Proceedings Volume 6622

International Symposium on Photoelectronic Detection and Imaging 2007: Laser, Ultraviolet, and Terahertz Technology

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Proceedings Volume 6622

International Symposium on Photoelectronic Detection and Imaging 2007: Laser, Ultraviolet, and Terahertz Technology

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Volume Details

Date Published: 7 March 2008
Contents: 2 Sessions, 81 Papers, 0 Presentations
Conference: International Symposium on Photoelectronic Detection and Imaging: Technology and Applications 2007 2007
Volume Number: 6622

Table of Contents

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Table of Contents

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  • Front Matter: Volume 6622
  • Laser, Ultraviolet, and Terahertz Technology
Front Matter: Volume 6622
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Front Matter: Volume 6622
This PDF file contains the front matter associated with SPIE Proceedings Volume 6622, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.
Laser, Ultraviolet, and Terahertz Technology
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Color (RGB) imaging laser radar
M. Ferri De Collibus, L. Bartolini, G. Fornetti, et al.
We present a new color (RGB) imaging 3D laser scanner prototype recently developed in ENEA (Italy). The sensor is based on AM range finding technique and uses three distinct beams (650nm, 532nm and 450nm respectively) in monostatic configuration. During a scan the laser beams are simultaneously swept over the target, yielding range and three separated channels (R, G and B) of reflectance information for each sampled point. This information, organized in range and reflectance images, is then elaborated to produce very high definition color pictures and faithful, natively colored 3D models. Notable characteristics of the system are the absence of shadows in the acquired reflectance images - due to the system's monostatic setup and intrinsic self-illumination capability - and high noise rejection, achieved by using a narrow field of view and interferential filters. The system is also very accurate in range determination (accuracy better than 10-4) at distances up to several meters. These unprecedented features make the system particularly suited to applications in the domain of cultural heritage preservation, where it could be used by conservators for examining in detail the status of degradation of frescoed walls, monuments and paintings, even at several meters of distance and in hardly accessible locations. After providing some theoretical background, we describe the general architecture and operation modes of the color 3D laser scanner, by reporting and discussing first experimental results and comparing high-definition color images produced by the instrument with photographs of the same subjects taken with a Nikon D70 digital camera.
Study on applications of terahertz technology
Ji-jun Luo, Su-xia Hou, Jun Xu, et al.
Terahertz (THz) technology, as new research topic and technology field which is paid more and more attention by the researchers and governments, has some unique properties which is different from other electromagnetic wave. THz wave is regarded to have potential application in many fields. Existing and emerging applications of terahertz technology in imaging, medicine, biology, space exploration, covert communications, compact radar ranges, industrial controls, terahertz microscopy, terahertz tomography, and homeland security have stimulated intensive research effort in photonics and electronics technologies bracketing the famous terahertz gap from the high and low frequency sides, respectively. Cutoff frequencies and maximum frequencies of operation of InGaAs-based Heterostructure Bipolar Transistors and High Electron Mobility Transistors are now approaching or even exceeding 600 GHz. New ideas of using plasma resonances of two-dimensional electrons for tunable detection and emission of terahertz radiation are being explored and proven experimentally. Plasma effects in polarization-induced electrons and holes in granular pyroelectric/semiconductor heterostructures hold promise of an active THz medium tunable by external electric field or light.
Influence of beam incidence angle on laser cleaning of surface particles
Su-xia Hou, Ji-jun Luo, Qing-hua Zhang, et al.
Laser cleaning technology has great advantages. The influence of beam incidence angle was studied in the case of the removal weakly absorbing particles on absorbing particles on absorbing Si wafers by 248 nm DUV light pulse. By decreasing the beam incidence angle from 80° to 10°, the removal efficiency of 0.15-0.30 µm Si3N4 particles was increased by 30-45%, while no improvement was observed with 0.3 μm SiO2 particles. Theoretical calculations show that decreasing the incidence angle from 80° to 10° results in a 30-fold increase of the horizontal component of the radiation pressure force, whereas the vertical component remains unchanged as the beam width must be decreased to keep a constant fluence at the workpiece. This force would help removing particles by making them roll. Based on theoretical calculations, it is proposed that the enhanced removal of particles at grazing incidence is caused by the horizontal component of the beam radiation pressure. The difference between Si3N4 and SiO2 particles is attributed to the influence of particle shape on van der Waals adhesion forces: the adhesion force of irregularly shaped Si3N4 particles would be comparable to the horizontal component of the radiation pressure force, whereas the adhesion force of spherical SiO2 particles would be higher.
Optical characteristics of dielectric barrier uniform discharge at atmospheric pressure
Xuechen Li, Pengying Jia, Zhihui Liu, et al.
Dielectric barrier uniform discharges have attracted considerable interest because this type of discharge requires practically no vacuum devices and plasma with good uniformity can be generated at high pressure. In this paper, discharges are initiated in air at atmospheric pressure in a dielectric barrier discharge setup composed of two parallel planar electrodes separated by two layers of dielectric. The characteristics of dielectric barrier discharge are studied through collecting the emission signals from the discharge with a photomultiplier tube and a spectrometer, respectively. The results show that the discharge consists of many micro-discharge filaments when the applied voltage is slightly above the breakdown voltage, and the discharge is uniform when the applied voltage is very high. The waveform of discharge emission consists of many pulses with duration of several tens nanoseconds in the filamentary discharge mode. However, it only consists of a single broad electrical pulse (hump) lasting approximately a quarter of a discharge time period on which significant narrow pulse peaks are superposed. Streamer breakdown mechanism is involved in the discharge of not only filamentary discharge but also uniform discharge. Spectral emission spectroscopy is used to study the discharge transition. The intensity ratio of 391.4nm to 337.1nm represents electron energy that is mainly determined by the electric filed applied to the gas gap. With increasing the applied voltage, the intensity ratio of 391.4nm to 337.1nm decreases. This experimental result indicates that electron energy decreases with the increasing of the applied voltage.
Evaluation of smokescreen jamming effect on electro-optical imaging systems
Wei Gao, Yan-ling Wei
Methods for quantitatively evaluating smokescreen jamming effect on electro-optical imaging systems are investigated. Smokescreen jamming could degrade the target discrimination ability of imaging systems. Based on the theory of digital image processing and the Johnson criterion for target detection and discrimination, which describes the quantitative relationship between the resolving power and target discrimination ability of imaging systems, four rules for quantitatively evaluating smokescreen jamming effect on imaging systems are proposed as the target-discrimination-grade rule, target-discrimination-probability rule, target-discrimination-range rule and correlativity rule. For the target-discrimination-grade rule, the smokescreen jamming effect is evaluated according to the change of target discrimination grade of the imaging system after being jammed. For the target-discrimination-probability rule, the jamming effect is evaluated according to the ratio of the discrimination probabilities of the imaging system before and after being jammed. For the target-discrimination-range rule, the jamming effect is evaluated according to the ratio of the discrimination ranges before and after being jammed, or the decline rate of discrimination range of the imaging system after being jammed. For the correlativity rule, the jamming effect is evaluated and graded as three jamming levels according to the correlativity between the images of the imaging system before and after being jammed, which could be expressed with the mean absolute difference or correlation function between the images before and after being jammed. Compared with the existing evaluation methods for the jamming effect on electro-optical imaging systems, the evaluation rules given here are featured as more quantitative, objective and readily applicable.
Scannerless imaging lidar detection techniques based on different systems
Huimin Chen, Jiantao Wang, Ping Li, et al.
With the development of the laser and radar technology, imaging lidar has been widely used in the fields of military applications. Without the scanner devices, scannerless imaging lidars have the characteristic of high frame rate, wide field of view and high reliability. Three kinds of scannerless imaging lidar system, such as based on the phase scannerless imaging lidar, based on the multiple-slit streak tube imaging lidar and based on the flash lidar have been analyzed in this paper. Moreover, the principle, the characteristics and limitations were investigated. Valuable conclusions were proposed for the selection of scannerless imaging lidar in certain circumstance.
Study on the techniques of pulse laser fuze
Huimin Chen, Xiaopeng Yan, Yi Ma, et al.
With the development of semiconductor laser technology, laser proximity fuzes have been widely used in various kinds of guided missiles and routine ammunitions. Combined with the current situation, the digital laser fuzes system based on the FPGA has been proposed in this paper. Combined with the current situation, the system has been divided into emitting module, receiving module and signal processing module, the three modules have been analyzed in details. In the emitting module, the driven circuit based on the FPGA has been developed, the laser pulse with 20ns width and 10kHz repetition frequency have been obtained. Meanwhile, the emitting optical system and receiving optical system have been designed. In the receiving module, the receiving circuit with preamplifier and A/D sampling and convert circuit have been developed. In the signal processing module, anti-interference methods were proposed which can find applications in the laser proximity fuze research.
Dynamics of pattern formation in dielectric barrier discharge with transparent electrodes
Lifang Dong, Xuechen Li, Pengying Jia
Spatio-temporal patterns in nonlinear system have been paid much attention in resent years. Among different nonlinear systems, gas discharge system is more remarkable because proper time scale and abundance in pattern structures. In this article, pattern formation dynamics is studied in a dielectric barrier discharge system with mixed working gas of argon and air at pressure of 0.6 atm by optical method. A boundary condition of square structure is used in the experiments. The experimental results show that the discharge pattern with increasing the applied voltage undergoes a scenario: uniform discharge, hexagon structure, stochastic micro-discharge filaments, hexagon structure again, square pattern, regular stripes that bridge the boundary, and uniform discharge again. The emission signals from the discharge in different pattern are detected by photomultiplier tubes and results show that the waveform of total light signals under low voltage lower than the voltage of stochastic micro-discharge filaments is only one pulse at each half cycle of the applied voltage, while it shows two pulses at each half cycle of the applied voltage in the second hexagon pattern and square pattern, and more pulses appear in the stripe pattern discharge and second uniform discharge. Through analyzing the temporal sequence of the different filaments in a hexagon, it can be concluded that the hexagon pattern is an interleaving of two rectangular sub-patterns that the micro-discharge filaments in a sub-pattern volley almost at the same time. The temporal sequence of the two sub-patterns in consecutive half cycle alternates.
