2020 Vol. 41, No. 4

2020, 41(4): 1-6.
Study on parameters measurement technology of high energy and high power laser
LI Gaoping, CHEN Chao, LI Dong, WU Lei, ZHANG Biao, YU Dongyu, YIN Wanhong
2020, 41(4): 645-650. doi: 10.5768/JAO202041.0409001
The current situation and measurement requirements of high energy and high power laser technology were briefly described. The progress of parameters measurement research for high energy and high power laser in recent years was introduced, and the measurement principle and method of laser power energy, time-domain parameter and space-domain was given. The main problems of high energy and high power laser parameter measurement and the key technologies to be broken through are pointed out, including large dynamic range power energy “distortion-free” attenuation technology, laser power energy field measurement technology, power energy meter traceability and backscatter compensation method, etc.
Progress of terahertz metrology research and standard construction
DENG Yuqiang
2020, 41(4): 651-661. doi: 10.5768/JAO202041.0409002
Terahertz, as a novel technology, has been widely used in the field of material component recognition, high-speed communication, biomedicine, security imaging and military defense. Various applications of terahertz technology are based on the measurement of terahertz itself and its interaction with substances, therefore the accurate terahertz parameter measurement and relevant magnitude tracing are the technical support and guarantee of terahertz application. The measurement technology and tracing method, developed measuring instruments and devices, and established metrology calibration regulations, and metrology standard device formed in the terahertz radiation parameters metrology standard research by National Institute of Metrology were introduced. The magnitude tracing transitive graphs of terahertz radiation time domain, frequency domain, space domain and intensity were presented, and the measurement uncertainty analysis was carried out. The proposed terahertz metrology method and standard devices can guarantee the reliable magnitude in terahertz technology research and application, and can also provide a reference for other terahertz parameters measurement.
Research progress of particle field digital holography based on deep learning
WU Yufeng, WU Jiachen, HAO Ran, JIN Shangzhong, CAO Liangcai
2020, 41(4): 662-674. doi: 10.5768/JAO202041.0409003
In the digital holography of particle field, reconstructing a high-precision three-dimensional particle field distribution from a particle field hologram is one of the classic problems in the field of digital holography. Compared with the traditional inverse reconstruction algorithm, the deep learning algorithm can directly reconstruct the three-dimensional particle field from a single hologram to simplify the algorithm complexity and improve the calculation efficiency and accuracy rate. The research progress of particle field digital holography in combining deep learning algorithm with digital holography technology by the research teams at home and abroad was introduced. Starting from different methods of particle characterization, the application principles, implementation approach and accuracy rate of the support vector machine, fully connected neural network, fully convolutional network, U-Net network and deep neural network in the process of particle characterization and particle field inverse reconstruction for particle field holography were described. Finally, the advantages and shortcomings of deep learning algorithm in this research field were pointed out, and how to further improve the accuracy of this method was prospected.
High energy laser far-field irradiance distribution measurement technology and its developments
CHEN Chao, LI Gaoping, ZHANG Biao, WU Lei, YU Dongyu, YIN Wanhong
2020, 41(4): 675-680. doi: 10.5768/JAO202041.0409004
Measuring the high energy laser far-field irradiance distribution is an effective way to evaluate the performance of laser weapon system. Several existing measurement methods of high energy laser far-field irradiance distribution at home and abroad were compared and summarized. The advantages and disadvantages of various technologies were analyzed in detail, and the research progress of three key technologies, namely target surface anti-damage technology, sampling attenuation technology and power density calibration technology was introduced. On this basis, the development trend of direct measurement technology for high energy laser far-field irradiance distribution was described.
Three-dimensional deformation measurement based on digital speckle pattern interferometry
WANG Yonghong, BAO Fengqing, ZHANG Xiao, ZHAO Qihan, CHEN Weijie, YAN Peizheng
2020, 41(4): 681-689. doi: 10.5768/JAO202041.0409005
Three-dimensional deformation can be converted into stress-strain distribution, which is the key parameter in material performance test and structure reliability analysis. Among many three-dimensional deformation measurement techniques, digital speckle pattern interferometry can measure the three-dimensional deformation information with high precision. And it plays a very important role in the industries of aerospace, automotive, advanced equipment manufacturing, civil engineering, biomedicine and so on. Based on the basic principle of speckle pattern interferometry, several kinds of three-dimensional deformation speckle pattern interferometry were introduced in detail and their advantages as well as disadvantages were analyzed and compared; at the same time, the research progress and latest application of three-dimensional deformation speckle pattern interferometry at home and abroad were introduced; at last, the development trend of three-dimensional deformation speckle pattern interferometry in dynamic synchronous measurement, measurement system simplification and application range broadening was prospected.
