2016 Vol. 37, No. 3

Design and analysis of azimuth-gimbal in aerial opto-electronic stabilized platform
Tan Songnian, Li Quanchao, Zhang Hongwei, Li Lei
2016, 37(3): 327-331. doi: 10.5768/JAO201637.0301001
Image field rotation can occur during the process of nearinfrared camera vertical imaging in optoelectronic stabilized platform in helicopter. In order to eliminate the image field rotation and satisfy the requirements of carrier aircraft space size, the cantilever structure azimuthgimbal was introduced, and the threedimensional model of the azimuthgimbal was established. In order to analyze the rationality of the cantilever structure, the finite element model was established to carry out its static analysis and modal analysis separately. Results show that in load case of 24.5 kg, the maximum deformation is 0.025 4 mm, which meets the requirements of the pointing error distribution; and the first natural frequency is 42.99Hz, which meets the servo bandwidths requirements.
OE System and Engineering
Simulation of backlight imaging system by spherically bent crystal
Liu Lifeng, Xiao Shali, Qian Jiayu
2016, 37(3): 332-336. doi: 10.5768/JAO201637.0301002
Xray imaging system based on spherically bent crystal is an important diagnostic technique for inertial confinement fusion (ICF). To testify the performance of the imaging system and optimize the structure of imaging system, the backlighting imaging system was studied by the ray tracing software SHADOW. Through the analysis for the system parametes, such as the position of object, the radius and Bragg angle, the results showed that for the spherical surface crystal back light imaging systems with Bragg angle of 57 and 65 ,when the object thickness or object laying aside error was a=1 mm, the crystal bevelling radius error was R=3 mm, and the Bragg angle error =0.1 mrad, the relative magnification of the 2 imaging systems simulated on the meridian plane and the sagittal plane through light tracing ,tailled with the computation result by relative magnification formula comparison.It is implied that the parameters have a little influence on the relative magnification of the imaging system, and the performance of imaging system is stable and reliable.
Design and analysis for large aperture primary aluminum mirrors
Li Quanchao, Li Lei, Tan Songnian, Zhang Hongwei
2016, 37(3): 337-341. doi: 10.5768/JAO201637.0301003
Aiming at the aluminum alloy material,a largeaperture primary mirror of infrared camera was designed with the mirror aperture of 420 mm. Starting from the diameterthickness ratio, the number of the support points and the lightweight structural form, a structure of open back, triangle lightweight construction and back threepoint support was designed. Dynamic stiffness of the mirror and surface shape change under the weight and temperature loads were analyzed by the finite analysis software. The results show that the natural frequency of the mirror is enough, which has a sufficiently high dynamic stiffness. Both surface accuracy RMS of the mirror(30 nm,0.2 nm) have reached the index requirements of the optical system(/10,=632.8 nm) under gravity and a uniform temperature drop of -40℃,which provides a theoretical basis for the design of infrared aluminum mirror.
Design and realization of lowlightlevel nightvision device detection system based on machine vision
Jiang Heng, Wang Xiaobing, Zhang Jing, Zhu Baohui
2016, 37(3): 342-346. doi: 10.5768/JAO201637.0301004
A detection system of lowlightlevel nightvision device was designed and developed,which utilized the CCD component as the detection receiver of the output image.It can be used to test the image intensifier in lowlightlevel night vision system. The testing parameters of image intensifier performence in lowlightlevel night vision system were introduced, the comprehensive test method and principle for all the parameters were analyzed. Through the optimizing design of the architectural structure,optical system,CCD selection and testing software , it was realized that many performance parameters of image intensifier in lowlightlevel night vision system such as resolution ratio,brightness gain,brightness uniformity,brightness stability could be measured by single equipment. The experiments results show that the random measurement error is less than 3%.
Influence of vibration on transfer function of television imaging system
Dong Zaitian, Zhang Yijun, Tao Zhong, He Haifeng, Xi Weisheng, Liu Changliang
2016, 37(3): 347-352. doi: 10.5768/JAO201637.0301005
In order to study the transfer function of television imaging system affectted by vibration,the transfer functions under different vibrations were analyzed and compared, and through utilizing the energy integral method.And then the laws were measured and verificated by the fast mirror system and ISITE measurement system. Simulation and experiments results show that for the TV imaging system developed, when the frequency of vibration is lower than the exposure frequency,the downtrend of the transfer function can increase from 0.167 in static condition to 0.237 with the increasing frequency of vibration ; when the frequency of vibration is higher than the exposure frequency,the downtrend of the transfer function can fluctuate increasingly and gradually tends to 1.42 times that of the static condition.