Numerical simulation of polarized bidirectional reflectance distribution function (BRDF) based on micro-facet model
Weiwei Feng, Qingnong Wei, Shimei Wang, et al.
The polarized light scattered by the surface of a material contains information that can be used to describe the properties of the surface. Polarized Bidirectional Reflectance Distribution Function (BRDF) is one of the most important factors used to represent the property of the surface. It uses a 4×4 matrix (Mueller matrix) to describe the properties of the light scattered from the surface. A polarized BRDF model based on the micro-facet theory is used in the numerical simulation. The optical constant parameters contained in the model is derived from the experimental data through genetic algorithm. Comparison between the model calculation and the experimental data shows that this model agrees well with the experimental data, and can be used in the future work.
Progress on the optical spot preservation technique
Ding yu Liu, Ji lin Gu, Jia shi Sun
It is well-known that in a hyperbola can not give two identical optical spot having the same radius except symmetrical part. It has collimating method to decrease the divergent angle for the laser propagation, but the divergent angle cannot be reached zero [1]. So some opinions regarded that optical spot preservation can not be realized in the transmission of laser beam. We have suggested a method called double-lens method used for promoting the solution of such problem [2]. However, the physical pattern used to be not very clear such as the adaptive limits; whether or not the size of the optical spot can be arbitrarily taken; the law of the optical spot preservation versus double-lens distances etc. Since only one hyperbola can not be realized the optical-spot preservation, let's consider more than one hyperbola that encounter in space with different parameters, so it is possible to find out that there are some optical spots with the same size located at different position along the transmission line and the connection of them will be achieved a continuous flow corresponding to the propagation of the laser wave. According to this analysis, a laser beam with the certain radius can be emitted to the artificial satellite, even back and forth; the size of the optical spot remains a constant. In this paper, I positively say the optical spot preservation can be not only proved by mathematical derivation but realized by practice in the laboratory. [3] It will be applied to collision avoidance [4].
Fiber Bragg grating sensor for the simultaneous measurement of stress and temperature in high temperature environment
Fang Li, Yuesong Jiang
A novel fiber Bragg grating sensor operating in the environment of high temperature is studied. And the sensor can realize the simultaneous measurement of stress and temperature. The sensing head is comprised of one metal strip, one adiabatic strip and two FBGs with the same specification. The metal strip converts the measured temperature into the strain of the FBG2, and the temperature will be related to the peak wavelength shift of the FBG2 induced by the strain. The sensed stress in the environment of high temperature is transferred into the longitudinal strain applied into the FBG1 and FBG2 through the adiabatic strip and the metal strip, respectively, which will induced the peak wavelength shifts of the two fiber Bragg gratings. In this way, we can know the stress according to the center-wavelength shift of the FBG1, and the temperature from the difference of the peak wavelength between the FBG1 and FBG2. Finally, by a simple simulation we proved the physics feasibility of the sensor and found the fiber Bragg grating sensor has a stress sensitivity of about 0.15pm per N, and a temperature sensitivity of about 4pm per °C. A temperature dynamic range of 900°C can be obtained.
A near infrared optimal wavelength imaging method for detection of foreign materials
De-Hao Lu
The objective of this research was to develop an optimal wavelength imaging system for detecting foreign materials in the NIR (near infrared) region from 750 nm to 2500 nm. This method is based on the principle that different fibers have different spectral absorptions and reflectance characteristic. When submitted to a source of illumination at different wavelength, foreign materials present different reflectance values in comparison to those from cotton fibers. For simultaneously discriminating several types of foreign materials from cotton, the optimal wavelength evaluation function for describing the cotton/foreign materials absorption discrimination was set up. Through the Fourier transform spectrometer experiment, the optimal wavelength for these detected foreign materials was determined and accordingly an optimal wavelength imaging system was developed. The wavelength selection experiment showed that the 940 nm wavelength was the most appropriate for detection of a wide range of foreign materials in cotton, and the 940 nm wavelength imaging system gave the clear image features of these foreign materials. The result suggests that use of NIR optimal wavelength imaging technique is a feasible and effective method to detect foreign materials in cotton, which are currently difficult for sorting.
Semi-physical simulation test for micro CMOS star sensor
Jian Yang, Guang-jun Zhang, Jie Jiang, et al.
A designed star sensor must be extensively tested before launching. Testing star sensor requires complicated process with much time and resources input. Even observing sky on the ground is a challenging and time-consuming job, requiring complicated and expensive equipments, suitable time and location, and prone to be interfered by weather. And moreover, not all stars distributed on the sky can be observed by this testing method. Semi-physical simulation in laboratory reduces the testing cost and helps to debug, analyze and evaluate the star sensor system while developing the model. The test system is composed of optical platform, star field simulator, star field simulator computer, star sensor and the central data processing computer. The test system simulates the starlight with high accuracy and good parallelism, and creates static or dynamic image in FOV (Field of View). The conditions of the test are close to observing real sky. With this system, the test of a micro star tracker designed by Beijing University of Aeronautics and Astronautics has been performed successfully. Some indices including full-sky autonomous star identification time, attitude update frequency and attitude precision etc. meet design requirement of the star sensor. Error source of the testing system is also analyzed. It is concluded that the testing system is cost-saving, efficient, and contributes to optimizing the embed arithmetic, shortening the development cycle and improving engineering design processes.
Study on chromaticity balance for LED exposure system
Cheng-bao Yao, Shu-ying Wang, Xian-wei Rong, et al.
A standard white light compounding algorithm based on combination of CCD illumination acquisition with computer control is presented for LEDs. The computer adjust and control the working current of LEDs by using three-color LEDs illumination acquired by CCD camera, achieved chromaticity coordinates error between compounded white light and standard white light D65 less than the threshold beforehand setted by this technique, then acquiring needed standard white light. Compounded white light meet the chromaticity error demand that is able to be changed, at the same time the CCD illumination acquisition system is eliminated. The proposed algorithm improved the light energy utilization efficiency of LED, and eliminated the offset of central wavelength and chromaticity coordinates due to work current change of LEDs. Experimental results show that the proposed algorithm achieved lesser chromaticity error uv=0.001 relative to standard white light D65, enhanced chromaticity uniformity of illumination field.
Analysis of vibrational temperature of patterns in two-gas-species discharge by using photoelectronic detection systems
Lichun Li, Lifang Dong, Yanzhao Zhang, et al.
The non-intrusive optical emission spectroscopy of the N2 second positive band system (C3Πu→B3Πg) are used to measure the vibrational temperature in N2/Ar and air/Ar discharges at atmospheric pressure, respectively. In N2/Ar discharges, the strip patterns can be obtained at the concentration of N2 from 9.5% to 38% at 10kV and 60kHz, and its vibrational temperature increases approximately from 1600K to 1750K with increasing the N2 concentration. Increasing the concentration of N2 from 38% to 96%, the hexagon patterns are formed and its vibrational temperature increases from 1750K to 1950K. In air/Ar discharges, three patterns (strips, quasisuperlattice and hexagon) are obtained with air concentration increasing from 9.5% to 96% at 10kV and 60kHz. The vibrational temperature ranges approximately from 1850K to 2750K, which is about 250~600K higher than that in N2/Ar discharges under the same concentration of N2 and air in two-gas-species. In addition, the quasisuperlattice can be observed at the air concentration from 19% to38%, and its vibrational temperature is from 2000K to 2300K approximately. It indicates that the gas species and the mixing ratios affect the patterns and their vibrational temperatures. Furthermore, it is also found that the breakdown voltage and the moment of discharge initiation are different as a function of the gas species and the mixing ratios.
Study of channel character of solar blind UV communication
Yi Tang, Guo-qiang Ni, Li-jun Zhang, et al.
The definition and classifications of the UV communication are described in the paper. The UV channel consists of three sections: propagation loss section, scattering section and background-noise section. The principle of selecting the wave band of UV communication is analyzed. The LOS and NLOS (a) transmission models are presented, and the two configurations are well proved by outdoor experiments. The experiment results also show that the communication distance of LOS can go up to 5kms, and NLOS(a) can reach 2kms with the UV detectors at present.
Hyperspectral laser-induced flourescence imaging for assessing internal quality of kiwi fruit
Muhua Liu, Yifeng Liao, Xiaomei Zhou
This paper describes an experimental study on non-destructive methods for predicting quality of kiwifruits using fluorescence imaging. The method is based on hyperspectral laser-induced fluorescence imaging in the region between 700 and 1110 nm, and estimates the kiwifruits quality in terms of internal sugar content and firmness. A station for acquiring hyperspectral laser-induced fluorescence imaging has been designed and carefully choosing each component. The fluorescence imaging acquired by the station has been pre-processed by selecting regions of interest (ROIs) of 50 100 × pixels. A line regressing prediction method estimates the quality of kiwifruit samples. The results obtained in classification show that the station and prediction model enables the correct discrimination of kiwifruits internal sugar content and firmness with a percentage of r= 98.5%, SEP=0.4 and r=99.9%, SEP=0.62.
Numerical simulation of imaging laser radar system
Shaokun Han, Bo Lu, Ming Jiang, et al.
Rational and effective design of imaging laser radar systems is the key of imaging laser radar system research. Design must fully consider the interrelationship between various parameters. According to the parameters, choose suitable laser, detector and other components. To use of mathematical modeling and computer simulation is an effective imaging laser radar system design methods. This paper based on the distance equation, using the detection statistical methods, from the laser radar range coverage, detection probability, false-alarm rate, SNR to build the laser radar system mathematical models. In the process of setting up the mathematical models to fully consider the laser, atmosphere, detector and other factors on the performance that is to make the models be able to respond accurately the real situation. Based on this using C# and Matlab designed a simulation software.
