2009 Vol. 30, No. 5

OE System and Engineering
Coaxial three-mirror-anastigmat system of high-resolution space camera
LI Xu-yang, LI Ying-cai, MA Zhen, YI Hong-wei
2009, 30(5): 717-723.
The problem that the primary mirror center is obscured by secondary mirror, existing in the reflective optical system, is researched for designing an optical system of the high-resolution space camera. Three optical systems of half, full and annular FOVs were proposed based on the analysis of the structural parameters of the coaxial three-mirror-anastigmat system and the distribution of the final FOV on the image plane. The coaxial three-mirroranastigmat systems of three modes, whose focal length is 3000 mm and F number is 10, are designed. The result indicates that the image quality of the three optical systems approaches the diffraction limit in the effective field, and can meet the different demand of high-resolution space camera. It is pointed out that the coaxial three-mirror-anastigmat system with half FOV is suitable to the push-broom imaging of linear array CCD, the coaxial three-mirror-anastigmat system with full FOV can be used to the staring imaging of planar array CCD, and the coaxial three-mirror-anastigmat system with annular FOV can realize the full color and multispectral imaging on a same camera.
Hardware algorithm based on liquid crystal partial gating image system
LI Qing, TANG Yuan-he, LIU Kai, GAO Hai-yang, ZHANG Rui-xia, ZHAO Gao-xiang, YE Na, LIANG Yuan, YANG Xu-dong
2009, 30(5): 724-729.
Since the CCD camera produces the halo while highlight is shining on it, the pixels on the CCD sensitive plane interacts on each other, and then the image blur follows next, an image improvement algorithm for overcoming the phenomenon of the halo is proposed. With the characteristic that the HTPS liquid crystal could perform the real-time control of the light transmissibility of each pixels, the pixels on the liquid crystal and main CCD are coupled one by one by optical fiber tapers. The image information gathered by a photometric CCD is processed by Cyclone II (core of the image processing unit). The liquid crystal is controlled by Cyclone II for improving the image quality. The PAL signal is gathered by the video capture chip. The Y channel gray scale information can be adjusted by the empirical formula and the output signal is transformed to VGA format. The experiment indicates that this system can precisely control the light transmissibility of each pixel on HTPS liquid crystal, entrusts the CCD camera with the ability to image normally under the highlight, and increases the resolution of the camera by a factor of two.
Vector angle compensating algorithm for panoramic rotating image
JIANG Tao, CHEN Fang-bin, WANG Xiao-qi, CHENG Gang, XING Jun-zhi, WANG Hong-hong, LIU Xiao-qiang, HU Bo
2009, 30(5): 730-733.
The direction vector of vertical axis of focal plane reference frame and analytical expression in cosine of a vector included angle measured from normal line for catoptric plane of a suppositional horizon outgoing plane were derived based on the five degrees of freedom analytical expression for a image line projected on focal plane to track the targets on sea surface by the panoramic photoelectric detecting system with both azimuth and pitching axes under the condition of threeframe disturbances and panoramic rotating image. The angle included between the direction vector of vertical axis of focal plane reference frame and the normal line of a suppositional horizon outgoing plane, which is less than /2, was acquired by subtracting /2 from arc cosine. The value from included angle multiplying 0.5 is taken as the static momentum of pitching reflector, which is a kernel of pitching position tracking algorithm adapting to arbitrary rotating angle for image line. In combination with the azimuth compensating algorithm (nondissertated in this paper), the tracking algorithm can make the image points of offshore targets to approximate to the original point of the focal plane from the beginning to the end. Simulation results and engineering test validate the algorithm.
Modeling of wire electrical discharge machining processobject based on neural network
SU Jun, WANG Bin
2009, 30(5): 734-746.
This paper establishes a prediction model which reveals the relationship between machining parameters and the process object of wire electrical discharge machining using BP neural network method. Input of the BP network includes pulse width, pulse interval, peak current, servo voltage, workpiece thickness, and output includes machining efficiency, surface roughness. The network is trained by the samples to realize the prediction of process object. The results show that the model reflects the principle of machining process of the machine tool, realizes the prediction of the machining efficiency and surface roughness under specific conditions, and the maximum predictive error is less than 10%.