Temperature field analysis and structure redesign of fiber optic gyroscopeWan Xun, Xie Liangping
Wan Xun, Xie Liangping
2016, 37(3): 353-358. doi: 10.5768/JAO201637.0301006
The thermal element model of fiber coil was built based on the discrete mathematics formulae of the Shupe error in the fiber optic gyroscope (FOG). The transient thermal behavior and the steadystate thermal behavior were analyzed by this element model. According to these results, the reasons how the asymmetrical temperature field have an impact on bias error were found. The optimized structure of FOG shell, which has an inner of magnetically soft alloy and a outer of ultralumin , was designed, based on the analysis and emulation of the temperature field to decrease temperature grads of coil. The optimized thickness of the inner is 0.8 mm. The optimized thickness of the outer is 1.5 mm. It can improve the thermal symmetry of the fiber ring. The temperature changes of coil decreases by 1.8 ℃, and the difference in temperature of coil decreases by 0.68 ℃ in the temperaturefall period by experiments. Compared with the results of the experimentation, we approved the redesigned structure which can improve the temperature distributing and reduce the temperature spatiotemporal change rate of FOG coil.
Design of zoom system for automatic focal length measurement on optical bench
Cai Jinhao, Yang Pengli, Ma Aiqiu, Feng Jie, Fu Xiaoqing, An Jing, Wang Zhi, Li Wenting
2016, 37(3): 359-364. doi: 10.5768/JAO201637.0301007
In order to improve the accuracy of automatic focal length measurement on the optical bench, a continuous zoom optical system was designed. The system is composed of selfcollimation component and zoom component, and can adjust the size of image on CCD target surface till the best measurement is got. According to the technical requirements of the zoom system and based on the total control, the initial structure selection and image quality optimization were done. After the completion of the design,the focal length of self collimation component is 200 mm,the zoom component is 200 mm~20 mm and the zoom system after docking can realize the image size of 1~10 of continuous adjustment. Simulation results show that the zoom system shows good image quality,the modulation transfer function (MTF) curve is close to the diffraction limit, and the dispersion spot is less than the size of CCD pixel. The above implies that actual testing requirements can be met.
OE Information Acquisition and Processing
Color image denoising using high order iterating model by combining relaxed median filter
Lu Bibo, Li Yang, Wang Yongmao
2016, 37(3): 365-371. doi: 10.5768/JAO201637.0302001
An improved iterating algorithm was proposed to eliminate the speckles preserved by the local curvaturebased model as geometrical characteristic. It utilized the local curvature coupling 3 channels as the regularizing term,then detected speckles by using local statistics values. The relaxed median filter was introduced to suppress these speckles. Numerical experiments using images of different features were carried out and the evolution of the values of the peak signal to noise ratio(PSNR) was analyzed. The results show that this algorithm can accelerate the progress of evolution and eliminate the speckles while protecting the image structure information. The value of the PSNR increases by 2.47%, and the iterations decrease by 93.66%.
Optimal design and implementation for online rail surface defects detection system
Liu Heng, Zhang Jun, Dai Guangyu, Lyu Kunlin, Chen Zhe
2016, 37(3): 372-379. doi: 10.5768/JAO201637.0302002
Under the premise for guaranteeing the accuracy of detection, combining with the characteristics of the rail surface image and the software engineering concepts, 3 optimization methods were presented for the issue of slower speed in rail surface defects detection, including the aspects of algorithm, programming technology and storage medium. According to redesign of the algorithm flow, the efficiency of the algorithm mapping to CPU was improved; the multithread programming was used to make full use of the multicore strengths of the CPU; the efficiency of the hardware was improved by using solid state drive (SSD) to read and write images, the SSD has the characteristics of fast reading and writing, light weight, low energy consumption and small size. The experiment results demonstrate that the average time consuming decreases from 17.94 ms to 8.33 ms per picture after optimization,the speed improves by 53.57%. That means the speed of train is about 207 km/h in 1 mm accuracy resolution and the system can satisfy the requirements of online detection of rail surface defects.