Diagnosis of electron excited temperature in dielectric barrier discharge by photoelectric method
Yanzhao Zhang, Lifang Dong, Yajuan Hao, et al.
The electron excited temperature in dielectric barrier discharge under argon at atmospheric pressure is diagnosed by photoelectric method. The electron excited temperature Texc can be estimated by using spectral lines intensity ratio method. The spectral lines 763.72nm (2P6→1S5) and 772.63nm (2P2→1S3) in the spectrum range from 690nm to 800nm are chosen to estimate the electron excite temperature. The power of the discharge gap is calculated by analyzing the waveform of the apply voltage and the voltage of the test capacitance. The experimental results show that the electron excited temperature is in the range of 0.19-0.31eV and the discharge power in the gas gap is in the range of 35.7-51.0W under different discharge gap 0.9-3.0mm. In addition, it is found that the variation tendency of the electron excited temperature with the discharge gap increasing is similar to that of discharge power, and the electron excited temperature and discharge power has a minimum value at d=1.1mm. The discharge operates in glow-like mode when the discharge gap d<1.3mm, and the discharge operates in patterned mode when d>1.3mm. As the discharge gap increase from 1.3mm to 3.0mm, the streamer channels became brighter, and move faster. The self-organized behavior is also found in the experiment.
Study on nondestructive detection system based on x-ray for wire ropes conveyer belt
A nondestructive detection system based on X-ray for wire ropes conveyer belt is designed by X-ray detection technology. In this paper X-ray detection principle is analyzed, a design scheme of the system is presented; image processing of conveyer belt is researched and image processing algorithms are given; X-ray acquisition receiving board is designed with the use of FPGA and DSP; the software of the system is programmed by C#.NET on WINXP/WIN2000 platform. The experiment indicates the system can implement remote real-time detection of wire ropes conveyer belt images, find faults and give an alarm in time. The system is direct perceived, strong real-time and high accurate. It can be used for fault detection of wire ropes conveyer belts in mines, ports, terminals and other fields.
Laser photo-acoustic detection of nitrogen oxide
Guiyin Zhang, Yidong Jin
The absorption property of NO in the wavelength region of 420-470nm is surveyed by the technique of photo-acoustic (PA) spectroscopy. It is found that NO molecule is excited though multi-photon process. The optimum excitation wavelength in this region is decided when one detect NO with PA technique. It is 452.4nm or 429.6nm which corresponding to the transition of NO A2Σ(v'=0,1)←X2Π (v=0). The variation of PA signal versus buffer gas pressure and NO concentration is measured. It is shown that owing to the enhancement of V-T transfer energy with buffer gas pressure, the intensity of the PA signal increases when the pressure of the buffer gas is increased. But the PA signal is almost invariable when the buffer gas pressure is more than 5.32×104 Pa. The PA signal shows itself as linearity variation with NO concentration. Under the condition of standard atmosphere, a detection limit of 5ppm is obtained on the basis of SNR=1 with a homemade apparatus.
Simulation and software for lidar system
Shao-kun Han, Li-li Guo, Ming Jiang, et al.
Based on the theory of lidar system,a model of lidar system was established. We focus on the math model of the noise and the simulation of NEP and SNR, and designed relative programmes for it. In case of different existing models on transmitting system, air condition and detecting system, simulation for lidar system can be realized.
Study on the weak signal detection in the laser radar based on the chaos theory
Qing-wei Ping, Gui-fen Xia
In this paper, we present a new method for the weak signal detection in the laser radar, which is based on that the laser echo is characteristic with chaos. The method is naturally rooted in nonlinear dynamical systems and relies on neural networks for its implementation. At first, this paper used the observed data to analyze the chaotic characteristics of the laser radar backscatter by calculating the chaotic character parameters, including correlation dimension, Lyapunov exponent and local predictability. Then the predictor model based on BP neural network is proposed. Experiment results show that the BP neural network predictor is a better math model. It is valuable for signal detection in chaotic series.
Research on the data processing of photoelectric signal surveying for coal mine gas
Mengran Zhou, Zhenbi Li, Zongjiu Zhu
In view of the shortage of the former chemistry examination for coal mine gas it uses infrared spectrometry to monitor gas, and propose the principle of surveying the coal mine gas basing on infrared absorption spectrum methods, and has given the structure diagram of gas remote sensing alarm system. When infrared spectrum signal including the gas information goes through the photoelectric detection, then it goes through the Fourier spectroscope to obtain the signal, and does the enlargement transformation; at last the computer processes and recognizes the data. The theoretical analysis and the experimental result indicate that after the signal pretreatment including characteristic extraction, background deduction and normalized processing it obtains a standard standardized spectrum diagram. Based on gas member in 1.65μm absorption characteristic spectrum, when it is in before some background, the mine underground gas exists the infrared radiation information that could change and arrive to the sensor, and then the alarm system can survey these difference information and process it to confirm the gas density, when it is under certain threshold value the system will alarm. Through the comparison, it retrieves the gas density in mine. This method has overcome the traditional method such as gas chromatography hydrogen flame ionization detector with shortcoming of bad timeliness, has realized complete non-contact online automatic monitor, and really reflected the gas density.
Research on laser detection of underwater acoustic signals
A technique is developed to detect underwater acoustic signals by utilizing the resultant surface perturbations. It uses light wave in air and uses acoustic wave under water. Because two best channels are combined together, it is an ideal method for remotely detecting underwater acoustic signals. The underwater acoustic signal can cause the perturbations at water-air interface. These perturbations result in an amplitude modulation effect on a laser beam reflected by the water surface. The modulated underwater laser signal can be detected by using a direct light intensity detecting method. Based on the theory of modulation of the intensity of laser, a detection system was developed in the laboratory. By analyzing the massive experimental data, the technique of laser detection of underwater acoustic signals is validated.
Analytical study of terahertz wave intensity measurements by ZnTe electro-optic crystal
Muhammad Siddique, Suhui Yang, Zhuo Li, et al.
An analytical study of THz-waves' intensity measurement generated by Terahertz Parametric Oscillator (TPO) and detection of the THz pulses occurs via free-space electro optic detection by ZnTe crystal has been studied. The pump-probe technique has been used to observe the dynamics of an optically excited ZnTe electro-optic crystal. THz wave will be used as modulation source for electro-optical phenomena in ZnTe crystal. The THz pulses generated by TPO are 10-25 ns pulses at a repetition rate of 1Hz. ZnTe crystal is being used for intensity measurement of THz-waves. In this theoretical proposed experiment, a short pump pulse (THz-wave) and probe pulse (near IR laser) with duration of typically 10 to 25 ns interacts in the ZnTe. In electro-optic sampling the two effects namely Pockels effect and Kerr effect have been discussed and interaction of two beams from or transmission through the ZnTe, the probe pulse Intensity contains information about the THz-waves' intensity and so on.
Measurement of stable localized hexagonal states in dielectric barrier discharge by photoelectric method
Diverse stable localized states respectively with hexagonal, heptagonal and enneahedral symmetry have been observed in a dielectric barrier discharge system with two water electrodes. The interacting process of different localized clusters due to the attractive interaction is shown. The spatiotemporal dynamics of the localized hexagonal states are measured by photoelectric method. It is found that the seven filaments composing a hexagonal cell discharge nearly at the same time, with the light intensity of the central filament much stronger than its neighboring six ones. Magnifying the light signal, however, it is found that the discharge moment of the central filament always precedes that of others actually.
Detector array for measuring far-field energy density distribution of repetitively pulsed laser
Pengling Yang, Guobin Feng, Qunshu Wang, et al.
A system based on detector array is developed to measure the far-field temporal and spatial distribution and absolute pulse energy density of the laser beam. In this experiment, the duration of the laser pulse is about 15ns, the repetition rate is 400Hz, and the diameter of the far-field beam is about 60cm. The detector array is composed of 112 Si-PIN photodiode detectors and arranged to be a disk with spatial sample rate of 0.4cm-1. Charge sensitive amplifiers and baseline restoration circuits are used to collect photocurrent of the detectors, and current-input AD converters with integrator front-end are used to digitalize the multi channel signals. The far-field laser beam profile is reconstructed with the spatial sample data using special arithmetic of spatial interpolation. The system is capable for absolutely measuring far-field energy density distribution of repetitively pulsed laser, with response wavelength between 400nm and 1100nm, minimal detectable pulse duration of about 10ns, and energy density of 0.1-100μJ/cm2.
Application of an adaptive PI controller to the servo control system of a photoelectronic detection system
Ai Xiong, Yongkun Fan, Huimin Shen
Controller performance plays an important role in the servo control system of the photoelectronic detection system. However, it is difficult to redesign the controller parameters in real time when the system performance degrades. This paper proposed an adaptive PI controller using Model Reference Adaptive Control (MRAC) techniques with the MIT rule and applied it to the current-loop of the servo control system. In the MRAC, the desired behavior of the process is specified by a model, and the parameters of the controller are adjusted based on the difference between outputs of the closed-loop process and the model. The MIT rule is an adjustment mechanism that makes the error becomes zero. The presented algorithm is carried out in two steps. Firstly, given the time and domain specification, a reference model based on the open-loop transfer function of the plant and a PI controller is designed to parallel with the real process. The adaptation gains of the MIT rule and the external signal are determined to guarantee the convergence of the parameters of the PI controller and minimize the squared model error. Secondly, the adaptation is started and the process is excited adequately in order to enable the parameter adaptation to take place. When the parameters have adapted after a period of time, then the adaptation was stopped and the PI controller operates again with fixed parameters. The proposed algorithm was simulated on the servo control system of the photoelectronic detection system and the results show the effectiveness of the algorithm.