Rigorous coupled-wave method for diffraction efficiency calculation of blazed gratings
CHEN Wei, LIAO Sheng
2009, 30(5): 734-738.
A rigorous coupled-wave (RCW) method, which adopts scattering matrix to calculate the diffraction efficiency of blazed gratings, is proposed to point against the low-accuracy of general scalar approximate algorithm. The calculation of diffraction accuracy was fulfilled by establishing a thorough theoretical model of blazed gratings and solving each harmonic coefficient with scattering matrix. The method has been used for calculating the diffraction accuracy of both TE and TM modes and solving the problem caused by numerical instability. The scalar method based on Beckmann-equation is provided for comparison.
Analysis of coupling between plasma and dielectric waveguides based on DFT method
WANG Xiao-long, ZHANG Bo
2009, 30(5): 739-742.
The properties of the coupling between two-dimensional dielectric slab and plasma waveguides are investigated with finite difference time domain methods based on the Fullwave module of Rsoft software. The coupling structure was simulated with the software and the coupling efficiency of light transmitting in the dielectric slab and plasma waveguides was calculated automatically the coupling, and then the variation curves of the coupling efficiency with the waveguide dimension and the wavelength of the light were drawn out. It is found that the gap width of MDM waveguide structure is related to the quality of the optical communication, and that the optimal point of the dielectric slab and plasma waveguides are all set at 15 nm according to the variation law of the coupling efficiency obtained by analysis. The coupling efficiency can be increased by 83% after further waveguide optimization of the geometric construction parameters.
Removal of strong arc interference in detection of V-shape weld based on path tracking under water
HE Yin-shui, ZHOU Guo-fa, ZHANG Hua, JIANG Jun
2009, 30(5): 747-750.
The algorithm of threshold automatic selection based on fuzzy reasoning for image processing of arc-v-shape weld seam is introduced. The removal method of the strong arc interference is proposed based on path tracking. By designing nine kinds of window templates, and acquiring the maximum average gray value in the region where these templates can cover through column scanning mode to get the vertical positions where the average gray value are maximum, the threshold is obtained through fuzzy reasoning using the maximum gray value and its increment. After that, all of the positions are tracked to find the white spots below the lowest one and above the tiptop one, and then eliminate the disturbances formed by blebs or little strong arcs below the lowest position and upon the tiptop.
Adjustment method for quasi zero optical path difference of VISAR
QI Wen-bo, YAN Ya-dong, CHEN Liang-yi, HE Jun-hua
2009, 30(5): 751-755.
The quasi zero optical path difference (OPD) that Mach-Zehnder interferometer must meet is introduced. The scheme that the rough adjustment to the interferometer is performed with laser first, and then the fine adjustment to it is carried out with white light is provided for realizing the precision adjustment for OPD, according to the characteristics that the white light has high accuracy for adjusting OPD but is not easy to be cohered. The alignment principle, accuracy and indeterminacy of OPD for the coarse adjustment of Mach-Zehnder interferometer with laser is analyzed in detail. An improved laser coarse adjustment scheme is put forward to overcome the indeterminacy of OPD, which raises the order of magnitude of OPD accuracy from millimeter to micron, dwindles the dead zone of the white light fine adjustment greatly, and made the white light fine adjustment simple and feasible. The adjustment accuracy of final OPD for the interferometer is 1.6m.
OE Information Acquisition and Processing
Synchronous image acquisition and processing system of multiple cameras based on source trigger and software control
JIANG Guang-wen, CHAO Zhi-chao, JIANG He-ping, FU Si-hua
2009, 30(5): 756-760.
Principle and method of synchronization were studied in hardware and software. One synchronous image acquisition and processing system was designed and implemented. A general digital output module was adopted as a synchronous trigger signal generator and controlled by computer program. The control program was developed in Visual C++ platform, which could adjust the image acquisition frame rate and trigger level of the cameras according to the cycle and waveform of trigger signals. Software synchronous strategy was designed to ensure the synchronous frames of every camera to be processed synchronously. The image acquisition system is easy to operate, low cost and can be accurately synchronized to less than 10s. The system avoided frame loss and mismatch, and provided a common solution for synchronization between multiple cameras.