Humankind shape object detection using deformable parts model with HOG features
Song Jin, Wang Shifeng
2016, 37(3): 380-384. doi: 10.5768/JAO201637.0302003
It is one of the important tasks in machine vision field to detect specific object using single image. A machine learning approach using latent support vector machine(LSVM) classifier was presented for detecting humankind shape object. The histogram of oriented gradients(HOG) features were extracted and the corresponding deformable parts were formed to describe the appearance of the object. The problem that the objects appearance deformed when it was in motion, was solved. 200 images captured in typical public areas were randomly selected and used to perform this method. 1 100 humankind shape objects from them were tested, and the correct recognition rate of 78.3% was achieved. The experimental results show that this approach is able to detect humankind shapes and mark them out which demonstrate its feasibility and stability;however,misdetection can happen when the humankind shape object is partly covered.
Refueling drogue tracking based on trackinglearningdetection algorithm
Gao Yu, Kong Xingwei, Dong Xinmin, Wang Haitao, Wang Jian
2016, 37(3): 385-391. doi: 10.5768/JAO201637.0302004
To solve the drogue tracking problem during the capture phase of autonomous aerial refueling, a trackinglearningdetection (TLD) algorithm was proposed. The algorithm decomposes the drogue tracking task into 3 subtasks: tracking, learning and detection. The tracking component is based on the LucasKanade (LK) method extended with failure detection and chooses tracking points with good performance to track the refueling drogue; and the detector constructs cascaded classifier to sort the picture patches scanned by scanningwindow and returns patches containing object, which integrates with tracking component result and gives final tracking result; and then the PN constraints are introduced into the learning component to correct wrong samples and then learn and update the detector. A scene simulation for aerial refueling was developed based on Creator/Vega Prime. The experimental results of the test on the video of scene simulation show that the success rate of tracking drogue is 95.5%, the average time consumption is about 31.4 ms, and the algorithm can meet well requirements of drogue tracking, such as robustness, precision and real time performance.
Method for calibrating interferogram based on weighted least square
Yang Cheng, Han Sen, Wu Quanying
2016, 37(3): 392-396. doi: 10.5768/JAO201637.0302005
A new method depending on weighed least square was proposed, aiming at the shortcomings of the existing interferogram calibration method. It used the edge information differences between standard parts edges and fringes edges, then extracted the target edges by using appropriate mask, and finally used the weighed least square way to position the edge more exactly. The new method can figure out the real length of each pixel finally depending on the standard parts known size. The experiments show that this method costs half time than Hough transform, and the positioning accuracy is less than 1 pixel. It can calibrate each type of interferogram well with strong practicability.
Fluorescence spectrum denoising of quantum dots based on improved wavelet threshold
Chen Yu, Zhang Zhengping, Wang Jing, Chen Xiaopeng, Zhu Ziyang
2016, 37(3): 397-401. doi: 10.5768/JAO201637.0302006
The signal collected by using the spectrometer is inevitably affected by different noise sources. In order to increase the analytical accuracy of spectrum signal, an improved denoising method with threshold was presented by analyzing the principle of applying the wavelet to signal denoising and the defects existed in classical denoising methods by using soft and hard thresholds. The improved method can overcome both the defects,that the hard threshold method generates discontinuities and the soft threshold method generates a constant variation, and can retain the useful signals as much as possible. In experiment, the SymletsA wavelet was selected as the wavelet function with 4 series, through combining with the perlevel threshold determined by the BirgeMassart tactics pattern,the denoising process was conducted for the fluorescence spectrum signal of CdSe quantum dots . Simulation results demonstrate that the rebuilt signal by the improved denoising method with threshold can has a increased signaltonoise ratio(SNR=47.550 2) and a energy accounting(PER=0.973 3), as well as an improved mean squared error(MSE=149.421 3) compared with the classical denoising methods by using soft and hard thresholds.
