Show abstract
An automatically detecting system for the shaping of transparent parts is designed and achieved. The
system is based on detecting laser spots for profile shaping. During the transmission of the laser beam
conveyed on the surface of transparent parts emitted from a He-Ne laser, the laser spot is captured by a
CCD (Charge-coupled Device) camera. When the transparent part is shaped, the laser beam is blocked
by parts and the laser spot decreases. Three key points on the surface of transparent part is monitored
from three lasers, which realize the flexible forming of transparencies. Moreover, the inspection of
changing laser spot is investigated, and the basis points of lasers and CCD cameras in horizontal and
vertical direction are located by mechanical devices. The whole measurement for the profile detection
of laser spot includes four steps: image capturing, image preprocessing, contour extracting and
selecting, fitting and calculating. The changes of laser spot can be measured and the threshold value
can be converted into the control of transparent parts’ shaping based on the mathematical method.
Using the proposed method, a real transparent object is measured. Experimental results show that the
proposed measurement system is effective and feasible.
Optimization of reconstructed images of 3D phase hologram based on phase-only spatial light modulator
Show abstract
Based on the existed ways of 2-D reconstructed images by spatial light modulator (SLM), the methods to enhance the reconstructed quality of 3-D images are investigated in this paper. Based on the diffraction theory, the effects of a lattice SLM with a limited fill factor on the reconstructed images are analyzed. Through adding the phase of the convergent spherical wave, the two focused planes of reconstructed images and the multi-order beams caused by the lattice structure of the SLM can be separated spatially. Therefore, the spatial filter is used to eliminate the influences of higher-orders diffraction beams and zero-order light of reconstructed images, respectively. A holographic optoelectronic display system based on liquid crystal spatial light modulator (LC-SLM) is set up to demonstrate this method.
High delay precision based on dynamic phase-shift for range-gated laser imaging technology
Show abstract
The range-gated laser imaging technology has become a useful technique in many applications in recent years. In
order to expand the range of imaging detection and improve the measurement range resolution of the imaging system, we
used circular step advance delay sequence for the synchronous control. And we developed a method of using dynamic
phase-shift technique in FPGA to improve the precision of the delay in the time sequence, which can make the precision
of the delay stepper between the two adjacent frames less than global clock period of the FPGA and approach the limit of
FPGA’s operating frequency. That is to say, it can equivalently increase the clock frequency. Then we can effectively
improve measurement range resolution of the imaging system. In this paper, we have studied how dynamic phase-shift
technique can be equivalent to higher clock frequency and performed some experiments. We presented the structure of
dynamic phase-shift technique used to improve the precision of delay in the synchronization control time sequence. And
the simulation and experimental results are showed in this paper. The results demonstrate that using dynamic phase-shift
technique in FPGA can make the precision of the delay between the ICCD’s trigger pulse and the laser’s trigger pulse
reach 1ns, which means the resolution of measurement range can be 0.15m theoretically. The timing control signal with
dynamic phase-shift technique designed in this paper can be widely used in range-gated imaging because of its high
timing control precision and flexible parameter setting.
Speckle pattern rotation and a detection scheme for its rotation angle
Show abstract
When coherent light beams, i.e., laser beams are transmitted in an optical fiber and exit from one end to form an output light spot on a screen, non-uniform intensity distribution called speckle patterns is often recognized in the output light spot. The authors have confirmed that when a multimode optical fiber is placed in a loop or a U-shape onto a support plate and the support plate is rotated or tilted with the diameter of the loop or the longitudinal axis of the U-shape as the axis of the rotation or tilting motion, the speckle patterns appear to rotate in a certain direction. Such rotation phenomena of speckle pattern are observed with relatively good reproducibility, and the rotation angle of the speckle pattern is almost in proportion to the rotation or tilting angle of the support plate. In the authors’ previous reports, a rotation angle of speckle pattern was detected by manual work, which was tiresome and time-consuming task. This was also unrealistic if we are going to utilize the phenomena for some kinds of sensing application. In this paper, a new scheme for semi-automatically detecting the rotation angle of speckle pattern from image data before and after the pattern rotation is being tried. With this scheme, detection of the pattern rotation angle upon rotation or tilting of the support plate can be realized easily in a short period of time. The semi-automatic detection scheme has been actually employed to investigate rotation characteristics of speckle pattern in several different conditions.
Single particle sizing approach using angular optical scattering distributions
Show abstract
Sizing a small particle from its scattered field has been a long-standing problem. Popular established methods require a priori knowledge of either the refractive index of the particle, or the approximate particle size range. In this paper, the diffraction tomography (DT) theory is studied and a single particle sizing approach using angular optical scattering field is proposed. There is a Fourier relationship between the scattering amplitude in the far zone and the scattering potential of the scatterer, under the 1st-order Born approximation for weakly scattering. Based on this relationship, the distribution of scattering potential can be retrieved from angular resolved scattered field by the use of a fast Fourier transform. Single particle size is estimated from the scattering potential. Numerical simulations for spherical particles are presented and discussed. Simulation results show that in the case of low contrast, the size of the particles can be estimated accurately in the presence of moderate noise. A further variant of this algorithm based on Rytov approximation is also discussed.
Study of UV imaging technology for noninvasive detection of latent fingerprints
Show abstract
Using UV imaging technology, according to the special absorption 、reflection 、scattering and fluorescence characterization of the various residues in fingerprints (fatty acid ester, protein, and carboxylic acid salts etc) to the UV light, weaken or eliminate the background disturbance to increase the brightness contrast of fingerprints with the background, and design、setup the illumination optical system and UV imaging system, the noninvasive detection of latent fingerprints remaining on various object surface are studied. In the illumination optical system, using the 266nm UV Nd:YAG solid state laser as illumination light source, by calculating the best coupling conditions of the laser beam with UV liquid core fiber and analyzing the beam transforming characterizations, we designed and setup the optical system to realize the UV imaging uniform illumination. In the UV imaging system, the UV lens is selected as the fingerprint imaging element, and the UV intensified CCD (ICCD) which consists of a second-generation UV image intensifier and a CCD coupled by fiber plate and taper directly are used as the imaging sensing element. The best imaging conditions of the UV lens with ICCD were analyzed and the imaging system was designed and setup. In this study, by analyzing the factors which influence the detection effect, optimal design and setup the illumination system and imaging system, latent fingerprints on the surface of the paint tin box、plastic、smooth paper、notebook paper and print paper were noninvasive detected and appeared, and the result meet the fingerprint identification requirements in forensic science.
A display technology based on Fabry Perot interferometer array
Show abstract
The performances of a display chip based on Fabry-Perot interferometer (FPI) array was stimulated theoretically.
Lighting by a single frequency laser, the grayscale of image pixels can be manipulated by transmission intensity
modulation of the FPIs which act as chip pixels. The F-P cavities were constructed by Lithium Niobate thin layer. The
cavity mirrors were deposited directly on the crystal surfaces. Using the converse piezoelectric effect of Lithium Niobate,
the cavity length was scanned by changing the applied voltage. Therefore, the single frequency laser transmission was
controlled. The electrodes were coated locally for corresponding chip pixel. A theoretical model for a display chip with
an array of 64×64 FPIs was built. The main parameters of the chip were optimized and the performances were stimulated.
The influences of mirror flatness, parallel of the cavity mirrors, linewidth and frequency stability of the lighting laser
were discussed. The simulation results indicated that this technique is promising for laser display.
Single photon ranging system using two wavelengths laser and analysis of precision
Show abstract
The laser ranging system based on time correlation single photon counting technology and single photon detector has the feature of high precision and low emergent energy etc. In this paper, we established a single photon laser ranging system that use the supercontinuum laser as light source, and two wavelengths (532nm and 830nm) of echo signal as the stop signal. We propose a new method that is capable to improve the single photon ranging system performance. The method is implemented by using two single-photon detectors to receive respectively the two different wavelength signals at the same time. We extracted the firings of the two detectors triggered by the same laser pulse at the same time and then took mean time of the two firings as the combined detection time-of-flight. The detection by two channels using two wavelengths will effectively improve the detection precision and decrease the false alarm probability. Finally, an experimental single photon ranging system was established. Through a lot of experiments, we got the system precision using both single and two wavelengths and verified the effectiveness of the method.