Behavior analysis of an organic polymer optical multi-stable lasing system
Junqin Feng, Fugen Wu, Tingwan Wu
This paper presents some new study results on stability analysis of an organic polymer optical multi-stable lasing device based on the Poincare nonlinear theory. The dynamics of light field in the medium are described with the extended forced oscillation model of optical multi-stable and lasing system. These nonlinear equations are firstly expanded as a Taylor series and the nonlinear terms are ignored, then linear equations are obtains. Under the small perturbation these linear equations have the same properties as the nonlinear equations. Therefore, the linear system can be instead of the nonlinear system for stability analysis. Moreover, through the theoretical analysis and numerical analogue, the region of stability or instability (attractors or repellors) is discussed by eigenvalue of the linear equations coefficients matrix. Meanwhile the type of stability or instability is given. Finally, theoretical and numerical analyzing shows that the regions of stability are some different from the previous research results. These results should be significant in some degree for an organic polymer optical multi-stable lasing device research. In the low branch of instability, the incident light field of the transient response keeps attenuation oscillation, and the spectrum of frequency is not dispersible spectrum. Numerical simulation shows that the system appears special output characteristics and dynamic behaviors with the step signal and analysis this dynamic behavior on phase position map. Judge these behaviors with Lyapunov exponent.
Study on the wavelength characteristics of the emission patterns in dielectric barrier discharge by photoelectricity method
A dielectric barrier discharge system is specially designed with two liquid electrodes and a corresponding photoelectricity detection system. The detection system is composed of lens, apertures, multiplier-tube, digital camera, and an oscilloscope. A rich variety of emission patterns are obtained in the system as the voltage is increased. The wavelength characteristic of the emission patterns in dielectric barrier discharge is investigated. It is found that the wavelength of the emission patterns displays a non-monotonic variation as the applied voltage is increased. When the applied voltage is relatively low, the wavelength of the emission patterns decreases as the applied voltage increases. When the applied voltage is increased over a critical value, the wavelength of the patterns becomes larger as the voltage is increased. The wavelength of the emission pattern may maintain approximately invariable when the voltage is increased within some particular voltage range.
Research on ship wake detection by optical method of small angle forward scattering
Donghua Zhu, Jionghui Rao, Xiaohui Zhang, et al.
A ship wake in the ocean contains lots of microsize air bubbles with diameter of 10μm~200μm. When a beam of light propagates through the ship wake, it leads to attenuation of the light energy and change of its spatial distribution due to absorption and scattering caused by ocean water and bubble mass together, but they don't share the same scattering mechanism, leaving absorption out of account. Scattering from micro bubbles can usually be explained by Mie scattering theory. In this paper, a method based on optical scattering theory is proposed for detecting the target of ship wake in the ocean, and an experimental system is built up according to the Lambert-Beer law. In the experiment, a semiconductor laser with wavelength about 532nm was employed as the light source, an experimental device which modeled the target of a ship wake to generate bubble mass in water, and a high-speed PIN photodiode as the detector. Besides, the optical receiving system included a set of optical lens and apertures, which were employed to limit the field of view(FOV) of the receiver detector. After measurement of the small angle forward scattering rays scattered from bubble mass with a small FOV, the target signals was got and processed. Then adjustments were made to the optical receiving system and experiments were implemented with varying the FOV to find out the influence of FOV on target signal SNR and obtain the optimum FOV. The results showed that adjusting the FOV according to different microbubble size density could improve SNR.
High speed online thin steel laser drilling and marking system
XueSheng Liu, YingHua Cao, Xin Yan, et al.
High beam quality pulsed Q-switched Nd:YAG solid-state laser 450m/s high speed online laser drilling and marking system is reported. By PCL-836(A) realizing the control of laser power supply, AQ-switcher and two-dimension scanner. Synchronizing pulsed laser and AQ-switcher through the delay of industry computer, and realizing short pulsed width for laser drilling, long pulsed width for laser marking through setting the releasing time of laser power supply. And adopting the two-dimension scanner to catch up with the high speed moving thin steel, which keeps the laser and steel relatively inaction. Drill at different positions of the moving steel, and use the pinhole to test the drilled holes.
Distributed fiber optic perturbation locating sensor based on dual Mach-Zehnder interferometer
Guangming Luo, Chunxi Zhang, Lijing Li, et al.
This paper studies a distributed fiber optic perturbation locating sensor used for security system, which is based on dual Mach-Zehnder interferometers. This system consists of two Mach-Zehnder interferometers with the common sensing arm, reference arm, two couplers and one laser source. This kind of distributed fiber optic perturbation locating sensor is very suitable for the measurement of the phase shift induced by some perturbation such as strain and vibration. When perturbation exerts on the sensing arm, a time delay will generate between the two output signals of the dual Mach-Zehnder interferometers. From the time delay, the location of the perturbation can be obtained. Experimenting on the type disturbance's optic cable and forcing on the 18.46km long distance fiber, the system correctly shows the position for real time and the average error is 390m. The experiment shows that the system can be applicable for locating on 40km distance fiber cable when the power of the laser resource increases to 300μW.
High-speed well-logging cable telemetry system based on correlative encoding
The common seven-core well logging cable can be able to transmit the maximum rate of 200kb/s for base band signal. This situation causes great difficulty in increasing signal transmission rate. In this paper, a high-speed well-logging cable telemetry system scheme was proposed. Based on correlative encoding and considered perpendicular multi-levels amplitude modulation to increase carrying signal for each code at the same time, and adopted equilibrium technique in time domain to spread the transmission bandwidth of well logging cable, a high-speed well-logging cable telemetry system scheme was designed. The simulated results indicate that after technique improving, the transmitting rate of seven-core well logging cable may be increased up to 400-500kb/s. This system has the advantages of taking less space, low power consumption, transmitting faster and easy for repairing or upgrading. Also the system can meet the basic need of the data transmitting speed demand of imaging well-logging system at the time begin.
An eye-safe coherent lidar for speed measurement
Zongfeng Ma, Chunxi Zhang, Pan Ou, et al.
An eye-safe, coherent Doppler Light Detection and Ranging (CDL) system for speed measurement under development at BUAA's School of Instrument Science and Opto-electronics Engineering is introduced in this paper. It consists of a 1.55-μm Er-doped fiber laser transmitter, a monostatic optical antenna, a single-mode fiber (SMF) interferometer, an InGaAs photodiode detector, and signal processing equipments. All devices of optical circuit are connected by SMFs making the system reliable and setup arrangement flexible. The goal is to give the evaluations of the Doppler frequency shift and platform speed. Since the speed accuracy is time-independent, the CDL system can be used for integrated navigation system. The quality of Doppler-shift estimation by a spectrum analysis technique, fast Fourier transform (FFT) algorithms, ameliorates as the signal-to-noise ratio (SNR) increases. For the developed CDL system incorporating with SMF interferometer, only the light beam of mode LP01 is permitted to propagate, therefore the SNR is improved greatly. Experiments were performed on a moving hard target with the CDL system and the results were presented.
45 degree coupling loss for non-round fiber core in the Lyot fiber depolarizer
Lei Fu, Zhengfeng Zou, Shufen Chen, et al.
There is a coupling loss at the joint of the Lyot depolarizer consisting of two sections of birefringent fiber (Polarization Maintaining fiber or PM fiber) with non-round fiber core. The contribution to the loss for the non-roundness of the fiber core was calculated and analyzed using a method based on second moment. And the result obtained is in agreement with the experiment and so demonstrates the exist of the loss. This also provides a method of analyzing and calculating the coupling loss for non-round fiber core in the paper and is useful for manufacturing the Lyot fiber depolarizer and researching on the stability of the depolarizer type of a single mode interference fiber optic gyro (IFOG).
Depths of view and focus of digital holographic imaging system
Huaying Wang, Baoqun Zhao, Yi Wang, et al.
There exist some ambiguities about the depth of view (DOV) and depth of focus (DOF) of digital holographic imaging system (DHIS). Based on the principle of digital holography, the DOV and the DOF of the DHIS is analyzed in detail for the first time to the best of our knowledge. For the four common configurations for recording digital holograms, the axial complex amplitude and the intensity distributions of the reconstructed optical field of a point object are deduced respectively using Fresnel diffraction formula. According to the same criterion in common coherent imaging system of the lens (CCISL), the DOF of the DHIS is obtained. The results show that the DOV and the DOF of the DHIS are related not only to the optical wavelength and the numerical aperture of the CCD camera but also to the offset of the reference light wave. The DOF of the CCISL is found larger than that of the digital in-line holographic system. But the DOF of the digital off-axis lensless Fourier transform holographic imaging system, which is depended strongly on the offset of the reference point source, may be larger or smaller than that of the CCISL. The computer simulation results confirm the validity of the theoretical analysis.
Optimal scanning function for capturing segmented mirror in space optics system
A great deal segmented mirror errors consisting of piston and tip-tilt exist when space large aperture segmented optics system deploys. These errors will result in the departure of segmented mirrors images from the view. For that, proper scanning function should be adopted to control actuators rotating the segmented mirror, so that the images of segmented mirror can be put into the view and placed in the ideal position. The key of capturing segmented mirror images is selecting an optimal scanning function. This paper put forward the optimal scanning function principle based on capturing images by the fastest velocity. The scanning functions, such as screw-type, rose-type, and helianthus-type and so on, have their own merits and demerits. In my paper, the scanning functions above will be analyzed and discussed. As a sample, a simulation experiment is carried to study the effects of different scanning functions on three mirror astigmatism system, whose primary mirror with six segmented mirror. In simulation experiment, the piston and tip-tilt errors scale and the ideal position of segmented mirror are given, three scanning functions above are used to realize the capture process by utilizing the improved optics design software ZEMAX, the relationship between scanning functions and optical system are analyzed and the optimal one is determined.