Optical Metrology and Measurement
Method for defects detection and 3D reconstruction based on dispersed points cloud
Wang Ying, Wu Feng, Fu Guoping
2016, 37(3): 402-406. doi: 10.5768/JAO201637.0303001
Equipment surface defect detection is very important for ensuring safety production and avoiding economic losses. Aiming at the algorithm complexity problem of defect detection and 3D reconstruction for dispersed 3D points on the equipment surface, a new method was proposed. All the points were divided into different layers along to the axis, then the points on the layer were moved to the middle plane of the layer. The distribution of the points became regularly and the defect detection and 3D reconstruction were done by the points regularized. The dispersed points defects detection and 3D reconstructions were fulfilled and the error of the defection detection is 1.01%. Experimental results show that this defection detection method proposed is simple and easy to implement after the dispersed points are regularized.
Technical progress and analysis on largescale spatial angle measurement
Chen Zhinbin, Xiao Wenjian, Ma Dongxi, Liu Xianhong, Xiao Cheng, Qin Mengze
2016, 37(3): 407-414. doi: 10.5768/JAO201637.0303002
With the rapid development of large equipment manufacturing industry, the manufacture and assembly processes have increasingly higher demands on largescale spatial geometric quantity measurement. In order to analyze the development of angle measurement technology in largescale spatial geometric quantity measurement, 5 traditional methods were reviewed, and 3 new related research achievements about angle measurements were introduced. Then combining the optical selfcollimation tracking technology and inertial measurement technology, a novel largescale spatial angle measurement method based on inertial reference was elaborated. The method can perform portability, versatility and strong antiinterference ability and it is very suitable for field measurement. Test results show that the current measurement range is 10 m and the measurement accuracy is 0.5 .Additional the improving schemes for the measurement range and accuracy were put forward.
PSD nonlinear correction based on BP optimization algorithm
Zhang Xinting, Kang Lei, Wu Qianqian, Zhang Wanyi, Li Yuyao
2016, 37(3): 415-418. doi: 10.5768/JAO201637.0303003
For the inherent nonlinearity of position sensitive detector (PSD),a PSD nonlinear correction method based on backpropagation (BP) optimization algorithm was proposed.Based on the traditional Newton algorithm , the relevant principle of LevenbergMarquardt algorithm was deduced, that is the BP optimization algorithm.The Matlab software was used for programming, the network utilized the structure having 2 hidden layers,and the numbers of neurons for them were 40 and 30,respectively,the max training time was 500,and finally the results were computed by sim function and outputed through simulated network.Through verified by experiment, the network output error is almost within 0.001 mm, of which the maximum error is less than 0.003 mm, achieving the PSD nonlinear correction.
Optimization method of straightness error based on video measuring machine
Jing Min
2016, 37(3): 419-424. doi: 10.5768/JAO201637.0303004
According to the characteristics of the video measuring machine, the optimization of straightness error measuring was introduced. A method to evaluate straightness error with intervaldistance improved algorithm which conforms to minimum zone condition was proposed and the improved edge detection template was designed. Using the method of image measurement experiment of smooth limit gauge, comparing with the traditional edge detection method and gradient search method, a system for measuring straightness error was tested. Experiment results show that the improved edge detection algorithm can improve the measurement speed, the calculation convolution time is reduced by half comparing with the traditional testing templates.The intervaldistance improved algorithm was compared with the gradient searching algorithm, and results show that the relative error of straightness error for the same 8 groups of data is less than 2%, the average computation speed is increased by 0.01 s. It is verified that the computation time can be saved by 4.45 s with the optimized method in the experiment for measuring straightness error of different diameter gauges by imaging instrument . Through different ways of evaluation, the best span for measuring straightness error of 0.078 mm~0.104 mm was advized,which can provide a foundation for realtime detection.