The design of infrared laser radar for vehicle initiative safety
Show abstract
Laser radar for vehicle is mainly used in advanced vehicle on-board active safety systems, such as forward anti-collision systems, active collision warning systems and adaptive cruise control systems, etc. Laser radar for vehicle plays an important role in the improvement of vehicle active safety and the reduction of traffic accidents. The stability of vehicle active anti-collision system in dynamic environment is still one of the most difficult problems to break through nowadays. According to people’s driving habit and the existed detecting technique of sensor, combining the infrared laser range and galvanometer scanning technique , design a 3-D infrared laser radar which can be used to assist navigation, obstacle avoidance and the vehicle’s speed control for the vehicle initiative safety. The device is fixed to the head of vehicle. Then if an accident happened, the device could give an alarm to remind the driver timely to decelerate or brake down, by which way can people get the purpose of preventing the collision accidents effectively. To accomplish the design, first of all, select the core components. Then apply Zemax to design the transmitting and receiving optical system. Adopt 1550 nm infrared laser transmitter as emission unit in the device, a galvanometer scanning as laser scanning unit and an InGaAs-APD detector as laser echo signal receiving unit. Perform the construction of experimental system using FPGA and ARM as the core controller. The system designed in this paper can not only detect obstacle in front of the vehicle and make the control subsystem to execute command, but also transfer laser data to PC in real time. Lots of experiments using the infrared laser radar prototype are made, and main performance of it is under tested. The results of these experiments show that the imaging speed of the laser radar can reach up to 25 frames per second, the frame resolution of each image can reach 30×30 pixels, the horizontal angle resolution is about 6. 98mrad, the vertical angle resolution is about 3. 49mrad, the maximum value of range error is 0. 5m, minimum value is 0. 07m at the detectable distance range 10-200m and the detection probability is more than 99. 9%.
Analyses of spectral ripple phenomenon in the optical-feedback cavity ring-down spectroscopy
Show abstract
Based on the vector scattering theory, we analyze and discuss the interference effect of the surface scattering lights on the folded mirror of V-shaped cavity. It is found that the interference effect can introduce the periodic fluctuation of scattering loss, and this phenomenon is similar with the spectral ripple effect existed in optical-feedback Cavity Ring-down Spectroscopy (CRDS). We believe that the interference effect of the scattering lights on folded mirror is an important source of spectral ripple effect, and it can be used to explain the mechanism of spectral ripple phenomenon.
Study on the algorithm in the measurement of large annular planes with a laser tracker
Wen Zhu,
Tian-quan Fan,
Xue-dong Cao,
et al.
Show abstract
To measure the flatness of the large annular planes, a method with laser tracker on the basis of multi-station and time-sharing measurement principle is proposed in this paper. The laser tracker is used to measure the flatness of large annular planes at different base stations. Based on the redundancy principle, the space coordinates of each measuring point can be determined by large amount of measured data. In the paper, the results of computer simulation for the principle are obtained with several iterative nonlinear algorithms, and it is shown that the method is feasible.
Cat-eye target imaging system research and dual-channel DSP implementation
Show abstract
In modern warfare, well-equipped and trained snipers have become a mortal malady for the combat troops. How to accurately, timely and quickly find and destroy snipers becomes a research focus of national military experts. In order to effectively detect faint echo signal of cat-eye target and get the snipers’ position information in the detection area, a small size of dual-channel active laser detection system with monochrome and color Charge-couple Devices(CCD) is designed, which is based on the laser imaging principle of cat-eye effect, associated tests are also conducted. The dual-channel video capture can obtain more information of target area, while taking advantage of the high sensitivity of monochrome CCD will also provide more accurate grayscale information for the video image processing. In order to achieve the miniaturization of system, we choose a video processing board whose size is only 54mm*90mm as hardware platform to complete the algorithm. For verifying the feasibility and accuracy of algorithm, we ultimately build a full set of experimental detection system. The test results show that the system can accurately detect and mark typical cat-eye target from background under different distances, which verifies the rationality and validity of the proposed system and has certain practicality and promotion in the active laser detection system research areas.
Error separation technique for measuring aspheric surface based on dual probes
Show abstract
In this paper, we present an error separation method based on dual probes for the swing arm profilometer to calibrate the rotary table errors. Two probes and the rotation axis of swinging arm are in a plane. The scanning tracks cross each other as both probes scan the mirror edge to edge. Since the surface heights should ideally be the same at these scanning crossings, this crossings height information can be used to calibrate the rotary table errors. But the crossings height information contains the swing arm air bearing errors and measurement errors of probes. The errors seriously affect the correction accuracy of rotary table errors. The swing arm air bearing errors and measurement errors of probes are randomly distributed, we use least square method to remove these errors. In this paper, we present the geometry of the dual probe swing arm profilometer system, and the profiling pattern made by both probes. We analyze the influence the probe separation has on the measurement results. The algorithm for stitching together the scans into a surface is also presented. The difference of the surface heights at the crossings of the adjacent scans is used to find a transformation that describes the rotary table errors and then to correct for the errors. To prove the error separation method based on a dual probe can successfully calibrate the rotary table errors, we establish SAP error model and simulate the effect of the error separation method based on a dual probe on calibrating the rotary table errors.
Target model and simulation for laser imaging fuze
Show abstract
Image detection is an important direction of fuze development nowadays, and laser imaging fuze is one of the main technologies. This paper carries out the research in simulation technology of the process with detection, scan and imaging, which is used in laser imaging fuze for tank target, and get the simulation images information of different intersection conditions, including tank spot information，distance information and power information. The target coordinate system is established with the movement characteristics，physical characteristics and existing coordinate system of tank target. And through transferring missile coordinates to the target coordinate system as well as the relative movement between the different time intervals, the model of missile-target in time and space is build up. The model is build up according to the tank target and diffusion properties of different background, including desert, soil, vegetation, and buildings. The relations of scattering power and bidirectional reflectance distribution function deduced the laser echo power calculation formula, which can calculate the echoes incidence to each surface of the laser.The design of laser imaging fuze simulation system is complicated ,which contains the technology of the process with detection, scan and imaging used in laser imaging fuze for tank target. The simulation system products the tank spot picture, the distance gradation picture, and the power gradation picture. The latter two contains two-dimensional information, the scanning distance as well as the value of echo power to meet the expected design effects.
A simple accurate algorithm for the critical angle refractometer
Show abstract
We present a fast, simple, sub-pixel algorithm on the critical angle refractometer to measure the refractive index of the liquid sample by determining the centroid of the light intensity of the relative reflective curve. The centroid algorithm utilizes a divergent fiber-coupled royal blue LED source to irradiate on the dielectric surface between the prism and the media, which generates the light intensity distribution of the reflectance facula. Instead of the critical angle pixel as the differential algorithm and the threshold algorithm, the sub pixel centroid algorithm is based on calculating the centroid value of the light intensity of the relative reflective curve. In some moderate turbid solutions, the centroid algorithm is less sensitive to the scattering and absorption than the differential algorithm and the threshold algorithm. It is possible to utilize the centroid point of the relative reflective curve to determine the refractive index. Supported by the theoretical analysis and experimental results on saline solutions, we can conclude that the proposed algorithm is effective to get the super resolution and meaningful to the refractive index measurement of the liquid. The critical angle refractometer with this centroid method is potential to be a high-accuracy, high-resolution, and reliable automatic refractometer.
Determination of geometrical form factor in coaxial lidar system
Show abstract
In recent years, lidar system has become a very successful tool in environmental exploration and remote sensing of the atmosphere. However, geometric form factor, which is inherently determined by the lidar structure, restricts the accuracy of the lidar data at nearby distances. In order to get the effective atmospheric parameter information close to the ground from lidar system, it is essential to obtain its geometric form factor. The ratio of the energy received by the photo detector to the energy reached the telescope primary mirror is defined as geometric form factor, which is affected by three facts. First, the overlap of the transmitted beam with the receiver system is often incomplete, so only a part of the return signal goes into the receiving telescope. Second, the backscattering signals from small and medium distances can not be focused well on the focal plane, so only part of them can be sensed by the detector. Third, the obstruction of the secondary mirror can also increase the light loss. By analyzing these three facts, we described a geometric optical calculative method for determining the geometrical form factor in a Cassegrain telescope system. By reviewing the structure of the coaxial and biaxial transmitter and receiver system, and considering the above three reasons, a simple model is applied to demonstrate the image formation of a circular object of diameter G positioned a distance R close to a lidar detection unit. Then the position between the illumination e of the focal plane and telescope aperture s is discussed, and a function to describe the geometrical form factor can thus be derived in both coaxial and non-coaxial lidar cases. Finally, two different lidar systems are compared with simulation method in order to validate the proposed model.