Control method of adaptive fuzzy and PI forphotoelectric stabilization based on real-time OS
HONG Hua-jie, YUN Ping-ping, ZHAO Chuang-she
2009, 30(5): 761-767.
The stabilization control technology is one of the core technologies of the photoelectric stabilizing and aiming products. It is difficult for classical control theory to deal with the conflict between the overshot and rapidity, and to get satisfied dynamic performance. The system mathematical model was set up, and an adaptive fuzzy and PI compound controller was designed, which was realized on a digital platform based on the VxWorks OS. The simulation and experiment show that the system can realize the goals of zero overshot and rapidity with the designed controller. The system bandwidth was enhanced, which would favor the improvement of stabilization accuracy. The research provided a new stabilization control method for congeneric products.
Automatic segmentation algorithm based onspatio-temporal domain for video objects
CHENG Shu-hong, HU Chun-hai
2009, 30(5): 768-771.
A segmentation method to separate the moving objects from their backgrounds in a video sequence is proposed. Firstly, the global motion estimation and compensation is performed. Secondly, the continuous twice difference for the adjacent frames in the video sequence is implemented and the noise is filtered out with the adaptive filtering, and then the morphologic treatment is carried out. Thirdly, the effect of uncovered and covered background is eliminated with the difference intersection technology. At last, the mask matching and updating enables the algorithm to handle both quickly changing objects and temporary stop moving objects. Experimental results indicate that the moving objects can be automaticly extracted from the video sequence by the method and it has the strong robustness.
Application of adaptive digital filter in airborne weapon test system
FAN Hui-lin, HOU Man-yi, XUE Shan, XU Hong-ji
2009, 30(5): 772-776.
Aiming at the characteristics and test requirements of airborne weapons, the transverse adaptive digital filter (ADF) was built with least mean-square error (LMS) algorithm based on the analysis of ADF structure and optimization evaluation, and according to the design process of field programmable gate array (FPGA). The simulation result and application show that the ADF can realize the automatic adjustment of the weight coefficient vector and adapt to the characteristics of signals by creating 512kB random-access memory (RAM) space in FPGA. Since the LMS algorithm can get the best result in 0.1ms, the ADF designed in this paper can satisfy the test system of airborne weapons and the signal test error is less than 5%.
Application of optical correlator in automatic target recognition
ZHANG Yong, JIN Wei-qi
2009, 30(5): 777-782.
The joint transform correlator and Vander Lugt correlator applied in automatic target recognition are introduced in order to allow the optical correlation system to achieve a better application and guarantee the excellent recognizing effectiveness in automatic target recognition field under high-speed condition. Aiming at the key technologies in the realization process of the matched-filter correlator, the establishment of equal correlation peak synthetic discriminant functions to solve the problem appearing in the aberrance invariability recognition is brought forward. Furthermore, BP artificial neural net to recognize the correlation peak in correlation plane is put forward to solve the deficiency of threshold method in the correlation peak recognition technique. The nerve cell number of input layer is reduced and the ANN structure is simplified by dividing the interesting regions. The optical correlation system built in the lab proves the method can classify the correlation peaks from noises effectively and can improve the reliability remarkably.
Application of Fourier-Mellin transformation (FMT) in distortion-invariant image recognition
Lü Zhan-wei, DENG Chuan-jia
2009, 30(5): 783-786.
Fourier-Mellin transformation (FMT) was added in the optical joint transform correlator (JTC) recognition of the rotating and rescaling targets to overcome the low recognition ratio. The log?polar transformation, Mellin transformation and Fourier transformation used respectively in the FourierMellin Transformation (FMT), which has the invariance of rotation, scale and translation (RST), can eliminate the effect of distortion and improve the performance of image recognition. The simulation experiment of the correlation recognition for the targets with rotation angle of 0-40 and the dimension variation range of 0-20% was carried out with JTC. In comparison with the results of FMT, it is found that FMT added to JTC can realize the distortion-invariant image recognition.