Retrieving aerosol mass concentration vertical distribution in north suburb area of Nanjing city
Shen Fuzhen, Guo Shengli, Zhang Wei, Cao Nianwen, Tian Li
2016, 37(3): 425-429. doi: 10.5768/JAO201637.0303005
Routine tests were conducted by using RamanMie lidar in the northern suburb of Nanjing.Through the analysis of the lidar echo sinal,aerosol mass concentration profile was inversed with the aid of aerosol mass concentration of linear model and exponential model.In order to improve the accuracy of the inversion,first of all,the Mie scattering signal near field was corrected,eliminating the influence of overlap factor.And denoising methods were used to deal with Raman scattering signal such as wavelet analysis.Secondly the Mie scattering signal was used to inverse the 0~3 km atmospheric aerosol mass concentration,the Raman scattering signal was used to inverse the 3 km~10 km atmospheric aerosol mass concentration,and then the two signals were spliced.Experimental results show that the correlation coefficient of aerosol mass concentration in different time is 0.991 and 0.973 6 inversed with two kinds of models, which is reliable.
Spot location algorithm of weapon automata motion testing system
hang Jing, Liu Ji, Liu Xiu, Zhang Bin, Li Shiwei
2016, 37(3): 430-434. doi: 10.5768/JAO201637.0303006
Aiming at the problems of bad antiinterference capacity and low localization accuracy in traditional localization algorithms of spot center which include the center of gravity method, the Gaussian fitting and so on, we raised a improving way which calculates the center of spot on the basis of the circle fitting method. Using the type of 56 submachine gun, we conducted the single shot experiment and processed the data obtained by testing system through the modified circle fitting, Gaussian fitting, and gravity method, respectively. Compared with the testing result of OFV5000 laser velocimeter,the relative error of improved circle fitting is only 0.92%. The result shows that the algorithm improves the antiinterference ability and achieves the rapid and accurate calculation of spot center,and obtains the weapons motion parameters.
Optical Element and Fabrication
Optical design of 3 independent freeform surface LEDs automotive dipped headlamp
Yao Hongbing, Wang Dandan, Xin Zhonghua, Xu Jin, Liu Min
2016, 37(3): 435-440. doi: 10.5768/JAO201637.0305001
In order to make sure of adequate lighting for the driver of the vehicle, and prevent the opposite driver from glare, an automotive dipped headlamp system with a cutoff line was designed. A dipped headlamp according to GB259912010 light distribution standard (automotive headlamps with LED light sources/or LED modules) was designed with highpower LED and free form reflectors (FFRs) which had simple structure and high optical efficiency. Based on the nonimaging optics theory, the correspondence between the angle of the light reflected by the freeform reflector and the coordinates of point in the target plane was established. The freeform lens point coordinates were calculated according to the correspondence of reflection and refraction laws. To achieve light distribution requirement, the fundamental surfaces were divided legitimately and the surface profile data of subsurfaces were optimized and adjusted. The function of dipped headlamp was realized by 3 LEDs, each of which had its own independent optical system. The test results show that the optical system has a clear cutoff line, with the efficiency reaching 54%, which can fully meet the requirements of the illumination of regulation on each test point.
Design of ultra wideangle photographic objective based on ZEMAX
Hou Guozhu, Lyu Lijun
2016, 37(3): 441-445. doi: 10.5768/JAO201637.0305002
For the problem about the design of ultra wideangle photographic objective,an ultra wideangle photographic objective was designed with ZEMAX optical software. The design was carried out by limiting the basic parameters and dimensions of lens with various operations and by selecting the appropriate rear group. The former group structure was designed by using the three inverse Galileo systems. The former group and the rear group were mixed together and the overall initial structure was further optimizd. The optical system is composed of 16 pieces of spherical lenses applicable within the visible light region. The main optical parameters are as follows:the focal length is 6.2 mm,the full field of view(FOV) is 100,the F number is 2.1. From the result we can see that the absolute value of maximum distortion of FOV lens is less than 3.5%,the maximum field curve is less than 0.05 mm,the modulation transfer function (MTF) of the whole field of view at 50 lp/mm is greater than 0.7,approaching to the diffraction limit.
Design and simulation of circle module for edge LED backlight
Zhou Yingchu, Guo Kangxian, Xiao Bo
2016, 37(3): 446-451. doi: 10.5768/JAO201637.0305003
The light guide plate (LGP) with side lighting is effective to reduce the thickness of the display module and the number of the LEDlights. In order to obtain uniform surface illumination, a circle structure of light guide plate was introduced. Through deriving the rule of scattering netted dots, the distribution function for the size of scattering netted dots in light guide plate was obtained . Using VBA program, the scattering netted dots were generated in the CAD. Combined with the simulation software, it is verified that the luminance uniformity is more than 90% in the display area of guide plate, which meets the design requirements of back light module project.