Comparisons between field-widen Michelson interferometer and Fabry-Perot interferometer as the spectroscopic filter in high spectral resolution lidar
Show abstract
One of the pivotal challenges in high spectral resolution lidars (HSRLs) is the spectral discrimination process, which brings about more straightforward and accurate retrieval without a priori assumptions in contrast to standard backscatter lidars. Inteferometric filters such as Fabry-Perot interferometer (FPI) has shown great convenience for spectrally separating the Rayleigh and Mie scattered elements in HSRL returned signals. Based on interference of two incident beams, the field -widen Michelson interferometer (FWMI) may be also the same potential in this application as FPI in spite of some performance differences. In this paper, we concentrate on the performance comparisons of FWMI with FPI as spectroscopic filter in HSRL from the inspections of spectral discrimination characteristic, field of view (FOV) tolerance, the efficiency of power collection, etc. All these analytical comparisons are quantificational and will be beneficial to reasonable choice among the two optical filters for HSRL. The results indicate that in spite of a litter lower transmittance when processing the radiation with very small divergence and more rigorous tolerance for temperature stability and surface flatness compared with FPI, FWMI is still very competent in this spectral filtering process for its remarkable spectral discrimination characteristic and efficient photons collective ability which attributes to its field widen design and intrinsically outstanding spectral separation performance.
Research on long-range laser active imaging system applied in adverse weather conditions
Show abstract
A low-light level night vision device or thermal infrared imager belonging to passive imaging system is generally
used in daily target detection and identification. But in adverse weather conditions of dark of night, poor atmospheric
transmission characteristics or strong backscattering (fog, dust, rain, snow, etc.), even the most sensitive low-light level
night vision could not provide enough image resolution for detecting and identifying targets, and the thermal infrared
imager is also limited by low temperature contrast. A long-range laser active imaging system, in combination with
high-power semiconductor pulsed lasers with collimation technology, receiving objective lens of large diameter, long
focal length and narrow viewing angle, high-gain image intensifier CCD (ICCD) camera and range-gated
synchronization control technology, is developed for long distance target detection and high resolution imaging in
adverse weather conditions. The system composition and operating principle are introduced. The extremely powerful and
efficient illuminators with collimation technology are able to deliver uniform beams, which are essential for illuminating
targets at a distance and generating high-quality images. The particular receiving objective lens, ICCD camera and
range-gated synchronization control technology could reduce strong backscattering signal and improve imaging
signal-to-noise ratio. The laboratory and outfield experiments have been done to validate imaging effect and imaging
quality. The results show that the minimum resolution is about 3-5cm, 10cm, and greater than 20 cm for target far from
1100m, 4700m, and 6700m respectively in dark of night. Furthermore, the minimum resolution could reach to 10cm and
20cm for target far from 2500m and 4800m respectively and the image is too blurred to accurately identify the target
when observing the target far from 7200m in rainy condition.
Research of application of high-repetition-rate green laser in underwater imaging system
Show abstract
It is commonly known that absorption and scattering are the main causes of reducing performance of imaging system, especially imaging distance and resolution. Generally, various techniques are applied to decrease the effect of scattering, such as synchronous scanning and range-gated technique. Continuous-laser imaging technique meets requirements of imaging objects in the large field of view in real time, but imaging distance is less than 2 attenuation lengths in natural water. High-repetition-rate green laser, called quasi-continuous wave (QCW) green laser, is a better light source for underwater imaging. It has 1 kHz-100 kHz modulated rate, and its single pulse peak power is KW magnitude, which can be applied to range-gated imaging as Canadian LUCIE system. In addition, its polarization property is excellent for underwater polarization imaging. Therefore, it has enormous potential to underwater imaging. In order to realize its performance in underwater imaging system, we setup a separated underwater staring imaging system. For this system, a theoretic model is built by the lidar equation and optic transmission theory, and the system is evaluated by modulation transfer function (MTF). The effects of laser and receiver’s parameters for the system are analyzed. Then the comparative experiments are conducted in turbid water in laboratory. The results indicate that high pulse energy improves imaging distance. Aperture and polarization could reduce the effect of scattering effectively in staring system. The result shows that this underwater system performs better by choosing suitable parameters of source and receiver.
Optical nonlinear properties of a new porphyrin compound
Show abstract
A new organic material 4-hydroxy-ethyl-phenyl-porphyrin-3-propionate was investigated due to its favorable nonlinear absorptive and refractive properties using a modified time-resolved pump-probe system with phase object at 532 nm under picosecond pulse excitation. A five-level model was used to explain the optical nonlinearity of the sample. With the corresponding fitting program, the nonlinear coefficients of the sample were obtained.
Schematic of space-borne lidar surveying neritic seabed terrain
Show abstract
Light Detection and Ranging (LiDAR) is a kind of new technical fast developing from 1960s especially in last 30
years. This technical processes high measurement accuracy, high resolution, powerful recognition capability and
anti-interference capability. Space-Borne LiDAR which had wide field of view caused the big astronautic countries more
attention, and it became an important part of global 3-D terrain detection, aerosphere detection, wind velocity detection,
imagination and rendezvous and docking. In this paper, water depth measurement technology with airborne LiDAR was
summarized. Neritic seabed terrain detection schematic was put forward, and then the key components and the different
points of the schematic were analyzed. Pertinence suggestions were described in this paper which could supply further
research on space-borne LiDAR.The space-borne laser emits several beams which form laser array, and detects the
ground target by one dimension scanning. The laser includes multiple-beam emission system and multiple-signal
reception system, but no flexible components in order to increasing the system dependability. The multiple-beam mode
can make an observably increase of detection efficiency comparing with the single-beam mode. Each single laser pulse
can return several different distance signals, so the repeat frequency can be lower. The laser pulse can be reflected by the
sea surface and neritic seabed, so the depth can be calculated by the two reflection signals. The space-borne LiDAR data
can be used to analyze sea gravitational field, change of the sea level and tide, sea weather and thickness of ice band.
Damage effect on CMOS detector irradiated by single-pulse laser
Show abstract
Imaging systems are widespread observation tools used to fulfill various functions such as recognition, detection and
identification. These devices such as CMOS and CCD can be damaged by laser. It is very important to study the damage
mechanism of CMOS and CCD. Previous studies focused on the interference and damage of CCD. There were only a
few researches on the interaction of CMOS and the laser.
In this paper, using a 60ns, 1064 nm single-pulse laser to radiate the front illuminated CMOS detector, the typical
experiment phenomena were observed and the corresponding energy density thresholds were measured. According to the
experiment phenomena, hard damage process of CMOS can be divided into 3 stages. Based on the structure and working
principle of CMOS, studying the damage mechanism of 3 stages by theoretical analysis, point damage was caused by the
increase in leakage current due to structural defects resulting from thermal effects, half black line damage and black lines
cross damage were caused by signal interruption due to that the device circuit fuses were cut. Enhancing the laser energy
density, the damaged area expanded. Even if the laser energy density reached 1.95 J/cm2, black lines has covered most of
the detector pixels, the detector still not completely lapsed, the undamaged area can imaging due to that pixels of CMOS
were separated with each other. Experiments on CMOS by laser pulses at the wavelength of 1064 nm and the pulse
duration in 25ps was carried out, then the thresholds with different pulse durations were measured and compared.
Experiments on CMOS by fs pulsed laser at the frequency of 1 Hz, 10 Hz and 1000 Hz were carried out, respectively, the
results showed that a high-repetition-rate laser was easier to damage CMOS compared to single-shot laser.