Optical Metrology and Measurement
Course angle calibration of dynamic base with retro-reflector and CCD
YANG Yu-chuan, LUO Hui
2009, 30(5): 787-791.
Large range course angle measurement system of medium-to-high accuracy was studied for the course angle calibration of vehicle dynamic base. The system used two area array CCDs to identify the location of a reflected spot and realized the course angle measurement of dynamic base. To avoid the impact of base vibration, a retro-reflector was used. The system is optimized for airborne application because it is simple in structure and easy to adjust. An experimental setup was built based on the estimated parameters. After the signal detected by CCDs was processed by threshold segmentation, a center of gravity sub-pixel method was used to achieve position detection. The result shows that the accuracy of position measurement is about 0.4 pixel, the course angle is immune to the base vibration, and the accuracy of the measurement is better than 1 in the measurement range of 10.
Design of sun tracking system for FTIR monitoring of atmospheric composition
WANG Fang, LIU Jian-guo, GAO Min-guang, LU Fan, WANG Ya-ping, CHEN Jun, LIU Zhi-ming, JIN Ling
2009, 30(5): 792-796.
An atmospheric composition monitoring system, in which the sun-tracking and FTIR spectroscopy are combined, is introduced. The ATmega 128 chip is used as a controlling core of the tracking section of the system to realize real-time tracking of the sun in combination with the optics, electronics, GPS module, PSD position sensor and mechanical section. The spectral data gained by FTIR spectrometer and the computer is applied to the atmospheric composition monitoring. The system was verified by the experiments. The experiments show that the system is stable and reliable, and its tracking accuracy is within 0.3.
Shadow detection algorithm based movement feature
HAN Mei, JI Ming, SHI Zhi-fu, XIAO Jun, LIU Ya-qin
2009, 30(5): 797-801.
Shadowed area will appear in the displayed image when the field of view of a surveillance system is obscured, and it influences the analysis and further processing of the image. A real time shadow detection algorithm is presented to solve this problem. Firstly, the image is divided into image blocks based on inter-frame movement feature of sequence images in this algorithm. Secondly, the algorithm judges if this image frame is obscured and detects the possible shadowed area with the inter-frame predictor based on the gray mean of the image block. Finally, the shadow area is confirmed with a space domain filter for eliminating the erroneous detection areas. The experiment shows that this algorithm is real time and feasible.
Parallelism detection of optical axes for electro-optical system
SONG Yan-yan, WANG Ke-wei, HU Ling, ZHANG Ming, AN Jing, Xue Yong-gang
2009, 30(5): 802-805.
Several methods to detect the optical axes parallelism of multi-sensor electro-optical system were analyzed. The advantages and weakness of each method were compared. A practical method is proposed, which converts laser in infrared band to visible light detectable by CCD with an upconversion plate. A red spot was generated on the plate and retained for a while. The spot generated by the low frequency single pulse laser can be detected easily by a CCD. After some further processing, some parameters of the laser such as centroid and dimension can be measured and the parallelism between laser path and optical observation path can be detected.
LLL Night Vision Device and Imaging
Illumination-adjusting technology of light source used for image intensifier comprehensive testing
BAI Xiao-feng, SU Jun-hong, SHI Feng, HU Zheng-liang
2009, 30(5): 806-809.
In order to obtain the different output illuminance of the light source used for low-light-level image intensifier comprehensive testing, the traditional light source structure and its limitation were analyzed. According to the different illuminance needed in comprehensive testing, the large-scale continuous illuminance-adjusting function of light source was studied by analyzing and improving the traditional light source, based on the diffuse reflection characteristic of the integrating sphere and the continual characteristic of the micrometer. The output characteristic of the light source was specifically analyzed. The output illuminance of 2.510-5lx~680lx and the output light uniformity of 2.3% were achieved by testing in an experiment. It shows that the light source has a large illuminance range and higher output uniformity. Therefore, it can be used in testing the image intensifiers.
Microchannel plate with miniature channels
LE Wu-shi, CHEN Nan, LONG Gao-qun, MIAO Kun-zhi
2009, 30(5): 810-814.