Multistage wavefront control for a segmented primary mirror with annular-sector subaperture
Segmented primary mirror has been widely used in high-resolution ground-based and space-based telescopes. In this paper, we mainly discuss the wavefront control issue for a segmented primary mirror with annular-sector subaperture. In order to balance the requirements of correction in amplitude and spatial frequency, we propose a multistage wavefront control strategy and allocate the wavefront errors in spatial frequency domain. The power spectral density (PSD) is calculated to obtain the spatial frequency information of wavefront aberrations. The feasibility of the control strategy is verified by numerical simulation.
Improved cutback method measuring beat-length for high-birefringence optical fiber by fitting data of photoelectric signal
Zhi-Dong Shi, Jian-Qiang Lin, Huan-Huan Bao, et al.
A photoelectric measurement system for measuring the beat length of birefringence fiber is set up including a set of rotating-wave-plate polarimeter using single photodiode. And two improved cutback methods suitable for measuring beat-length within millimeter range of high birefringence fiber are proposed through data processing technique. The cut length needs not to be restricted shorter than one centimeter so that the auto-cleaving machine is freely used, and no need to carefully operate the manually cleaving blade with low efficiency and poor success. The first method adopts the parameter-fitting to a saw-tooth function of tried beat length by the criterion of minimum square deviations, without special limitation on the cut length. The second method adopts linear-fitting in the divided length ranges, only restrict condition is the increment between different cut lengths less than one beat-length. For a section of holey high-birefringence fiber, we do experiments respectively by the two methods. The detecting error of beat-length is discussed and the advantage is compared.
Ultrasonic transmitter for coded excitation in medical endoscope imaging system
Shijie Wen, Xiaodong Chen, Jing Bao, et al.
In this paper, we introduced an ultrasonic transmitter for coded excitation used in medical ultrasonic endoscope, which is mainly composed of MD1211 and TC6320. Since the ultrasonic endoscope uses a miniature ultrasonic probe whose length is no more than 14mm, and the diameter is no more than 2.2mm, the ultrasonic excitation power is very low, which makes it difficult to obtain a sharp image. So it is very important to use coded excitation to enhance image quality, which can improve the SNR of the echo without degrading the axial resolution. The transmitter accepts coded signals from FPGA and transforms them to ±60V driving signals which are sent to transducer, making it easy to implement coded excitation in ultrasonic endoscope.
Subwavelength imaging with two dielectric planar waveguides
Min Cheng, Yuliang Li, Xiyao Chen, et al.
In this paper, we investigate the possibility of superlensing with two dielectric planar waveguides in detail by studying the transmission of evanescent waves through one double-waveguide structure. We derive the total transmission and reflection coefficients for the double-waveguide structure. It is found that when one field component of an evanescent wave coincides with one of the single-waveguide bound-state eigenvalues, the total transmission increases exponentially with respect to the distance between two dielectric planar waveguides, and zero reflection can be found. An important interplay between propagating waves and evanescent waves on image formation is revealed, which makes the appearance of the image of a superlens substantially different from that of a real image behind a free space. We derive the resolution of the double-waveguide structure and infer that resolution arbitrarily smaller than the wavelength should be possible in principle, provided that sufficiently high dielectric contrast of two waveguides can be obtained. The numerical results confirm the qualitative discussions in this paper.
Detection of TNT in acetone using Raman spectroscopic signature
Xiaofeng Wang, Shengli Chang, Jiankun Yang, et al.
The detection of explosive agents is becoming more important and receiving much greater emphasis for homeland defense. Raman spectroscopy is a well established tool for vibration spectroscopic analysis and can be applied to the field of explosives identification and detection. The major bands of the Raman spectroscopy of industrial TNT (Trinitrotoluene, CH3C6H2(NO2)3) are analyzed and seven prominent peaks, that is 1616.9cm-1 (C=C aromatic stretching vibration), 1533.9cm-1 (NO2 asymmetric stretching vibration), 1360.1cm-1 (NO2 symmetric stretching vibration ), 1210.5cm-1 (C6H2-C vibration), 822.9cm-1 (nitro-group scissoring mode), 792.3cm-1 (C-H out-of-plane bend), and 326.7cm-1 (framework distortion mode) are used to identify the TNT. The Raman spectroscopes of TNT solved in acetone at different mass ratios are studied, and the TNT in the solution can be detected correctly according the relative distance, intensity, and peak area of the seven peaks. The TNT prominent peaks appear clearly in high level solution (the mass ration of TNT and acetone is more than 1:10). With the decrease of TNT concentration in solution, the signature of TNT becomes more and more weak. The low detection limit of TNT is limited by the noise of the instrument (NXR FT-Raman accessory module with Nicolet 5700 FT-IR spectrometer is used for our experiments. The low detection limit in our experiments is mass ratio 1:200, which is about 4mg/mL). The prominent peak heights are discussed in consideration of the TNT concentration. Taking one of the acetone's peaks (1716.9cm-1) as the internal standard line, the relative height of the prominent TNT peaks is almost proportional to the concentration of the TNT in the solution. A fitting curve for the relations of prominent peak height according to the concentration is proposed with multinomial fitting method, which can be used to analyze the concentration of TNT more accurately.
Characteristics of intensity modulation in single-mode microchip Nd:YAG lasers with anisotropic feedback and its applications
Yidong Tan, Shulian Zhang
The characteristic of laser intensity modulation in microchip Nd:YAG lasers with anisotropic feedback is presented, on which a force measurement scheme based is demonstrated. The measurement system is composed of a microchip Nd:YAG laser, a birefringence element (BFE), and an external feedback mirror. Due to the birefringence effect of BFE, the external cavity modulates the laser intensities in two orthogonal directions with a phase difference (PF), which is twice as large as that of the BFE. If a photoelastic element with force loaded on is served as BFE, the PF between two in-quadrature laser intensities is proportional to the force loaded on the photoelastic element. Thus, the force can be easily and conveniently obtained from the PF between two in-quadrature laser intensities. A theoretical model is put forward and is in good agreement with the experimental results. Moreover, the results here can also be applied to displacement measurement. Our researches broaden the optical feedback in application for precision measurement.
Power measure and control system for high power laser in real-time
Bo Li, Youqing Wang, Dengfeng Peng, et al.
A new kind of measure and control system for high power CO2 lasers in real-time is designed in order to improve stabilization and accuracy of lasers power, and includes tow parts, one is the sample unit, made of a rear mirror, an integrating sphere and an infrared detector, the other one is the and feedback control unit made of a PID controller. This system adjusts output power of the lasers and makes the laser power stable in the required scope by the closed-loop control system according to the feedback of laser power signal, which depends on the sampling of laser power transmitted out of the rear mirror of the resonator. This system can detect and monitor the laser power on line and has no influence on the output laser beam. It greatly enhances the stabilization (<±0.3%) and accuracy of the control. Furthermore, it has such advantages as: compact construction, high stable performance and fast response and no need to intercept the output laser beam just as the monitor with rotating pin sampling.
All-optical wavelength converter with recirculating configuration based on self-phase modulation in a highly nonlinear photonic crystal fiber
A novel scheme is proposed to achieve all-optical SPM-based wavelength conversion in a bismuth oxide-based highly nonlinear photonic crystal fiber. It consists of erbium-doped fiber amplifier, optical circulator, Fiber Fabry-Perot filters, photonic crystal fiber and fiber Bragg grating. Owing to SPM, a recirculating configuration is designed to induce the further spectral broadening and wavelength conversion is achieved with a tunable Fiber Fabry-Perot filter. The simulation results of bismuth oxide-based photonic crystal fiber indicate that the effective index of the fundamental mode increases monotonically with the increase in the hole pitch, or the decrease in the ratio of the hole diameter to the hole pitch. The mode effective area steadily increases with the hole pitch. The nonlinear coefficient, which is beneficial to shorten the fiber length and reduce the required optical power, is expected to be 1100W-1km-1 by using bismuth oxide-based glass with high nonlinear refractive index and reducing the effective core area with holey microstructure. The mode-field diameter of bismuth oxide-based is estimated to be 1.98μm and the predicted small effective core area is 3.3μm2. The propagation loss at 1550nm is about 0.8dB/m. The obtained results show that SPM-based PCF-WC has a potential of wide conversion bandwidth, high response time, simple configuration and low insertion loss etc.
Research on photoelectric detection technique applied to underwater detection system using pulsed laser
Jionghui Rao, Gang Lu, Kecheng Yan, et al.
Unlike optical detection of air targets, detecting underwater targets by optical technique is more complicated because of strong backscattering and absorption attenuation caused by water itself while rays propagating underwater. If a pulsed laser is employed as the active illuminator of an underwater detection system, it's possible to decrease the effect of backscattering light from water to a large degree and improve detection distance of the system consequently. In this paper, a set of underwater optical detection system is designed. This system can be used to detect underwater targets or micro bubbles in water. In order to optimize the system's performance, different photoelectric detectors are used in the system and contrastive experiments are implemented. A high-speed PMT and a high-speed PIN photodiode are employed without adjusting other system components. Accordingly, optical receiving systems and amplification circuits were designed, and a series of contrastive experiments were implemented. In these experiments, a board and micro bubbles mass works as targets which are placed in changing distance to detection system. By analyzing of the experimental results, it is concluded that both of the PMT and PIN detector can detect the reflected signal of board and micro bubbles effectively in a certain range. And they can be used in different applications because of their different characteristics.
Observation and analysis of water inherent optical properties
Deyong Sun, Yunmei Li, Chengfeng Le, et al.
Inherent optical property is an important part of water optical properties, and is the foundation of water color analytical model establishment. Through quantity filter technology (QFT) and backscattering meter BB9 (WETlabs Inc), absorption coefficients of CDOM, total suspended minerals and backscattering coefficients of total suspended minerals had been observed in Meiliang Bay of Taihu lake at summer and winter respectively. After analyzing the spectral characteristics of absorption and backscattering coefficients, the differences between two seasons had been illustrated adequately, and the reasons for the phenomena, which are related to the changes of water quality coefficient, had also been explained. So water environment states can be reflected by inherent optical properties. In addition, the relationship models between backscattering coefficients and suspended particle concentrations had been established, which can support coefficients for analytical models.