A novel building boundary reconstruction method based on lidar data and images
Show abstract
Building boundary is important for the urban mapping and real estate industry applications. The reconstruction of building boundary is also a significant but difficult step in generating city building models. As Light detection and
ranging system (Lidar) can acquire large and dense point cloud data fast and easily, it has great advantages for building
reconstruction. In this paper, we combine Lidar data and images to develop a novel building boundary reconstruction
method. We use only one scan of Lidar data and one image to do the reconstruction. The process consists of a sequence of three steps: project boundary Lidar points to image; extract accurate boundary from image; and reconstruct boundary
in Lidar points. We define a relationship between 3D points and the pixel coordinates. Then we extract the boundary in the image and use the relationship to get boundary in the point cloud. The method presented here reduces the difficulty of data acquisition effectively. The theory is not complex so it has low computational complexity. It can also be widely used
in the data acquired by other 3D scanning devices to improve the accuracy. Results of the experiment demonstrate that
this method has a clear advantage and high efficiency over others, particularly in the data with large point spacing.
The research of precision timing measurement in application of TDC_GP2 in laser ranging
Show abstract
Laser ranging could measure the distance between laser range finder and detection target by calculate the
flight time of laser. The laser of laser range finder adopt semiconductor pump laser of 1064nm, PerkinElmer C30659
APD was used in photoelectric detection circuit, STC89C52 MCU and the FPGA of XC3S400 were used as the core of
control system. High precision time interval measurement is one of the most important techniques in laser ranging. In
this paper, we adopt a high precision time interval measurement time to digital converter chip of ACAM corporation in
Germany. TDC_GP2 is the next generation of Acam general-purpose TDCs, higher resolution and smaller package size
make it ideal for cost sensitive industrial applications. We select the measurement range 2 of the TDC_GP2, and the
maximum time resolution is 65ps. Digital TDCs use internal propagation delays of signals through gates to measure time
intervals with very high precision. Through researching the working principle of TDC_GP2, hardware circuit diagram of
TDC_GP2、measurement time diagram of TDC_GP2、the system software design of TDC_GP2, and applying in the
different measuring distances and different time measurement temperatures, research shows that the precision of time
measurement lies on the different measuring distances and different time measurement temperatures. In the end, we
make some suggestions of improving the precision of time measurement.
Investigation of range accuracy of gain-modulated laser range imaging
Chen-fei Jin,
Zi-tong Song,
Si-qi Zhang,
et al.
Show abstract
A gain-modulated laser range imaging technology is generalized and its range accuracy is deduced. Theoretical results
indicate that the range accuracy is proportional to the ratio of gain function to the derivative of the gain function and
inverse proportional to output SNR. A gain-modulated laser range imaging system is established in our laboratory. It
consists of a pulsed laser which is capable of generating laser pulses with a pulse width of 10ns and a center wavelength
of 532 nm, and a receiver which is a digital 256×256 CCD sensor coupled to a GEN II intensifier with a 10nm bandwidth
optical filter. Image intensifier is electronically driven and can be set to three modulated gain or constant gain. A range
image of the target can be extracted by processing an intensity image with modulated gain and an intensity image with
constant gain. Some indoor experiments are performed with sinusoidal, linear and exponential gain functions. The range
images of the targets from 52 m to 58 m is taken and analyzed. Experimental results demonstrate the range accuracy with
both sinusoidal and linear gain function depends on the relative range but one with exponential gain function
independent of relative range. Specially, in the exponential gain function case the relatively small time constant can
contribute to relatively high range accuracy.
The technology on noise reduction of the APD detection circuit
Show abstract
The laser pulse detection is widely used in the field of laser range finders, laser communications, laser radar, laser Identification Friend or Foe, et al, for the laser pulse detection has the advantage of high accuracy, high sensitivity and strong anti-interference. The avalanche photodiodes (APD) has the advantage of high quantum efficiency, high response speed and huge gain. The APD is particularly suitable for weak signal detection. The technology that APD acts as the photodetector for weak signal reception and amplification is widely used in laser pulse detection. The APD will convert the laser signal to weak electrical signal. The weak signal is amplified, processed and exported by the circuit. In the circuit design, the optimal signal detection is one key point in photoelectric detection system. The issue discusses how to reduce the noise of the photoelectric signal detection circuit and how to improve the signal-to-noise ratio, related analysis and practice included. The essay analyzes the mathematical model of the signal-to-noise ratio for photoelectric conversion and the noise of the APD photoelectric detection system. By analysis the bandwidth of the detection system is determined, and the circuit devices are selected that match the APD. In the circuit design separated devices with low noise are combined with integrated operational amplifier for the purpose of noise reduction. The methods can effectively suppress the noise, and improve the detection sensitivity.
The application of camera calibration in range-gated 3D imaging technology
Show abstract
Range-gated laser imaging technology was proposed in 1966 by LF Gillespiethe in U.S. Army Night Vision Laboratory(NVL). Using pulse laser and intensified charge-coupled device(ICCD) as light source and detector respectively, range-gated laser imaging technology can realize space-slice imaging while restraining the atmospheric backs-catter, and in turn detect the target effectively, by controlling the delay between the laser pulse and strobe. Owing to the constraints of the development of key components such as narrow pulse laser and gated imaging devices, the research has been progressed slowly in the next few decades. Until the beginning of this century, as the hardware technology continues to mature, this technology has developed rapidly in fields such as night vision, underwater imaging, biomedical imaging, three-dimensional imaging, especially range-gated three-dimensional(3-D) laser imaging field purposing of access to target spatial information. 3-D reconstruction is the processing of restoration of 3-D objects visible surface geometric structure from three-dimensional(2-D) image. Range-gated laser imaging technology can achieve gated imaging of slice space to form a slice image, and in turn provide the distance information corresponding to the slice image. But to inverse the information of 3-D space, we need to obtain the imaging visual field of system, that is, the focal length of the system. Then based on the distance information of the space slice, the spatial information of each unit space corresponding to each pixel can be inversed. Camera calibration is an indispensable step in 3-D reconstruction, including analysis of the internal structure of camera parameters and the external parameters . In order to meet the technical requirements of the range-gated 3-D imaging, this paper intends to study the calibration of the zoom lens system. After summarizing the camera calibration technique comprehensively, a classic calibration method based on line is selected. One-to-one correspondence between visual filed and focal length of system is obtained and offers effective visual field information for the matching of imaging filed and illumination filed in range-gated 3-D imaging technology. On the basis of the experimental results, combined with the depth of field theory, the application of camera calibration in range-gated 3-D imaging technology is futher studied.
Edge features extraction from 3D laser point cloud based on corresponding images
Show abstract
An extraction method of edge features from 3D laser point cloud based on corresponding images was proposed. After the registration of point cloud and corresponding image, the sub-pixel edge can be extracted from the image using gray moment algorithm. Then project the sub-pixel edge to the point cloud in fitting scan-lines. At last the edge features were achieved by linking the crossing points. The experimental results demonstrate that the method guarantees accurate fine extraction.
Automatic road extraction for airborne lidar data
Show abstract
Airborne LiDAR, as a precise and fast earth’s surface three-dimensional (3D) measuring method, has been widely used in the past decades. It provides a new approach for acquiring road information. By analyzing the characteristics of LiDAR datasets as well as that of the road in the datasets, a morphological method has been proposed to automatically extract the road from airborne LiDAR datasets. Firstly, ground points are segmented from raw LiDAR data by morphological operations. The key factor in this process is how to select the window sizes in different scale spaces, and setting the elevation threshold to prevent over-segmentation in each scale space. Secondly, candidate road points are segmented from the ground points, which are obtained from previous step, by intensity constraint, local point density and region area constraint, and so on. Thirdly, morphological opening operation and closing operation were used to process the candidate road points segmented from above steps. The opening operation may effectively filter the noise areas, and greatly maintain the road detail. The closing operation may fill the small holes within the road, connecting nearby roads, and smoothing the road boundary, without signification area change. The main road can be extracted from the raw airborne LiDAR points by previous three steps. Finally, the proposed method has been verified by LiDAR data which consists of complex road networks. The result shows that the proposed method can automatically extract road from airborne LiDAR data with higher efficiency and precision.
Modeling and comparative study of various detection techniques for FMCW LIDAR using optisystem
Show abstract
In this paper we investigated the different detection techniques especially direct detection, coherent heterodyne detection and coherent homodyne detection on FMCW LIDAR system using Optisystem package. A model for target, propagation channel and various detection techniques were developed using Optisystem package and then a comparative study among various detection techniques for FMCW LIDAR systems is done analytically and simulated using the developed model. Performance of direct detection, heterodyne detection and homodyne detection for FMCW LIDAR system was calculated and simulated using Optisystem package. The output simulated performance was checked using simulated results of MATLAB simulator. The results shows that direct detection is sensitive to the intensity of the received electromagnetic signal and has low complexity system advantage over the others detection architectures at the expense of the thermal noise is the dominant noise source and the sensitivity is relatively poor. In addition to much higher detection sensitivity can be achieved using coherent optical mixing which is performed by heterodyne and homodyne detection.