The trend of miniaturization channel of MCP is introduced in the aspects of space resolution, time resolution and dynamic range. According to the relationship between MCP performance and structure, the problems such as distortion, crack, structure misplacemen of microchannel plate caused by the channel miniaturization are discussed, and solutions for the problems are analyzed. The analysis shows, according to the Omnibus I, II, III, IV programs formulated by United States Department of Defense, the developing sequence of MCP pore pitch is 12m, 10m, 9m, 8m, 6m and 5m. Some developed countries can even make the aperture of the microchannel plate 4m~5m and the resolution of the night vision system with tiny pore MCP more than 100lp/mm. The miniaturization of the channel is the trend of high performance MCP development. By improving the material composition, techniques of fiber-drawing, stick-arranging, billet fabrication and chemical treatment as well as equipments, manufacturing MCP with less than 5m pores can be achieved.
Optical Element and Fabrication
Preparation of strippable protection coating for lens
NIU Hui-qing, WANG Yue-feng
2009, 30(5): 815-817.
A new strippable film was developed to protect idle optical instruments from mildew,fogging and oil contamination. The new strippable protection film was made of polyvinyl chloride polymer(PVC) with antioxidant, inhibitor and other agents as ingredients. The performance of the coating was analyzed. The film-forming time was about 20min, the average mechanic strength was up to 4.52MPa. The film could be stripped easily. The environmental test results for antimildew and antifogging were very satisfactory, which proved the good performance of the protection film.
Computer controlled polishing for middle or small double-sided aspheric lens
MU Guang-yuan, FU Xiu-hua, SU Jia-ni, ZHANG Rui-zhi
2009, 30(5): 818-822.
Taking a dual aspheric convex lens with a diameter of 62mm as example, CNC grinding and polishing technology was investigated. A standard procedure of processing was presented to fast and-efficiently polish small and medium double-sided aspheric lens. Based on the computercontrolled optical surface molding technology, two-step polishing was used, which included full aperture polishing and smalltool corrective polishing. Surface form error was fed back iteratively for compensation during polishing process, and the surface form gradually converged to the required accuracy. The experimental results show that the final accuracy on both sides of the surface is less than 0.5m and the center deviation is less than 0.01mm, which fulfils the accuracy requirement of aspheric element in optical system. The technique handles the center deviation of the dual aspheric surfaces and the accuracy of the center thickness properly while ensuring excellent surface form accuracy and good surface polish.
Holographic grating made of two-wavelength water-resistant photopolymer
XU Xiang-min, ZHANG He-ling, LI Zhan-hua, SHAO Ji-bao, SHI Lei
2009, 30(5): 823-826.
The double-layer holographic grating made of a new kind of water-resisting photopolymer which is sensitive to the blue light of 488nm and red light of 632.8nm is introduced. Based on the experimental data and theoretical analysis, the characteristics of the material are investigated. The analysis shows that the resolution of this grating is above 5000line/mm and its diffraction efficiency is above 90%. The central wavelength drifting of the grating is nearly zero when temperature changes. The grating has many merits, such as one-step forming, low loss, etc. The doublelayer holographic grating is suitable for fabricating the wavelength-division multiplexer. The crosstalk question caused by the light coherence has been solved by the technology, and the crosstalk is smaller in comparison with the single-wavelength double-layer grating. During the production of the grating, two incident modes of beam can be chosen arbitrarily, which is oblique incidence and parallel incidence. It has the characteristics of wavelength selection and angle selection.
Fiber Sensing and Optical Communication
Application of FOG in table test
CHEN Yu-zhong, XIAO Hu, ZHANG Wei, HU Yong-ming
2009, 30(5): 827-830.
Fiber optic gyroscope (FOG) is a rate gyro suitable for table test at low angular rate. Based on the parameter of tables encoder, the data updating rate requirements of FOG at different angular rates and the influence of FOGs bias stability on measurement were analyzed. The table was tested at angular rate of 1/s by FOG. The frequency spectrum of the FOG output was analyzed and compared with oscilloscope measurement. The result showed the measurement of FOG was correct. The table was tested at angular rates between 0.05/s and 1/s by FOG. The test results show that FOG can be used for table test, and the angular rate fluctuation of table test at low angular rate can be measured by FOG. And the minimum angular rate of the test was given.