Design and application of MEMS optical switch array
Zhao Lei, Wang Xiaoqi, Li Jingdi, Zhao Zhenhai, Liu Huabo, Ma Youheng
2016, 37(3): 452-455. doi: 10.5768/JAO201637.0305004
For the problem of reducing the response time in air defense missile system, a micro electro mechanical system (MEMS) optical switch array was designed to control the signal transmission of subsystems in air defense missile system. The optical switch array which was constituted by 8 group double layer electrostatic comb structures,was used to control the On and Off state in every single subsystem. According to the LagrangeMaxwell equation, the electromechanical dynamics model was established, and the main parameters were confirmed including the mass, the elastic, the capacitance, the airfilm damp and so on. Then the parameters with genetic algorithm were optimized. The simulation result shows that the response time equals 0.627 ms, the steadystate displacement equals 4.724 m, the maximal displacement equals 6.801 m, the response time is one fourth of the original time. The result indicates that the MEMS optical switch array plays a role not only in reducing the response time, but also in ensuring the stability in air defense missile system.
Infrared Technology
Design of cold MWIR/LWIR infrared dualband/dualfield panoramic optical system
Liu Jun, Zhang Xibin, Gao Ming
2016, 37(3): 456-464. doi: 10.5768/JAO201637.0306001
In order to identify that two bands information of the medium wavelength infrared radiation (MWIR) and the long wavelength infrared radiation(LWIR), realize the fast switch of two different fields of view(FOV), and further enhance the efficiency and range of existing systems to detect, a fourchannel cooled infrared dualband dualfield panoramic imaging optical system was designed by using the method of spatial multicamera image mosaic panoramic imaging. The panoramic system is consisted of three infrared lenses with mutual intersection angle of 120 in circularviewing direction and one infrared lens in top view direction, each optical system of imaging channel is designed to be the double imaging configuration.The Fnumber is 2, the working band is MWIR 3.5 m~4.8 m and LWIR 7.8 m~9.8 m, the full field of view(FOV) is 122 , the ratio of long focal length to short focal length is 5, and it can complete 122 /44.49 dualfield transformation through the moving of the zoom configuration in axial direction. By adopting the refractive /diffractive hybrid optical elements and introducing aspheric design technique, the system was made temperature compensation by the means of optical passive athermalization. The result indicates that the system has almost 100% efficiency of the cold stop and a good ability of narcissus restraining. At the Nyquist frequency of 18 lp/mm, the modulation transfer function (MTF) values of LWIR optical system are all greater than 0.3 , and that of MWIR are all greater than 0.5.The image plane is stable and the image quality is excellent when the system works on -40 ℃ ~ + 60 ℃.
Design of 10× infrared zoom lens with all sphere surfaces
Zhao Yingming, Yang Ruofu, Yang Chunping
2016, 37(3): 465-470. doi: 10.5768/JAO201637.0306002
For the 320240 pixels uncooled infrared focal plane array(FPA) detector, a midinfrared zoom optical system was designed working at 3.7 m~4.8 m waveband.It contains 6 sphere lenses. All lens elements are made up of silicon and germanium materials which can transmit 3.7 m~4.8 m infrared rays. The F number is 2.5, the back working length is 20 mm, and it can realize 15 mm~150 mm continuous zoom. Designed results show that the modulation transfer function (MTF) value of zoom lens is greater than 0.6 at 16 lp/mm in the full field of view (FOV), and no less than 0.7 in the 0.7 FOV,which means near the diffraction limit generally. The uncooled infrared unit for plane arrays can catch more than 70% infrared rays energy. The lens system is characterized by small F number, long back work length and all spherical surfaces. And the image quality meets the requirements within -20 ℃~60 ℃.