LRCS calculation and imaging of complex target based on GRECO
Show abstract
The research on Laser Radar Cross Section(LRCS) is of great significance in many research fields, such as defense, aviation, aerospace, meteorology etc. Current study of LRCS focuses mainly on the full-size target. The LRCS of full-size target, characterized by the scattering properties of the target, is influenced by target material, shape, size, and the wavelength of laser, but it is independent on the size of irradiation beam. In fact, when the target is in large size, and the beam emitted from laser radar is very narrow, it may be in a local rather than a full-size irradiation. In this case, the scattering properties of a target are dependent on not only the size of irradiation beam on the target, but also the direction of irradiation beam. Therefore, it is essential to analyze the scattering properties of a complex target in a local irradiation. Based on the basic theory of Graphic-electromagnetic Computing(GRECO), we improved the method used in the processing of electromagnetic scattering, calculated the monostatic and bistatic LRCS of several targets. The results are consistent with that in the early work done by other researchers. In addition, by changing the divergence angle of the incident beam, the situation of narrow beam in a local irradiation was presented. Under different sizes of irradiation beam, analysis and calculation of local cross section was made in detail. The results indicate that the size of irradiation beam can greatly affect the LRCS for targets. Finally, we calculated scattering cross section per unit of each location point; with color tag, scattering intensity distribution of every location point on the target was displayed, which can be revealed by the color of every pixel point. On the basis of scattering intensity distribution of every location point, the imaging of a target was realized, which provides a reference for quick identification of the target.
The research of knitting needle status monitoring setup
Show abstract
In textile production, quality control and testing is the key to ensure the process and improve the efficiency. Defect of the knitting needles is the main factor affecting the quality of the appearance of textiles. Defect detection method based on machine vision and image processing technology is universal. This approach does not effectively identify the defect generated by damaged knitting needles and raise the alarm. We developed a knitting needle status monitoring setup using optical imaging, photoelectric detection and weak signal processing technology to achieve real-time monitoring of weaving needles’ position. Depending on the shape of the knitting needle, we designed a kind of Glass Optical Fiber (GOF) light guides with a rectangular port used for transmission of the signal light. To be able to capture the signal of knitting needles accurately, we adopt a optical 4F system which has better imaging quality and simple structure and there is a rectangle image on the focal plane after the system. When a knitting needle passes through position of the rectangle image, the reflected light from needle surface will back to the GOF light guides along the same optical system. According to the intensity of signals, the computer control unit distinguish that the knitting needle is broken or curving. The experimental results show that this system can accurately detect the broken needles and the curving needles on the knitting machine in operating condition.
Design and development of multiwavelength Mie-Polarization-Raman aerosol lidar system
Show abstract
Atmospheric aerosols play a major role in many atmospheric processes concerning the earth’s radiation budget, air quality, clouds and percipitation, and atmospheric chemistry. A multiwavelength Mie-Polarization-Raman lidar system is developing at Shandong Academy of Sciences Institute of Oceanorgraphic Instrumentation (SDIOI), which is used for the profiling of optical and physical aerosol properties. This system is specifically designed for characterizing marine aerosol which consists of a complex mix of different aerosol types. The aerosol lidar consists of a tripled Nd:YAG laser with three wavelengths, 30 cm telescope, six receiver channels and data acquistion subsystem. It provides particle backscatter coefficients at 355, 532 and 1064 nm (3β), extinction coefficients at 355 and 532 nm (2α), and depolarization ratio (σ). There are two Raman channels to collect the Raman signals backscattered by nitrogen molecules at 607 nm and by water vapor moecules at 407 nm. In this paper, we mainly describe the details of the optical setup, structure and performance of the lidar system. At last, the simulated signals based on the specifications are presented to demonstrate the capabilities of the lidar system.
The research of Raman spectra measurement system based on tiled-grating monochromator
Show abstract
A set of Raman spectrum measurement system, essentially a Raman spectrometer, has been independently designed and accomplished by our research group. This system adopts tiled-grating structure, namely two 50mm × 50mm holographic gratings are tiled to form a big spectral grating. It not only improves the resolution but also reduces the cost. This article outlines the Raman spectroscopy system’s composition structure and performance parameters. Then corresponding resolutions of the instrument under different criterions are deduced through experiments and data fitting. The result shows that the system’s minimum resolution is up to 0.02nm, equivalent to 0.5cm-1 wavenumber under Rayleigh criterion; and it will be up to 0.007nm, equivalent to 0.19cm-1 wavenumber under Sparrow criterion. Then Raman spectra of CCl4 and alcohol have been obtained by the spectrometer, which agreed with the standard spectrum respectively very well. Finally, we measured the spectra of the alcohol solutions with different concentrations and extracted the intensity of characteristic peaks from smoothed spectra. Linear fitting between intensity of characteristic peaks and alcohol solution concentrations has been made. And the linear correlation coefficient is 0.96.
Study on the extinction coefficient of spherical aerosol particles
Show abstract
Based on Mie scattering theory, this paper introduces the basic principle of aerosol light scattering and the basic calculation method of the polarization characteristics of scattering light. The spherical aerosol model is widely applied for the convenient and simple theoretic calculation, using the scattering theory by introducing the scattering amplitude matrix to combine incident radiation with scattering light. In scattering theory, aerosol extinction parameter has very important role for improving the precision of the laser radar, remote sensing detection and so on. We have mainly discussed the relationship between the spherical particle radius and extinction coefficient, and relationship between refractive index of the particles and extinction coefficient, respectively. It is concluded that extinction coefficient as a function of particles’ radius gradually oscillate approaching to 2 with the increasing of particle radius, and extinction coefficient curves as a function of refraction index have completely symmetric. The first major maximum of extinction coefficient also has obvious changes with different particles radius or refractive index.
The double grating monochromator’s design for pure rotational Raman lidar
Show abstract
The pure rotational Raman lidar temperature measurement system is usually used for retrieval of atmospheric temperature according to the echo signal ratio of high and low-level quantum numbers of N2 molecules which are consistent with the exponential relationship. An effective method to detect the rotational Raman spectrum is taking a double grating monochromator. In this paper the detection principle and the structure of the dual-grating monochromator are described, with analysis of rotational Raman’s Stokes and anti-Stokes spectrums of N2 molecule, the high order and lower order quantum number of the probe spectrum are resolved, then the specific design parameters are presented. Subsequently spectral effect is simulated with Zemax software. The simulation result indicates that under the condition of the probe laser wavelength of 532nm and using double-grating spectrometer which is comprised by two blazed gratings, Raman spectrums of 529.05nm, 530.40nm, 533.77nm, 535.13nm can be separated well, and double-grating monochromator has high diffraction efficiency.
High-speed signal sampling technique in lidar application
Yong Zhang,
Yuan Zhao,
Feng Liu,
et al.
Show abstract
Common lidar systems sets the standard using only one sample data from the laser echo signal, while
information from signal waveform is ignored, constraining further enhancement of range resolution and
accuracy. By employing high-speed signal sampling technique, we make full use of the echo signal, and
achieved large improvement on range resolution and accuracy. Moreover, the digital signal processing algorithm
can be adopted for different targets, which provides better versatility of the lidar system. This paper reviewed
high speed signal sampling technique and its application in lidar system. The HT high-speed DAQ developed in
our group was used in both FMCW lidar and pulse laser radar. Over fourfold increase in range accuracy,
comparing to that of traditional method, is demonstrated.