Gas concentration measurement based on fiber-circled cavity ring-down method
LI Wen-chao, SHA Xiao-peng, LIU Zheng-jun, LI Zhi-quan, FENG Lei, MA Bo-hua
2009, 30(5): 831-835.
In order to realize the trace gas concentration on-line measurement and analysis,a multi-type gas concentration on-line measurement system based on fiber-circled cavity ring-down method was designed and developed. Based on the nonlinear optical cavity ring-down technology, the experimental analysis of the gas concentration in-situ measurement with such system was performed. The gas-to-light absorption characteristics of the same gas with different concentrations changed with time and their relationship was given. The resolution of concentration measurement reaches 1ppb. The experiment proves that the system can be used to measure trace gas concentration effectively.
Fluorescence analysis of ytterbium-doped double-clad fiber laser
WANG Jian-guo, ZHENG Yi, DING Chun-feng, REN Huai-yuan
2009, 30(5): 836-839.
The luminescence accompanied in the visible region was found by experimental study of Yb3+ doped fiber laser. The spectrum of the green luminescence was measured with a spectrometer, which shows that the wavelengths of luminescence are 639.4nm, 520.7nm, 487nm and 474.8nm. Analysis shows that the concomitant red, green and blue luminescence is the result of the cooperation of Yb3+ and Pr3+. The fluorescence process is to transform the energy from Yb3+ ions to Pr3+, and exited Pr3+ induces red, green and blue luminescence. It is concluded from the experiment result that the luminescence produced after Yb3+ doped fiber laser absorbs pumped light is upconversion, which may degrade the transform efficiency of the laser energy of fiber lasers.
Infrared Technology
Consideration to radome technology for IR seeker
HUANG Qiu, CHEN Yi-qing, GAO Zhi-feng, ZHAI Xue-feng
2009, 30(5): 840-843.
The radome is one of the key components of infrared seekers. Especially for the missiles flighting in high speed, a lot of thermal stress is generated into the radome by rapid thermal shock, and the mechanical stress induced by the pneumatic pressure. In order to solve the problem of highspeed infrared seeker radome, material selection and radome design techniques are introduced. The factors which should be considered when the radome material is selected are analyzed according to the environmental requirements of high-speed infrared imaging seekers. It is found, by comparing the performance of the material parameters, that the spinel is the ideal radome material because of its good mechanical property, optical performance and easy preparation. The spinel was successfully applied for the high-speed IR seeker radome. A solution to reduce the aerodynamic heating effect of the radome by diamond film coating, signal processing and conformal design is proposed according to the analytical results of aerodynamic heating. The design principle and fabrication technology of conformal radome are introduced.
Un-cooled cold background infrared scene emitters
CHENG Juan, GAO Jiao-bo, YIN Tao
2009, 30(5): 844-848.
In order to meet the requirement of the high altitude infrared scene, the new physical concept is proposed and hardware-in-the-loop facility is developed for simulating the cold background infrared scene. The infrared scene with cold background(-30℃)was achieved at the room temperature(300K)by putting the initially transparent semiconductor screen made of Ge in front of the cryogenic system and by controlling its local radiation coefficient which is less then forbidden gap. The effect of cold background generated by liquid nitrogen and semiconductor cooler, the variation of radiation power with read-in luminous power, and the temperature contrast of cold background and target are tested. The result shows that the cold background produced by liquid nitrogen is -30℃ while semiconductor is 3℃, the conversion efficiency of the semiconductor is increased with enhancement of read-in luminous power, but the excessive read-in luminous power leads to the saturation of radiation power, temperature contrast is obviously increased while the read-in luminous power is enhanced.
Reflective electrically-addressed spatial light modulator based on infrared sheared stress polymer network liquid crystal
GAO Meng, GAO Jiao-bo, LUO Yan-ling, WANG Xue-wu
2009, 30(5): 849-852.