Studies on the transmission performance of SCI avionic optical data bus
Jian Cui, Zheng Zheng, Zheng Li
The transmission performance of SCI avionic fiber-optic data bus is analyzed in this paper. An analysis on the relationship between the transmission range and the data rate under certain attenuation and dispersion is presented. A simulation of the receiver with the M-sequence data and trapezoid pulses as input data stream is discussed in detail, the relationship between the sensitivity of the receiver and its bandwidth is simulated. The transmission delay due to the bandwidth of receiver is calculated too. Some operational suggestions on how to apply SCI fiber-optic data bus to the avionic field are given.
TriOS underwater spectrum measurement system and its application
Chengfeng Le, Yunmei Li, Deyong Sun, et al.
Light is very important for water ecosystem, it was attenuated because of absorption and scatter caused by suspend sediment, chlorophyll and colored dissoluble organic matter(CDOM) in water. Water remote sensing reflectance is an important parameter for ocean color remote sensing, which has good relation with water quality. Measure underwater spectrum has significance application value for water ecosystem research and water quality retrieval. This paper introduced the TriOS spectrum measurement system firstly, then use the in situ data collected by the system in Taihu Lake to retrieval suspended sediment(SS) concentration. First, underwater remote sensing reflectance(Rrs(0-)) was calculated by using the underwater spectra, then transform the Rrs(0-) into Rrs(0+) based on water-air interface transmission model, after that analysis the relativity between SS concentration and Rrs(0+), and finally suspend sediment retrieval models were developed. Compare different models, in order to select an optimal model for retrieving SS concentration. The result indicates that: Rrs(0+) has good relationship with the logarithm of SS concentration(Ln(SS)). In spectral region 500nm-600nm, there present negative correlation, and present well positive correlation in spectral region 620nm-882nm. The maximal correlation coefficient locates at band 743nm. Take Rrs(522), Rrs(743), Rrs(815) as independent variable to build SS concentration retrieval models, the retrieval results showed that logarithm model is better than other models, it can satisfied the require of practical application to certain extent.
The infrared imaging characteristics of heating-radiator faults
Si-chao Liu, Hua Dong, Shuang-xi Zhang, et al.
There are various faults in the running of heating-radiator which have severely impacted on heating-radiator system operation. It is desired to develop an objective methodology to predict the heating-radiator faults instead of experiential judgment. On the infrared temperature-measuring principle, the temperature field will distort when some faults happen in the running of heating-radiator. To identify heating-radiator faults better, the fault modes of heating-radiator are approximately divided into three types-quality fault, corrosion fault, and running fault. With the infrared imaging characteristics of the surface temperature of heating-radiator, the faults of the copper-aluminum radiator and irregular-tube radiator can be detected combining heating-radiator's structure, technics and running conditions. The results proved that the infrared thermal imager is a novel, effective and visual approach to detect heat-radiator faults and have a wide application prospect.
Analysis and experimental study of the temperature and stress distribution in the slab of a solid-state heat capacity laser
Jiankun Yang, Xuebin Wan, Xiaojun Xu, et al.
In conventional cooling operation, thermal effects and stress distribution in slabs of solid-state laser are presented by many workers, it is different with that in the solid state heat capacity laser. In this paper, the transient temperature and stress distribution in Xeon flash lamps pumped slabs for single-shot and repetitively pulsed operations will be produced in the heat capacity operation. A high speed CCD camera was used to set up an experiment system to measure the interference fringes, from these fringes' changes, the extension of the slab due to the stress and thermal expansion can be obtained. Since dielectric materials are inherently several factors stronger in compression than in tension, this temperature reversal in heat capacity operation increases the inherent fracture limit of the system and allows a heat capacity operated laser to be pumped much harder than a conventionally operated slab laser.
Scanning rain gauge based on photo electricity
Fei-long Huang, Yuan-hong Li
A non-contact rain gauge with photo electricity technology is introduced in this paper. Dimensional distribution of rain inside a traditional rain gauge does not need to be changed, and the rainwater falls freely to the ground, so this new rain gauge doesn't need to be cleared as a traditional rain gauge does frequently. And then a capacitor is used as a switch that would drive LED light to scan and drive photo electricity inducing element Charge Coupled Device (CCD) to detect when it is induced by the falling drips. Light through a convex lens would scan the drips and project them on CCD across. Electrical signal is produced when CCD detects the shadow after another convex lens. The drips whose diameter is 0.3 millimeter can be distinguished and so as smaller drips of 0.1 millimeter if high-resolution CCD is used. After an amplifier the electrical signal would be transformed into digital signal and would be used to calculate the volume of rain. The Central Processing Unit on main control board gives commands to scanning trigger and controls interrupts from process of data acquisition and calculation. The non-contact photo electricity measurement can detect raindrops of different size. Parallel light projects every raindrop in space on CCD and tells its diameter exactly. So it gives satisfying precision and other useful data such as spectrum of raindrops. Further more, velocity of raindrop would be acquired according to its size. The system needs low cost with universal CCD and Single Chip Micyoco (SCM), and it is worth advocating.
Optical analysis and design for the laser remote sensing underwater acoustical signal
Laser remote sensing underwater acoustical signal is one effective way to recognize underwater targets and realize on-board active scanning, acquisition, pointing and tracking over a wide range. By the research of the theoretical and the simulation of PC, one fundamental experiment system is constructed, which validates the feasibility of laser detection of underwater acoustic signal. The size and location of the diaphragm of the detection system are particularly discussed and one optimum diaphragm aperture was developed. The affection of the incidence beam width is also analyzed. By selecting the very incident angle and beam width, we can get the best performance. These conclusions has the important guiding significance to the technology of laser remote sensing underwater acoustic signal. As a whole laser remote sensing underwater acoustic signal has its own advantages and opens up broad possibilities for the practical application. Of course it still has something to do to improve its performance, which worth doing further studies.
Design of device for observing the solar on the moon in multispectrum of extreme ultraviolet
Gang Huang, Qirong Xiao, Chao Zheng, et al.
Solar EUV band has a very important meaning of detecting the physical processes and its controlling factors of solar surface, and the Earth's environment as well as changes in the Earth's climate. In the thesis we introduce the basic design of the solar ultraviolet telescope and imaging system .Because of small-band transmission of the vacuum ultraviolet optical prism, we take double-Cassegrain reflector optical system. The sunlight could be gathered to CCD detection system in order to image the sun in three specific spectrums involving 30.4nm, 58.4nm and 121.6nm. The reason we choose the center wavelength of 30.4 nm. 58.4nm and 121.6nm is that these three spectrums contain a lot of bright lines, have a great radiation flux and play a significant role in ionizing and heating the Earth's upper atmosphere. We make UV telescope imaging system and ultraviolet light as a whole, then pump the whole system into vacuum to simulate space environment. We introduce the calibration device in our system innovatively. Our thesis gives a detailed description of the way of simulation of optical design, the vacuum system design and system calibration. Owing that our system have the characteristic of Lightness, simple structure, small power, it is rather fit for astronomical observations on the moon. The imaging results could provide very important research data for the middle and upper atmospheric composition and ionospheric electron changes in density and communications research.
Design of a night vision system with laser illumination based on DSP
Yang Liu, Wen Xiao, Haiyang Wang
According to characteristics of infrared imaging in darkness, a night vision system with laser illumination based on embedded structure was developed. The system detected remote target at night with a high-power infrared semiconductor laser diode as illuminating source, overcoming the defect of weak energy in passive imaging system. A reliable driver was designed to stabilize output power of the laser. Technologies were adopted to improve performance of the source greatly, such as slow start-up circuit, current interruption protection and over-current limit circuit. The illuminating source met the needs of detection in various distances and achieved satisfying transmission effect. The imaging part, where TMS320C6713 served as the center processor, realized functions of image capture, processing and export. As is known, infrared image has defects of small dynamic range and low contrast. Otherwise, the source, environment and electronic devices brought various noises that reduced image quality. Algorithms of image enhancing and noise inversion were designed correspondingly, which filtered noises and restrained background influences to gain high contrast of the target. Compared with traditional image processing based on computer, the adoption of DSP not only greatly improved image quality, but also made this system miniature and portable. The system could capture real-time image of remote target in 3~5km accurately in starless nights or under poor weather conditions.
Reconstruction algorithm improving the spatial resolution of Micro-CT
Jian Fu, Dongbo Wei, Bing Li, et al.
X-ray Micro computed tomography (Micro-CT) enables nondestructive visualization of the internal structure of objects with high-resolution images and plays an important role for industrial nondestructive testing, material evaluation and medical researches. Because the micro focus is much smaller than the ordinary focus, the geometry un-sharpness of Micro-CT projection is several decuples less than that of ordinary CT systems. So the scan conditions with high geometry magnification can be adopted to acquire the projection data with high sampling frequency. Based on this feature, a new filter back projection reconstruction algorithm is researched to improve the spatial resolution of Micro-CT. This algorithm permits the reconstruction center at any point on the line connecting the focus and the rotation center. It can reconstruct CT images with different geometry magnification by adjusting the position of the reconstruction center. So it can make the best of the above feature to improve the spatial resolution of Micro-CT. The computer simulation and the CT experiment of a special spatial resolution phantom are executed to check the validity of this method. The results demonstrate the effect of the new algorithm. Analysis shows that the spatial resolution can be improved 50%.
Modulation-free frequency stabilization of laser-diode-pumped single frequency solid state laser
Xiu-yong Zhang, Chun-qing Gao, Ming-wei Gao
In this paper the modulation-free frequency stabilization of laser-diode pumped single frequency solid-state laser was reported. The principle of generating a dispersion-like frequency-discrimination curve using a confocal Fabry-Perot cavity (CFPC) was introduced. In the experiment a LD-pumped 1319 nm monolithic non-planar ring oscillator (NPRO) single frequency Nd: YAG laser was used. With the modulation-free frequency stabilization method, the laser was locked to the resonance frequency of the CFPC, whose jitter frequency was less than ±500 kHz in the time of 30 minutes estimated from the locked error signal.