Recognition of edible oil by using BP neural network and laser induced fluorescence spectrum
Show abstract
In order to accomplish recognition of the different edible oil we set up a laser induced fluorescence spectrum system in the laboratory based on Laser induced fluorescence spectrum technology, and then collect the fluorescence spectrum of different edible oil by using that system. Based on this, we set up a fluorescence spectrum database of different cooking oil. It is clear that there are three main peak position of different edible oil from fluorescence spectrum chart. Although the peak positions of all cooking oil were almost the same, the relative intensity of different edible oils was totally different. So it could easily accomplish that oil recognition could take advantage of the difference of relative intensity. Feature invariants were extracted from the spectrum data, which were chosen from the fluorescence spectrum database randomly, before distinguishing different cooking oil. Then back propagation (BP) neural network was established and trained by the chosen data from the spectrum database. On that basis real experiment data was identified by BP neural network. It was found that the overall recognition rate could reach as high as 83.2%. Experiments showed that the laser induced fluorescence spectrum of different cooking oil was very different from each other, which could be used to accomplish the oil recognition. Laser induced fluorescence spectrum technology, combined BP neural network，was fast, high sensitivity, non-contact, and high recognition rate. It could become a new technique to accomplish the edible oil recognition and quality detection.
A beam parallelism testing method for multi-wavelength integrated collimating laser source
Wei-ming Wang,
Zhi-bin Chen,
Ming-xi Xue
Show abstract
The multi-wavelength integrated collimating laser source is the essential component of the receiving systems’
performance testing for various laser devices, by which the semiconductor laser chips with four typical peak wavelengths
are bonded to the surface of the metal carrier. While because the structure of the four lasers are not of coaxial, thus their
beam parallelism via the collimating optical system is a key index needed to be tested after the manufacturing process.
A testing method based on the image acquisition and processing of the laser spots was proposed in this paper, which
effectively solved the correction problem of the beam parallelism testing after the laser source was carried out. Firstly,
the laser source and the collimator which internally installed a laser spot collector on its focus panel were aligned, and
the laser spot from each semiconductor lasers was collected respectively; Secondly, the spot images were de-noised with
the PDE (Partial Differential Equation) algorithm and each spot centroid was obtained sequentially. Finally the
parallelism index of the multi-wavelength laser beams was gotten by the comparisons of the spot centroids. This method
is of high testing accuracy and good versatility, and easy to operate, thus it has a wide application prospect.
Phase compensation of SAL imaging combining Rayleigh LGS with PGA in strong turbulence
Show abstract
High imaging resolution can be achieved by using synthetic aperture ladar (SAL) with laser radiation source. The
destruction of the signal phase information caused by atmospheric turbulence makes the optical heterodyne detection
efficiency reduce. Therefore the imaging performance of SAL degraded seriously. The study on the influence of
atmospheric turbulence on SAL imaging is of great significance and an effective compensation method of image is
necessary to be found. Research shows that conventional phase gradient autofocus (PGA) algorithm has some
improvement on SAL imaging only in weak turbulence. The mixed phase compensation method combining Rayleigh
laser guide star (LGS) with PGA algorithm is presented based on the real-time detection of optical wavefront phase
distortion with Rayleigh LGS and the phase compensation method of the SAL images. The phase distortion caused by
different turbulence intensities with von Karman spectrum is estimated with Rayleigh LGS. SAL echo signals are
compensated with the estimated phase and the PGA algorithm is implemented in the final imaging data. The results show
that significant improvements of the SAL images in moderate turbulence are obtained and the images can be identified
basically by using the mixed phase compensation method in strong turbulence. The focusing effect of the SAL images is
improved effectively, and a higher SAL resolution is gained in azimuth. In addition, the research of SAL imaging
compensation in atmospheric turbulence in a slant path is carried out for the first time, which is of great significance to
the practical application of SAL.
A low-power CMOS trans-impedance amplifier for FM/cw ladar imaging system
Show abstract
A scannerless ladar imaging system based on a unique frequency modulation/continuous wave (FM/cw) technique
is able to entirely capture the target environment, using a focal plane array to construct a 3D picture of the target. This
paper presents a low power trans-impedance amplifier (TIA) designed and implemented by 0.18 μm CMOS technology,
which is used in the FM/cw imaging ladar with a 64×64 metal-semiconductor-metal(MSM) self-mixing detector array.
The input stage of the operational amplifier (op amp) in TIA is realized with folded cascade structure to achieve large
open loop gain and low offset. The simulation and test results of TIA with MSM detectors indicate that the single-end
trans-impedance gain is beyond 100 kΩ, and the -3 dB bandwidth of Op Amp is beyond 60 MHz. The input common
mode voltage ranges from 0.2 V to 1.5 V, and the power dissipation is reduced to 1.8 mW with a supply voltage of 3.3 V.
The performance test results show that the TIA is a candidate for preamplifier of the read-out integrated circuit (ROIC)
in the FM/cw scannerless ladar imaging system.
A fast spin images matching method for 3D object recognition
Show abstract
Spin image has been applied to 3D object recognition system successfully because of its advantages of rotation,
translation and view invariant. However, this method is very time consuming, owning to its high-dimensional
characteristics and its complicated matching procedure. To reduce the recognition time, in this paper we propose a
coarse-to-fine matching strategy for spin images. There are two steps to follow. Firstly, a low dimensional feature is
introduced for a given point. The feature contain two components, its first component is the perpendicular distance from
the centroid of the given point’s neighbor region to the tangential plane of the given point, its second component is the
maximum distance between the projection point of the centroid on the tangential plane and projection points of the
neighbor region on the tangential plane. Secondly when comparing a point from a target with a point from a model, their
low features are matched first, only if they satisfy the low feature constrains, can they be selected as a candidate point
pair and their spin images are further matched by similarity measurement. When all the target points and all the model
points finish above matching process, those candidate point pairs with high spin image similarity are selected as
corresponding point pairs, and the target can be recognized as the model with the most amount of corresponding point
pairs. Experiment based on Stanford 3D models is conducted, and the comparison of experiment results of our method
with the standard spin image shows that the propose method is more efficient while still maintain the standard spin
image’s advantages.
Low-noise preamplifier based on PMT and its signal processing
Show abstract
Through the establishment of the noise model for photomultiplier, estimate the signal-to-noise ratio of
the photomultiplier tube, using the principle of photoelectric detection technology, combined with the
needs of practical applications; select the appropriate photoelectric multiplier tube, from the two
aspects of the dynamic design and static design to ensure the correct output signal of the
photomultiplier tube. The low noise preamplifier will amplify the output signal of photomultiplier tube
without noise as soon as possible. This article describes the design principles of the photomultiplier
tube selection and application. From the op-amp selection, multistage amplifier circuit design, circuit
noise estimation, PCB board layout line and shielding, proposed a practical circuit design of 10MHz
band width; and matters needing attention and its signal processing method. The simulation results
show that the signal amplifying circuit designed, this circuit design can be very well amplifying and
processing the output signal of the photomultiplier tube. To verify the theory of articles derived from
circuit simulation to the actual test. Simulation results show that the signal amplifying circuit design,
this form of circuit design can be very good enlarged and processing the output signal of the
photomultiplier tube. From the actual test, the test results show that the accuracy and practicality of the
simulation results.
Developing a phase and intensity measurement technique with multiple incident angles under surface plasmon resonance condition
Show abstract
This work presents the application of a focused beam polarizer-sample-analyzer imaging ellipsometer in measuring the ellipsometric parameters under the surface plasmon resonance condition. By using a cylindrical lens to produce fan shaped beam with multiple incident angles, three-intensity measurement technique can measure the ellipsometric parameters against each incidence but without the need of calibrating the azimuth errors of polarizer and analyzer. As a result of multiple incident angles approach, the whole SPR curve can be obtained without rotating the sensor chip. The intensity and phase response in the air and water interface of the sensor chip were demonstrated, and almost all measured results are close to the theoretical model.
Monte Carlo simulation of laser beam scattering by water droplets
Biao Wang,
Guang-de Tong,
Jia-xuan Lin
Show abstract
Monte Carlo simulation of laser beam scattering in discrete water droplets is present and the temporal profile of LIDAR signal scattered from random distributed water droplets such as raindrop and fog is acquired. A photon source model is developed in the simulation for laser beam of arbitrary intensity distribution. Mie theory and geometrical optics approximation is used to calculate optical parameters, such as scattering coefficient, Aledo and average asymmetry factor, for water droplets of variable size with gamma distribution. The scattering angle is calculated using the probability distribution given by Henyey-Greenstein phase function. The model solving semi-infinite homogeneous media problem is capable of handling a variety of geometries and arbitrary spatio-temporal pulse profiles.