In order to supply the high frequency, wide spectrum, large dynamic infrared images for the semi-physical simulation test and evaluation system of the infrared-imaging seeker, the reflective electrically-addressed infrared spatial light modulator based on infrared sheared stress polymer network liquid crystal (SPNLC) was developed by making use of the electro-optical modulation mechanism of SPNLC, and a sample of electrically-addressed infrared SPNLC was fabricated. During the development, the control program was compiled by the aid of LabView, and the data register and control register were adopted to offer the read-in signal for the coding magnify circuit to drive every pixel. A reflective electrically-addressed infrared SPNLC spatial light modulator, whose thickness is 13m, was obtained by repetition test. The frame frequency of infrared images is 100Hz while the temperature of the blackbody is 300℃ and the driving voltage is 60V. The output maximum temperature difference is higher than 15℃.
Design of refractive/diffractive dual FOV optical system for uncooled LWIR thermal imager
BAI Yu, YANG Jian-feng, XUE Bin, RUAN Ping, MA Xiao-long, TIAN Hai-xia, WANG Nan-xi
2009, 30(5): 853-858.
Because of the large negative dispersive characteristic of diffractive optical elements, they are applied to infrared dual-FOV systems. The fundamental principle of chromatic aberration for diffractive optical elements is analyzed according to Fourier optics. The characteristic of refractive lens and diffractive optical lens is compared. A sample design of a optical system with zoom ratio 4∶1 which can be used in uncooled infrared thermal imager is presented. The manner of zoom is accomplished by exchanging two lenses into the wide FOV system configuration. The binary surface and aspheric surface is used to improve the image quality. The design result shows that when spatial frequency is 11lp/mm and the short focus is 40mm, the MTF value of each FOV is bigger then 0.6; when the long focus of 160mm, the MTF value of each FOV is bigger then 0.7; and both the wide-FOV and narrow-FOV have high image quality.
Laser Technology
Influence of partially coherent beam passing through strong turbulence on bit error rate of laser communication systems
WANG Jiang-an, ZHAO Ying-jun, WU Rong-hua, REN Xi-chuang
2009, 30(5): 859-863.
A theoretical base for using the technology of multibeam transmission and the reception in the ship laser communication systems was provided by the research on the influence of partially coherent beams passing through the strong turbulence on the bit error rate. The relation between system bit error rate and transmission range was obtained under the conditions of different turbulence measurement, transmission laser wavelength and light source coherence parameter by the aid of a method to parse the equation of laser transmission in atmospheric turbulence field, ignoring other noises in the system, but considering the bit error rate caused by atmospheric turbulence only. The result indicates that under the strong turbulence condition, the system bit error rate is increased gradually with the increase of the transmission range when the quantity of transmitting antennas reaches a certain number, but the system bit error rate tends to saturation when the transmission range accretion reaches a definite degree; the bigger the light source coherence parameter increases, the lower the system bit error rate becomes; the more the turbulence inner scale is, the higher the system bit error rate becomes; and the variation of the transmission laser wavelength has no obvious influence on the system bit error rate.
Laser transmittance measurement technology on plume from solid-propellant engine
CHEN Sheng-shi, NING Zi-li, OU Qiu-ye, CHEN Wen-sheng, JI Ming, GAO Jiao-bo, XUE Chang-jia
2009, 30(5): 864-868.
The main performance of hyper-velocity kinetic missile and its solid propellants is described. The mechanism of laser attenuation caused by the plume of solid rocket motor is analyzed. The plume transmittance of two solid-propellant formulations was tested by the aid of a smoke-box when the laser wavebands were 1.06m and 10.6m. The plume transmittance in 1.06m laser was tested with 1.064m laser modulation emitting, receiving and data acqui-sition system. The plume transmittance of 10.6m laser was derived after the optical transmittance of 2m ~13m laser was tested with the blackbody radiation source, spectroradiometer and data acquisition system. The tested data indicates that formulation 2 is better than formulation 1, and the plume transmittance 96%~97% of 10.6m laser is higher than that 92%~93% of 1.06m laser.