SLR system improvement for GIOVE-A satellite observation
You Zhao, Cunbo Fan, Xingwei Han, et al.
Galileo system consists of 27 satellites distributed in three uniformly separated planes. At the end of 2005, one satellite, Galileo In-Orbit Validation Element-A (GIOVE-A), was launched as planned into an MEO with an altitude of 23,260 kilometers. Carrying a payload of rubidium clocks, signal-generation units, and a phase-array antenna of individual L-band elements. GIOVE-A started broadcasting on January 28, 2006, securing the frequencies allocated by the ITU for Galileo. Performance of the on-board atomic clocks, antenna infrastructure, and signal properties is evaluated through precise orbit determination, supported by Satellite Laser Ranging (SLR), an independent high-precision range measurement technique for orbit determination based on a global network of stations that measure the round-trip flight-time of ultra short laser pulses to satellites equipped with laser retro reflector arrays (LRAs). SLR provides instantaneous range measurements of millimeter-level precision which can be compiled to provide accurate orbits and to measure the on-board clock error. Given the importance of SLR data for the characterization of the GIOVE-A clocks, the Changchun SLR station in northeast China was selected among the Chinese stations contributing to the ILRS because it had demonstrated strong MEO satellite tracking; collocation with an existing International GPS Service station; and good weather conditions. This paper introduces the SLR system improvement for tracking GIOVE-A satellite in Changchun station. During the more than two months improvement, the new servo and encoder systems were installed, primary mirror, second mirror and some other mirrors have been cleaned and recoated, and the laser system was adjusted in order to improve the laser efficiency and output energy. The paper gives out the improvement results, and the GIOVE-A satellite observation results.
Technical methods for SLR daylight tracking
You Zhao, Xingwei Han, Cunbo Fan, et al.
The daylight tracking observation is necessary and the tendency of Satellite Laser Ranging (SLR) in the future. More than half of the SLR stations in the world can take the daylight tracking observations. From the experience of the most successful stations around the world, Changchun station has been working on the daylight tracking technique in recent years. This paper introduces the performance and progress for SLR system daylight tracking in Changchun station. It first introduces the problems and difficulties facing this system for daylight tracking - mount model, the separation of emitting and receiving parts of the telescope, control range gate, and installing narrower filter. Secondly, it presents some work which has been done in the system for daylight tracking: system stability improvement, laser stability improvement, mount model adoption, control system, etc. From these analysis and work which has been done, the system performance has been greatly improved. A routine operation system for daylight tracking observation has been set up.
Design of IDT for MOEMS angular velocity sensor
Yi Zhao, Shufen Chen
The paper presents a novel structure design of Micro-Optic-Electro-Mechanical-System (MOEMS) angular velocity sensor and calculates the design parameters of InterDigital Transducer (IDT). The structure includes light readout system, SAW sensor system and signal processing system. A special point in the structure is adding a optical readout device based on the traditional SAW typed MEMS angular velocity sensor, there would be apparent advantages of higher precision, stronger anti-vibration capacity, and lower difficulty of processing techniques. SAW sensor is the key part of this design, its quality affects the sensitivity of Angular velocity sensor. In this paper, we calculated and simulate the parameter of IDT for MOEMS Angular velocity sensor.
Digitization and compensation of the open-loop fiber optic gyroscope
Ming Jiang, Lingcao Wang, Shaokun Han
The fiber optic gyroscope plays an important role in the family of inertia devices. But in the dynamic condition, Because of the nonlinear output and the nonlinear graduation factor and zero-bias by temperature, the open-loop FOG can't apply in some fields. Therefore, how to reduce the bad affection by temperature is urgent. This article proposed a new method to digitize the open-loop FOG and compensate the temperature error and nonlinear graduation factor. This detection circuit for FOG is mainly based upon C8051F350 MCU. There are 24 bit A/D converter and temperature sensor. What is more important, its area is only 5×5 mm2, which is propitious for minimizing and engineering. By analyzing and researching a great of experience data, we build the model of zero-bias temperature character, graduation factor temperature nonlinear character and output nonlinear character. Then we compensate the character mentioned above. Test result shows that the system reaches the expected performance. It is meaningful for engineering, minimizing and application.
Realization of performance test system for fiber optic gyroscope based on LabVIEW
Ming Jiang, Zhaofang Wen, Liping Wang
This paper presents the realization of a performance test system for fiber optic gyroscope, the test data are gathered to PC through serial port. A Software Program is also developed based on LabVIEW, it can calculates a lot of performance parameters of fiber optic gyroscope, saves the result in text files and display it in real time. It makes the test course very convenient and easy.
Optical fiber acoustic and ultrasonic sensor based on Fabry-Perot interferometry
Zhenwu Guo, Weixiang Li, Dapeng Zhang, et al.
We designed a optical fiber acoustic and ultrasonic sensor probe based on Fabry-Perot interferometry, and gave the principle structure of the sensor: The two mirrors of Fabry-Perot interferometer are composed of the fiber's end face and the aluminum thin diaphragm, outside sound wave will force the thin diaphragm vibration, it is also to say the Fabry-Perot cavity length varies with the sound wave, thus the output intensity of the interferemeter is modulated by the wave, at last the photodetector(PD) transforms the light intensity signal to electric current signal. The thickness of the aluminum thin diaphragm is 10μm only, and its radius is 1mm, as a result the sensitivity of the sensor is very high. But if placing the sensor in liquid at a deep point, the static pressure would make the thin diaphragm crushed because the static pressure of the liquid is very strong compared with sound wave. For this reason, we design a kind of small scaled air bag linked with the Fabry-Perot cavity which spread the sensor an ability of being able to stand of the static pressure. The maximum of static pressure the sensor could stand has improved from 0.3 MPa to 10 MPa above, so the sensor may work normally at point of 1000m under water surface. The result of experiment in water show that the sensor sensitivity reaches -162dB(0dB=1rad/μPa), the frequency response range is from 1KHz to 5 MHz. The sensor is fit for detecting acoustic and ultrasonic signals in liquid.
Research on measurement method of LED optical parameters
Fang Liu, Yue-jin Zhao, Li-chang Wang
Photometric and colorimetric parameters are important evaluations criterion of the performance of LED light sources. Photometric and colorimetric parameters of LED were measured using PMT spectroradiometer and CCD spectrometer respectively in this research, the result was discussed and the common method was improved. The result of experiment indicated that temperature drift of PMT spectroradiometer was compensated effectively by introducing reference standard light source; measurement accuracy of CCD spectrometer was improved significantly with standard LED. CCD spectrometer suitable for the industrial application for its rapid measuring speed, PMT spectroradiometer should be used in scientific research for its high measurement accuracy according to the experimental results.
Study on auto urine analysis system based on CCD technology
Guoying Li, Lianqing Zhu, Mingli Dong, et al.
This paper introduces the principle and configuration of an auto urine analysis system. The system employs an ARM-LPC2214 as CPU and a color linear-CCD as sensor. A CPLD is used to produce pulses for the CCD and for other circuits in the system. The CPLD is programmed through Verilog HDL language. The sick is determined according to the color change of test strips. Principle of color test circuit and design of software for identifying color data are also described. The software uses the principle of CIE Colorimetry to identify the color. Experiments show that test speed is fast and the result is precise. This system is suitable for the situations in which a large number of samples are to be treated.
Study on the technology of detecting and tracking an object based on the moon
Da-qian Wang, Yu-le Xiong, Zi Wang, et al.
The object-detecting and automatic image-tracking system based on the Moon is studied. This system utilizes a CCD image sensor, image processing technology and image tracking algorithm, can replace manual tracking of the moon without knowing the moving track of the moon in advance. While tracking the moon automatically, the system may record images of the moon, which is useful to record and process the surface data of the moon. Furthermore, it can be used to process the moon images, which is availed to analyze the moon images. The system is a useful attempt of a new method used to detect and track the Moon.
Quantification technology study on flaws in steam-filled pipelines based on image processing
Pei-xin Yuan, Jia-hui Cong, Bo Chen
Starting from exploiting the applied detection system of gas transmission pipeline, a set of X-ray image processing methods and pipeline flaw quantificational evaluation methods are proposed. Defective and non-defective strings and rows in gray image were extracted and oscillogram was obtained. We can distinguish defects in contrast with two gray images division. According to the gray value of defects with different thicknesses, the gray level depth curve is founded. Through exponential and polynomial fitting way to obtain the attenuation mathematical model which the beam penetrates pipeline, thus attain flaw deep dimension. This paper tests on the PPR pipe in the production of simulated holes flaw and cracks flaw. The X-ray source tube voltage was selected as 130kv and valve current was 1.5mA.Test results show that X-ray image processing methods, which meet the needs of high efficient flaw detection and provide quality safeguard for thick oil recovery, can be used successfully in detecting corrosion of insulated pipe.
Analysis of applying SBUVICCD to corona detection
Feng Yan, Huiying Song, Yuhuan Zhao, et al.
Using solar blind ultraviolet (SBUV) spectral light imaging technology to detect corona is a kind of advanced technology this time. Corona can be detected and imaged by using solar blind ultraviolet intensifier charge coupled device (SBUVICCD) without complex background to be processed. In this paper how to use ICCD to detect corona was analyzed. Imaging process of Gen II SBUVICCD was introduced and what will be noted during design instruments based on SBUVICCD to detect corona was also discussed. Some methods for deciding corona discharge level by using images from SBUVICCD were discussed sequentially. Finally, some corona pictures taken by using SBUVICCD were shown and expressed to support the items mentioned above. The result shows that SBUVICCD is suitable for corona detection in site.