Study on optical limiting effect of graphene in midinfrared band
Zhang Zenan, Bai Yang, Bai Bing, Li Weilong, Feng Xiaoqiang
2016, 37(3): 471-475. doi: 10.5768/JAO201637.0306003
The optical limiting effect of the graphene films in midinfrared band (3 m~5 m) was studied using nanosecond pulsed laser Zscan method . The Zscan curve obtained from the open aperture experiment showed a single valley structure, but the same structure did not show in the closedaperture Zscan curve. Through the fitting and calculation of the openaperture Zscan curve, the 3order nonlinear absorption coefficients and the optical limiting thresholds of 3 layers graphene were 11.3910-7cm/W, 10.6110-7cm/W, 9.7510-7cm/W, 8.8110-7 cm/W and 3.49 J/cm2, 3.75 J/cm2, 4.11 J/cm2, 4.55 J/cm2 at 3.010 m, 3.522 m, 4.326 m and 4.880 4 m, respectively. The 3order nonlinear absorption coefficients and the optical limiting thresholds of 3 layers, 5 layers and 7 layers graphene in 3.522 m center wavelength were 10.6110-7cm/W, 11.3210-7cm/W, 11.9510-7cm/W and 3.75 J/cm2,3.41 J/cm2,3.32 J/cm2, respectively. The experimental results show the optical limiting effect of graphene is obvious in the midinfrared band based on nonlinear reverse saturable absorption.
Laser Technology
Analysis on laser comprehensive application systems
Yang Aifen, Li Gang, Wang Liang, Zhang Biao, Zhang Jia, Li Longxiang
2016, 37(3): 476-481. doi: 10.5768/JAO201637.0307001
The basic concept and realization thought of laser comprehensive applications are introduced in order to improve the overall performance and optimize the design of weapon platforms.Laser comprehensive application systems are classifed into 3 types according to different lasers used.The first type is pulse solidstate lasers with peak power of MW to hundreds MW.The prototype with 2 J pulse energy has been developed.The second type is high frequency lasers with peak power of hundreds W to thousands W.The third type is pulse semiconductor lasers with average power of mW to W.These 3 multifunction laser comprehensive application systems will play an important role in future new weapon platforms,and it will necessarily promote the total performance of series of future new weapon platforms tremendously.
Measurement of highvelocity gas flow parameters using laser Brillouin scattering
Zhang Xiaohong
2016, 37(3): 482-488. doi: 10.5768/JAO201637.0307002
Laser Brillouin scattering is the result of the inelastic light scattering from the medium density fluctuations. The shape of the Brillouin scattering spectrum is dependent on the gas pressure, temperature, and the scattering angle. An effective nonintrusive method for measuring the temperature and pressure in gas flow was provided. The measurement principle of the highvelocity gas flow parameters by using laser Brillouin scattering was reviewed. A measurement device based on the FabryPerot interferometer (FPI) was designed to measure the RayleighBrillouin spectrum of the gas flow, and the laser Brillouin scattering spectrum was obtained for a N2 gas flow. Experimental results show that the error of the pressure and temperature derived from the Brillouin scattering spectrum is less than 15% compared with the theory model.
Thermal effect of variable thermalconductivity square Yb∶YAG crystal endpumped by pulse LD
Geng Yingge, Li Long, Pan Xiaorui, Fu Yiliu, Gao Dangli
2016, 37(3): 489-494. doi: 10.5768/JAO201637.0307003
In order to study the thermal effect of Yb∶YAG crystal endpumped by pulse laser diode(LD),the temperature distribution of crystal was calculated based on semianalytic method. The crystal thermal model was built under the real work situation and the initial conditions and boundary conditions were established in this research, according to the working characteristic of square Yb∶YAG micro crystal endpumped continuously by LD. Furthermore, considering the function relation between the coefficient of thermal conductivity and temperature and solving the heat conduction equation with Newton method, the temperature distribution was obtained. Finally, the influences of different factors such as the different pump power, super Gauss order, radius of spot, thickness of crystal on crystal were studied. The research results show that maximum temperature of Yb∶YAG crystal endpumped surface is 41.25 ℃ and 52.14 ℃,respectively, under the different conditions that thermalconductivity is constant and nonconstant. And in that case, the first order superGaussian light was used,with the output power of 80 W and the spot radius of 400 m, to pump the crystal with the mass fraction of 8% and the size of 431 mm3. It is very significant to reduce the thermal effect of full solid state Yb∶YAG crystal in this research.