Threshold study of stimulated Brillouin scattering in water
SHI Jiu-lin, HE Xing-dao, LIU Juan, LI Shu-jing, ZHAO Xi-sheng, GUO Zhi-jun
2009, 30(5): 869-873.
In order to solve the insufficiency in the traditional definition for SBS threshold, a new definition and a noval measuring technique are proposed. The transmission of beam with different energy was measured at different lengths of water, and the attenuation coefficient of laser beam with different pulse energy was tested. The SBS threshold under different conditions was confirmed based on the attenuation coefficient. It was found during the experiment that the SBS threshold under the ideal stable state and the ideal transient state is a constant, it is related only to the pump laser and medium attribute, but not to the medium length. To other cases, the relationship between SBS threshold and length will be studied through further experiment.
Internally frequency-doubled hectowatt-level Nd∶YAG/KTP green laser side-pumped by LD
ZHANG Hao-lei, CHEN Xiu-yan, LI Xiu, CHEN Hao-wei, REN Zhao-yu, BAI Jin-tao
2009, 30(5): 874-878.
In order to obtain hectowatt-level green laser pumped by laser diode, two-rod series and two-acousto-optic Q-switching Z-shaped resonator was designed. According to the beam transformation matrixes, the variation of the fundamental mode radius in the laser crystal with the diopter and the distribution of the intracavity light field in the tangential and sagittal planes near the frequency-doubled crystal were simulated and calculated. The ideal resonator parameters were successfully sifted out based on the simulation and calculation. On the basis of optimal resonator parameters, the 532nm green laser was acquired, whose highest average power was 174.1W, the pulse width was 160ns, the optical-optical conversion efficiency was 16.1%, and the beam quality factor was M2x=9.63 and M2y=9.78, when the total pumping power was 1080W and the repetition rate was 10kHz. The result shows that high-power and high-quality hecto-watt-level green laser can be obtained by two-rod modules and two-acousto-optic Q-switched Zshaped resonator configuration.
Determination of effective aperture and estimation of truncation energy in synchronous three-channel optical system for laser warning
MA Jian, LIU Bing-qi, HUA Wen-shen, MAN Bo, LUO Xin-xin
2009, 30(5): 879-884.
The model for laser irradiation transmission in far-field was established to determine optical system effective aperture and estimate truncation energy for a synchronous three-channel laser warning system. The numerical relation of far-field spot radius, single channel entrance radius and relative energy difference in different channels was stimulated. The results reveal that the relative energy difference in different channel is independent of the energy density in the far-field spot center, in which the maximum ratio is located at the spot rim. When the maximum relative energy difference is limited, the allowable single channel radius is increased with the farfield spot radius, but the truncation pulse energy or power is reduced. When the maximum relative energy difference is 1%, and the far-field spot radius is 2.5m,4.0m and 7.5m, the allowable single channel radius is 3mm, 5mm and 10mm,the biggest truncation pulse energy is 1.1410-5J 7.5410-6J 2.6810-6J,and the biggest truncation pulse power is 1.63W,1.08W and 0.38W.
Storage of Tiegun dioscorea opposita thunb by He-e laser irradiation
WEI Shan-cheng, XU An-tao, ZHANG Rui, rui, ZHAO Xi-ting, ZHOU Xiao-yan
2009, 30(5): 885-888.
The Lo bud germination inhibition of Tiegun dioscorea opposita thunb occurred, the yam stem water content, total soluble sugar and soluble protein content respectively declined from 70.2039% to 66.61544%, from 72.21325mgg-1 to 25.87888mgg-1 and from 508.5394gg-1 to 258.4231gg-1, and MDA and O2 contents respectively increased from 0.62mmolg-1 to 8.033122mmolg-1 and from 32.99713gg-1 to 35.53642gg-1 after it was irradiated by 2.5mW He-e laser for 30min. After the laser irradiation, the superoxide dismutase (SOD) activity of Tiegun dioscorea opposita thunb increased from 494.864Ug-1 to 1105.85Ug-1 in the initial period of its storage and then declined from 1105.85Ug-1 to 959.167Ug-1.