Research on characteristics of forward scattering light based on Monte Carlo simulation
In ocean inspection, laser system has the advantages of high precision, high efficiency and being enacted on the temperature or salinity of seawater. It has been developed greatly in recent years. But it is not yet a mature inspection technique because of the complicacy of oceanic channel and water-scattering. There are many problems to be resolved. In this paper, the work principle and of general developing situation of ocean lidar techniques are introduced first. The author points out that the intense scattering and absorbing acting on light by water is the bottleneck to limit the development of ocean lidar. The Monet Carlo method is adopted finally to be a basal way of study in this paper after discussing several method of studying the light transmitting in seawater. Based on the theory of photon transmitted in the seawater and the particularity of underwater target detecting, we have studied the characters of laser scattering on underwater target surface and spatial and temporal characters of forward scattering. Starting from the particularity of underwater target detecting, a new model to describe the characters of laser scattering is presented. Based on this model, we developed the fast arithmetic, which enhanced the computation speed greatly and the precision was also assured. It made detecting real-time realizable. Basing on the Monte Carlo simulation and starting from the theory of photon transmitted in the seawater, we studied how the parameters of water quality and other systemic parameters affect the light forward scattering through seawater at spatial and temporal region and provided the theoretical sustentation of enhancing the SNR and operational distance.
Laser short-range detection system using digital processing
Because means of target detection is simple, laser short-range detection system using analog processing has high False- Alarm Rate. The requirement of target detection under complicated background can not be satisfied. Based on DSP and FPGA, this paper presents a mini laser short-range detection system using real-time digital processing. The modularized idea is applied to design the system. Every function module is designed respectively. The prototype is finally constituted, which provides algorithm of target identification and acquisition of echo data with hardware platform. The requirement of future application under strong clutter is satisfied.
The electrolytic polishing study of the stainless steel foil (SUS 304)
Yuqiong Li, Zhi-nong Yu, Wei Xue, et al.
Flexible flat panel display (FPD) is considered to be one of the most optimal and flourishing display technologies in the 21st century, and the processing and exploitation of flexible substrate is one of the key techniques of flexible display. Until now there have been three choices of flexible substrate materials: (1) ultra-thin glass; (2) polymer materials; (3) metal foils. The flexible substrates of electroluminescence display must endure high-temperature annealing from 400°C to 700°C for doping activation, and have good flexibility and can obstruct oxygen and water penetration. Based on above considerations, to adopt the stainless steel foil for the FPD is the most suitable. In this paper, the electrolytic polishing process of stainless steel foil is investigated, and the results of the experiment show that the polishing time, current density, distance of cathode and anode panel, and other technical parameters affect the electrolytic polishing process, and then induce the best technical parameters. The surface roughness of stainless steel sheet decreases from 0.12μm to 0.044μm, but the dongas appear after the steel surface being polished. The dongas patterns are investigated, and this provides a more scientific basis for the experiments in the future.
Image processing techniques for forward degenerate four-wave mixing experiment
Wei-Bo Wang, De-Ying Chen, Rong-Wei Fan
Degenerate four-wave mixing (DFWM) is a parametric process constrained by conversation of momentum of the incident and reflected photons, which imposes the condition of phase matching on the incident and generated signal beams. However, phase-match is not automatically achieved in the forward folded boxcars geometry. Also, weak signal beams under the strong background of stray light are hardly positioned and distinguished. To solve the problems, a new image processing system for detecting forward DFWM spectroscopy on iodine vapor is reported. This system is composed of CCD camera, imaging processing card and the related software. With the help of the detecting system, phase matching can be easily achieved in the optical arrangement by crossing the two pumps and the probe as diagonals linking opposite corners of a rectangular box. The signal is generated in the center of the box and propagates along the fourth diagonal, thus providing good spatial separation from the intense pump beams and providing a way to position the PhotoMultiplier Tube (PMT). Also it is practical to know the effect of the pointing stability on the optical path by monitoring facula changing with the laser beam pointing and disturbs of the environment. Finally Real-time detecting the rate of signal to noise so as to timely decrease the stray light with correct methods. Steady DFWM signals have been obtained in the experiment. This system makes it feasible that the potential application of FG-DFWM is used as a diagnostic tool in combustion research and environment monitoring.
Retrieval of terrestrial structural characteristics from satellite laser altimeter waveforms
Hui Zhou, Song Li
Satellite Laser Altimeter (SLA) mounts on a satellite, emitting a laser pulse that is reflected diffusely on the terrain, and partly return to the platform. The time of flight (TOF) of pulse and the emitter's position and orientation are used for determining terrain height. A new generation of laser altimeters additionally records the shape of the returning pulse. This recorded waveform carries information on the reflecting objects within the pulse diameter. Analysis of waveform is expected to retrieve terrestrial structural characteristics (e.g. slope, layer and reflectivity), besides terrain range. In this paper, a time dependent description of return pulse signal power is derived and terrestrial property is considered. By a nonlinear least square algorithm using suited initial parameter, the waveforms return pulse are modeled as a sum of Gaussian function. We show that terrestrial characteristics can be derived from parameters of Gaussian components - the centroid, width, area and number. The conclusion in this paper provides a theoretical foundation for retrieval of terrestrial structure.
The study of photoelectric detection technology for underwater projects
Gang Lu, Xiaohui Zhang, Donghua Zhu, et al.
The traditional methods to detect underwater objects are based on the acoustic detecting techniques. However, since the transmutation of the sound wave in ocean is often influenced by the oceanic boundary conditions and ambient factors such as salinity, temperature and pressure of the sea water, acoustic detecting techniques will cause large error in orientation and direction, which makes it difficult to capture and discriminate small objects. Instead, the photoelectric detection technology for underwater objects has the advantages of precise direction and orientation due to the high propagation velocity of light in water, consequently, the influence of ambient factors can be negligible. In this paper, we described the theory of underwater photoelectric detection and the system structure. Two kinds of experimental system are set up. One is imaging photoelectric detecting system; the other is non-imaging photoelectric detecting system. The underwater photoelectric detecting systems are made up of a short pulsed laser, a received optical system, narrowband optical filters, high-speed photoelectric detectors, a high-speed data acquisition and processing system etc. Both of the imaging and non-imaging photoelectric systems are employed to detect the reflection of target plane and simulated ship wakes. The key factors that affect the detection performance are analyzed in the paper. The experimental results show that for the imaging system, utilizing range-gated techniques can decrease the interference from background optical noise, while for the non-imaging system, using combining filters can suppress the backscattered optical noise from water. The conclusion is that both imaging and non-imaging photoelectric detection system are suitable for detecting underwater objects or their wakes.
Research on CO2 laser radar imaging experiment
The laser radar is a radar system adopting laser photosource and operating on optical band and the laser heterodyne measurement is a detection technique with high sensitivity. Optical system plays an important role in heterodyne detection system. The reasonable selection of performance parameters of optical system has direct influence upon the ability of system to detect objects. The characteristics of the receiver and the transmitter are discussed in this paper. In order to make the diffraction disk matching the detector size, the laser beam are confined and made the beam divergence angle of the transmitter equal to the receiver angle determined by antenna theory. In order to transmit laser to target's surface and receive the echo from the target efficiently, each optical parameter of the detective system must accord with the coherent condition. The CO2 laser coherent imaging radar system established by us can get the photo-quality imaging of the target and it has wide application foreground. Primary parameters including beam expander's clear aperture, beam divergence angle, the focus of system etc and calculating examples were given to show how to determine the parameter of optical system and realize these purposes.
Studying of the temporal characteristics of THz from photoconductor switches
Wei Shi, Ke Wang
We have studied the temporal characteristics of terahertz radiation generated by a biased photoconductor antennas triggered by an ultra-short optical pulse. The calculations are based on the current surge model of carrier transport in semiconductors. In our model, we include screening of the bias field by the space charge induced by carrier transport and by the generated terahertz radiation in the model, describing the electromagnetic radiation from a large aperture photoconductor. The surface current density affected by screening, the influence of the exciting optical pulse, time-dependent surface conductivity and time-dependent mobility are also taken into account in the model to describe the electromagnetic radiation from photoconductor antennas. Use these expressions the effect of the optical influence, the surface current density and time-dependent conductivity and mobility have been discussed in detail. The results show that new calculation model is more suitable for photoconductor antennas.
Carrier dynamics and terahertz radiation in large-aperture photoconductive antenna
Wei Shi, Xiao Fang Sun, Jun Zeng, et al.
The Drude-Lorentz theory was used to calculate carrier transport in semi-insulating semiconductors when the biased band-engineered heterostructures photoconductive antennas with very short lifetimes radiating terahertz. But the conventional Drude-Lorentz theory was suitable for the small dipole aperture antennas, the calculations results indicated that when a biased photoconductive antenna is pumped by femtosecond laser pulses to generate THz radiation, a major portion of the THz radiation is due to the ultrafast change of the carrier density. So the new calculation model of THz radiation from large-aperture photoconductive antennas was reported, which took into account the interaction between electrons and holes, trapping of carriers in mid-gap states, scattering of carriers, dynamical space-charge effects, radiation field screening effect and gave a melioration of the calculation of carrier' density. Several simulation results and analysis of the effects of different factors of THz radiation based on new calculation results were shown, by which the new calculation model was proved more suitable for large-aperture antennas.
Speckle reduction in laser projection display by modulating illumination light
The use of lasers in a projection display enables the creation of vibrant images with extensive color coverage. By adding a phase modulators in illumination systems and keeping the most part structures of the classic projection, speckle on the screen and retinas of the observers were restrained. The speckle's form and restraining were simulated. It was obtained form simulations that the contrasts of residual speckle on screen and on retinas are 0.0107 and 0.0132. The simulation proves that speckle on screen and on retinas can be suppressed by phase modulation of the illumination light in projection. It also indicated that the numerical aperture of projector affect the residual speckle on retinas. Experiments of speckle restraining were performed. It confirmed the results of the simulations.