Application technology of micro pulse lidar
Show abstract
With the constant exploration to the atmosphere and the attention to the air quality of the
living environment, the applications of micro-pulse lidar are more and more important. Micro Pulse
Lidar can be used to observe the distribution of atmospheric aerosol and analyse structure, spatial and
temporal evolution of the aerosol. The paper gives the introduction about the reference of micro-pulse
lidar which is researched in the laboratory. Through the precision optical design, the blind area of
Micro Pulse Lidar can be less than 45m. The portable requirement in the structure is implemented. The
software function of micro-pulse lidar includes: extinction coefficiency monitoring, tracking the
pollution source, distinguish spherical particular (fog) from no-sphercial particular(ice or dust)，
simulating the Mass concentration, scanning date integrating with GIS, and so on. The average height
of the boundary layer measured by micro-pulse lidar. The relationship between the cloud height and
aerosol echo signal can be seen from the data received from micro-pulse lidar and the peak is at 6KM.
By acquiring corresponding visibility values from probing different heights, a conclusion can be drawn
that visibility and extinction coeffcient is inversely proportionate. Take a 24 hour day as a circle and
divide it into several time periods. An atmosphere evolution diagram of the backscattering of the height
of atmospheric boundary layer and the atmospheric aerosol particles can be derived according to the
difference in sun radiation. Information like structure and the evolution characteristics of atmospheric
boundary layer, cloud height, cloud cover structure, atmospheric visibility and space particles obtained
by the laser radar detection provides a basis for the establishment of the correct atmospheric model. At
the same time because lidar can monitor the emissions of industrial soot and detect the law of diffusion
of environmental pollutants of the sky over cities, it is of great significance to the environmental
monitoring of the atmosphere and atmospheric science research.
Optoelectronic measurement for parameters of high-speed flying objects based on laser screen and photodiode array
Show abstract
The impacting or penetrating power of high-speed flying object can be evaluated by its mass and velocity, so the velocity and the mass are two key parameters. Here we present an optoelectronic measurement method for parameters of high-speed flying objects based on parallel laser screen and photodiode array. The system consists of two thin laser screens with parallel each other and certain distance, orthogonal two dimensional photodiode arrays, data acquisition module, control module and data transmission processing module. When the object flies through the thin screen, the incident light of some photodiodes at the corresponding position is blocked and the output states of the corresponding photodiodes are changed. The flying position, which can be used to correct the distance error, velocity and the overall dimension of the object are determined by high-speed sampling and storing all the output states of photodiode array at any sampling moment when the object flying through the thin screens. We employed a line-shaped laser diode and a Fresnel lens with long-focal-length and aberration-free to generate parallel laser screen. The high-speed large-amount parallel data sampling module is comprised of four FPGA-based boards with built-in FIFO buffer memory, and the control module is constructed by one FPGA board and a FLASH memory. Functions simulation and experiment results of the FPGA-based data acquisition storage and the LabVIEW-based data processing indicate that the method and the design are feasible.
Large viewing field wavefront sensing by using a lightfield system
Show abstract
To overcome the shortcomings of Shack-Hartmann wavefront sensor, we developed a lightfield wavefront detection system,
which is able to complete the large field of view, multi-perspective wavefront detection in a single photographic exposure.
The lightfield wavefront detection system includes an imaging primary mirror, a lenslet array and a photosensitive device.
The lenslet array is located on the imaging plane of the imaging primary mirror and the photosensitive device is located on
the focal plane of the lenslet array. In this system, each lenslet reimages the aperture and forms a low-resolution image of
the aperture. Compared with the Shack-Hartmann sensor, this lightfield measuring method can obtain imaging arrays in
different perspectives. By comparing the array information with the standard information, we can obtain the slope matrix of
the wavefront in different perspectives and restore the wavefront in a large field of view. Based on Fourier optics, we built
the corresponding theoretical model and simulation system. By busing Meade telescope, turbulent phase screen, lenslet
array and CCD camera, we founded the experimental lightfield wavefront measuring system. Numerical simulation results
and experimental results show that this wavefront measuring method can effectively achieve the wavefront aberration
information. This wavefront measurement method can realize the multi-perspective wavefront measurement, which is
expected to solve the problem of large viewing field wavefront detection, and can be used for adaptive optics in giant
telescopes.
Development of a test facility for 3D laser imaging technology studies
Show abstract
A 3D laser imaging test facility was developed and established using a module design approach. The test facility
provides a complete, controllable and repeatable experiment environment, and supports research and simulation of 3Dimaging
LiDAR system. The test facility consists of five major parts: an open 3D-imaging LiDAR, a target simulator, a
far-field emulation, a background light environment simulation system, and a large FOV stereo vision system. The test
facility has been set three working modes: unit module analysis mode, accuracy and imaging mechanism of LiDAR
system mode, moving target detecting and environmental modeling mode. The open test facility continually evolves to
meet the expanding role of 3D laser imaging applications.
Recent development of 3D imaging laser sensor in Mitsubishi Electric Corporation
Show abstract
We have been developing 3-D imaging laser sensors for several years, because they can acquire the additional information of the scene, i.e. the range data. It enhances the potential to detect unwanted people and objects, the sensors can be utilized for applications such as safety control and security surveillance, and so forth. In this paper, we focus on two types of our sensors, which are high-frame-rate type and compact-type. To realize the high-frame-rate type system, we have developed two key devices: the linear array receiver which has 256 single InAlAs-APD detectors and the read-out IC (ROIC) array which is fabricated in SiGe-BiCMOS process, and they are connected electrically to each other. Each ROIC measures not only the intensity, but also the distance to the scene by high-speed analog signal processing. In addition, by scanning the mirror mechanically in perpendicular direction to the linear image receiver, we have realized the high speed operation, in which the frame rate is over 30 Hz and the number of pixels is 256 x 256. In the compact-type 3-D imaging laser sensor development, we have succeeded in downsizing the transmitter by scanning only the laser beam with a two-dimensional MEMS scanner. To obtain wide fieldof- view image, as well as the angle of the MEMS scanner, the receiving optical system and the large area receiver are needed. We have developed the large detecting area receiver that consists of 32 rectangular detectors, where the output signals of each detector are summed up. In this phase, our original circuit evaluates each signal level, removes the low-level signals, and sums them, in order to improve the signalto- noise ratio. In the following paper, we describe the system configurations and the recent experimental results of the two types of our 3-D imaging laser sensors.
Development of the ZJU polarized near-infrared high spectral resolution lidar
Show abstract
Quantitative measurements of atmospheric aerosol optical properties are required for studies of the Earth’s radiation
budget and climate change. Taking advantage of the broad spectrum of the Cabannes-Brillouin scattering from
atmospheric molecules, the high spectral resolution lidar (HSRL) technique employs a narrow spectral filter to reject the
aerosol Mie scattering component in the lidar return signals. Therefore, an HSRL can directly measure the extinction and backscatter coefficient as well as the lidar ratio. Since the backscattering signal is proportional to 1/λ4, it presents high requirements for the spectral filter to build a near-infrared HSRL. The atomic/molecular absorption filters are limited by the wavelength and it is also challenging for Fabry-Perot interferometers (FPI) due to their small field of view(FOV). The field-widened Michelson interferometer, which has a large FOV, is considered to be a good candidate for the spectral filter of near-infrared HSRL. A polarized near-infrared HSRL instrument, which employs a field-widened Michelson interferometer as the spectral filter, is under development at the Zhejiang University (ZJU), China. In this paper, the methodology and design process of the instrument will be described in detail. The capability of the HSRL in determining the properties of the atmosphere will be addressed. The retrieval of the aerosol optical properties, such as
extinction-to-backscatter ratio and aerosol depolarization ratio, will be presented. Sensitivity of the aerosol retrieval to
errors in characterizing the spectral filter will also be investigated.
Effect of transmitting beam position error on the imaging quality of a Fourier telescope
Show abstract
The effect of beam position error on the imaging quality of a Fourier telescope is analyzed in this paper. First, the origin of the transmitting beam position error and the error types are discussed. Second, a numerical analysis is performed. To focus on the transmitting beam position error, other noise sources exclusive of the reconstruction process are neglected. The Strehl ratio is set to be the objective function and the transfer function of the position error is constructed. Based on the numerical model, the features of Strehl ratio reduction caused by position error are deduced. Third, simulations are performed to study the position error effect on the imaging quality. A plot of the Strehl ratio versus the different levels of position errors is obtained and the simulation results validate the numerical model to a certain extent. According to the simulation results, a high value of the transmitting beam position error obviously degrades the imaging quality of the system; thus, it is essential to contain the position error within a relatively low level.
The error analysis and correcting of scale tape grating encoder
Show abstract
High precision pointing and tracking is an important performance indicator of the telescope, and tracking is implemented mainly by the azimuth axis and the altitude axis movement together method for alt-azimuth designed telescopes, and as a control feedback angle encoder must be installed on the azimuth axis, pitch axis. Scale tape grating encoder due to the advantages of non-contact measurement, high precision, simple assembly and adjustment, as a new generation of angle encoders has been widely used in modern telescopes’ angle measuring system. However performance of these systems can be limited by the factors of mechanical installation, machining error, random error, and other types of error, which often fail to meet arcsecond or sub-arcsecond angle measurement requirements. This paper analyzes the impacts of the mechanical installation eccentric, the roundness error, shafting sloshing on encoder angle measuring, and develops a 4 reading heads, which have 90 ° phase difference, software subdivision angle measurement program. And we make counterclockwise and clockwise angle measuring experiments on a experimental platform, which has mechanical installation eccentric 10um, roundness error 2um and shafting sloshing 0.6". Two sets of experiments measuring angle error RMS values are 0.387'' and 0.487''. The experiments prove that the program can eliminate the angular measurement error due to the mechanical installation the eccentric, machining roundness error, shafting sloshing, achieve arcsecond angle measuring.
A method of infrared small targets detection based on local third order moment
Gui-hua Fan,
Ting-hua Zhang,
Jian-guo Zhu,
et al.
Show abstract
Restrain background clutter in infrared image is the first step before detecting and tracking. As infrared sensor is easily affected by atmosphere hot radiation, long distance and sensor noise, the detected targets in infrared images often present like small targets and drowned in noise. So it’s difficulty to detect the small target in complex background, especially doing it with single frame. A new method of infrared small targets detection based on local third order moment is proposed. Firstly, the local third order moment of target and background are analyzed. The result is that the third order moment of target and background has distinctively difference in value. The local third order moment of background tends toward zero or less than zero, while that of target is greater than one. Secondly, the global normalization is carried out after the third order moment operation to single frame image. With this algorithm, the background magnitude is almost near zero, and the potential targets magnitude is near to one. So the background clutter in the infrared images is suppressed effectively. And the target can be detected with fixed threshold. At last, false target judgment criterion is used, which can eliminate remained big bright object boundary effectively. The experiment results proved that this arithmetic has robust performance to restrain different background clutter; even in the situation the background clutter have high grey-level than the small target.
Effect analysis of nonuniformity on four-quadrant detector and compensation correction
Show abstract
The four-quadrant detector is mainly used for high-precision position measurement and related fields, and the
requirement of accuracy keeps increasing. The effection of photoresponse nonuniformity on measurement accuracy of
four-quadrant detector is analyzed theoretically in this paper. The correction method is proposed through calculation,
simulation and analysis. Finally, the experimental platform is built to verify. The results of experiments demonstrate that
after compensated correction, the nonuniformity of detector has been 46.17% compensated, the nonlinear deviation has
been decreased by 44.1%, the measurement accuracy of spot displacement has been improved by 1.33 times.
Design and analysis of displacement measurement system based on the four-quadrant detector
Show abstract
The four-quadrant detector is mainly used in high-precision displacement measurement and other related fields. With the emergence of displacement problem in a large number of projects, the displacement measurement accuracy, speed and reliability have become increasingly demanding. In this paper, the measurement principle of four-quadrant detector is analyzed theoretically, the displacement measurement system based on four-quadrant detector is designed, and the experimental platform is built to test and validate the stability, measurement accuracy and range of the displacement measurement system. Experimental results show that: the deviation of the same spot position on measurement system is less than 0.17μm. The measurement error of spot displacement is less than 3.7μm.
A UGV-based laser scanner system for measuring tree geometric characteristics
Yonghui Wang,
Yubin Lan,
Yongjun Zheng,
et al.
Show abstract
This paper introduces a laser scanner based measurement system for measuring crop/tree geometric characteristics. The measurement system, which is mounted on a Unmanned Ground Vehicle (UGV), contains a SICK LMS511 PRO laser scanner, a GPS, and a computer. The LMS511 PRO scans objects within distance up to 80 meters with a scanning frequency of 25 up to 100Hz and with an angular resolution of 0.1667° up to 1°. With an Ethernet connection, this scanner can output the measured values in real time. The UGV is a WIFI based remotely controlled agricultural robotics system. During field tests, the laser scanner was mounted on the UGV vertically to scan crops or trees. The UGV moved along the row direction with certain average travel speed. The experimental results show that the UGV's travel speed significantly affects the measurement accuracy. A slower speed produces more accurate measuring results. With the developed measurement system, crop/tree canopy height, width, and volume can be accurately measured in a real-time manner. With a higher spatial resolution, the original data set may even provide useful information in predicting crop/tree growth and productivity. In summary, the UGV based measurement system developed in this research can measure the crop/tree geometric characteristics with good accuracy and will work as a step stone for our future UGV based intelligent agriculture system, which will include variable rate spray and crop/tree growth and productivity prediction through analyzing the measured results of the laser scanner system.
LED mini-lidar for air and dust monitoring
Show abstract
LED mini-lidar is a new concept optical sensor, not to be replaced from the traditional lidar with
laser light source. To use this lidar in near range, several lidar parameters were rearranged due to
the new concept. LED device is tough against rough treatment. It has wide color variation
including NUV and NIR regions. Its beam is hard to collimate because of LED lamp size, while its
power is estimated to be enough to monitor the atmosphere and dusts for a few hundred meters.
LED mini-lidar has a high repetition frequency of more than 100kHz to accumulate weak lidar
echoes. The original photon counter was designed to follow the high repetition frequency. The
several types of LED lidars were developed to monitor air motion and dust flow.
Three radar imaging methods based on the one-dimensional laser range profile
Show abstract
One-dimensional range profile is known as a simple radar imaging technology. Based on the imaging mechanism, the laser range profiles (LRPS) of the convex rotators in three different methods, which named as the Beam Scattering Method (BS method), Radar Cross Section Method (RCS method) and Surface Elements Method (SE method),were studied. In detail, BS method, which combined the laser beam pulse scattering theory and radar equation, is the very model that can be applied to the convex quadric rotary bodies, however, it may produce singular solutions in certain incident directions. The RCS method is just an extension of the theory of radar cross section theory and radar equation. According to the definition, the simplest forms of RCS which were then substituted into the radar equation were obtained, finally the one-dimensional range profiles were analytically resolved. The SE Method is a much more comprehensive theory to get the laser range profiles of arbitrary objects. The object should be first divided into numerous small triangle facets, and sum the backscattering power of these facets in the same distance, and in this way the final LRPS were deduced. In the meanwhile, the SE method is the most convenient way to evolve into the three-dimensional range profile. In the paper, the LRPS of a cone based on the three models above were simulated, it was found that the features and shape of each profiles were similar basically, but theoretical correction to SE method was still needed.
The research on calibration methods of dual-CCD laser three-dimensional human face scanning system
Show abstract
In this paper, on the basis of considering the performance advantages of two-step method, we combines the stereo matching of binocular stereo vision with active laser scanning to calibrate the system. Above all, we select a reference camera coordinate system as the world coordinate system and unity the coordinates of two CCD cameras. And then obtain the new perspective projection matrix (PPM) of each camera after the epipolar rectification. By those, the corresponding epipolar equation of two cameras can be defined. So by utilizing the trigonometric parallax method, we can measure the space point position after distortion correction and achieve stereo matching calibration between two image points. Experiments verify that this method can improve accuracy and system stability is guaranteed. The stereo matching calibration has a simple process with low-cost, and simplifies regular maintenance work. It can acquire 3D coordinates only by planar checkerboard calibration without the need of designing specific standard target or using electronic theodolite. It is found that during the experiment two-step calibration error and lens distortion lead to the stratification of point cloud data. The proposed calibration method which combining active line laser scanning and binocular stereo vision has the both advantages of them. It has more flexible applicability. Theory analysis and experiment shows the method is reasonable.