Research on time domain parameters measurement of single pulse femtosecond laser
WU Lei, ZHANG Biao, YU Bing, YUAN Liang, CHEN Chao, XUE Yuanyuan, DONG Zaitian, YANG Hongru, LI Gaoping
2020, 41(4): 690-696. doi: 10.5768/JAO202041.0407001
The Ti sapphire femtosecond laser amplification system has the characteristics of low repetition frequency and complex pulse waveform. In order to accurately measure the peak power of the femtosecond laser amplification system, the measurement demand of single pulse waveform and pulse width was proposed. The measurement principle and method of single pulse femtosecond laser time domain waveform and pulse width were introduced, the time domain parameters measuring device of single pulse femtosecond laser based on frequency-resolved optical gating method was designed, and the technical problems and solutions in the calibration of time domain parameters measurement of single pulse femtosecond laser were discussed.
Vegetation canopy height inversion method based on spaceborne laser altimetry system
ZHANG Ying, LI Song, ZHANG Wenhao, LUO Min
2020, 41(4): 697-703. doi: 10.5768/JAO202041.0407002
When applied to the canopy height inversion, the spaceborne laser altimetry system cannot accurately extract the ground position from the echo signal due to factors such as large spot size and complex surface. Aiming at this problem, a new ground return position extraction and vegetation canopy height inversion algorithm was designed to classify the ground waveform and calculate the weighted elevation of effective candidate peak. The geoscience laser altimeter system (GLAS) echo data in the northwestern region of Vermont was processed by this method,so as to realize the ground elevation extraction and canopy height inversion. And the processing results were verified by the Lidar measurement data during the same period, as well as compared with the inversion results of Gaussian decomposition method. The results show that the ground return position extracted by the proposed method is very close to the distribution of ground point cloud collected by the airborne Lidar, and the ground extraction accuracy is better than that of the Gaussian decomposition method. The root-mean-square error (RMSE)and correlation coefficient of GLAS canopy height inversion result are respectively 2.82 m and 0.81, which are in good consistency with those of the airborne laser Lidar and superior to those of the Gaussian decomposition.
Research on measurement method of laser beam quality with orthogonal slit scanning
ZHAO Juncheng, YIN Wanhong, LIU Jianping, YANG Pengli, DONG Zaitian
2020, 41(4): 704-710. doi: 10.5768/JAO202041.0407003
In the traditional laser beam quality measurement method, an adjustable attenuation module is installed on the laser beam path in front of the change coupled device (CCD) camera target to attenuate the laser beam. However, the high-accuracy measurement is difficult to carry out due to the limitation of CCD camera pixel size by this method. On this basis, an evaluation method of laser beam quality with roller slit was proposed. In the measurement, the scanning slit on the slit roller was used to directly scan the measured laser beam, and the InGaAs detector was used to cooperate with the focusing lens for measurement. The high-accuracy incremental encoder was coaxial with the motor, which ensured the synchronous acquisition of position and data. According to the measured laser pulse frequency and the diameter range of the spot, the scanning frequency could be adjusted, and the resolution of spot spatial sampling was better than 1μm. The experimental results show that the value of laser M2 factor measured by this method is consistent with that provided by the measured laser, and the measurement uncertainty is less than 10%.
Study on calibration system and method of femtojoule laser energy meter
QIN Yan, HAN Zhansuo, LIN Lihong, WANG Jiangang, LI Jie, WANG Bing, YANG Hongru
2020, 41(4): 711-716. doi: 10.5768/JAO202041.0407004
In order to solve the calibration problem of the femtojoule laser energy meter, a special calibration system and method were proposed. The combination of fixed and variable two-stage attenuation mechanism was adopted in this system, which realized the calibration of laser energy meter with response wavelength of 1 064 nm, pulse width of 5 ns~1 μs and energy of femtojoule. The working principle, equipment composition and method of the calibration system were described. The key components and engine performance of the system were also described, and the corresponding test results were given: the uncertainty of energy repeat measurement was 3%, and the measurement uncertainty of the system could reach to 11%. Finally, the future improvement direction of the calibration system was proposed.
Optical properties measuring device based on tunable femtosecond laser
WANG Weimin, HE Yingwei, XU Yinuo, XU Nan, JING Xufeng, LIU Xiangliang, FU Yangting, GAN Haiyong
2020, 41(4): 717-722. doi: 10.5768/JAO202041.0407005
With the rapid development of laser technology, laser sources have been widely applied in the measurement of spectral radiation and optical properties. Compared with the traditional light sources, laser sources have the advantages of high power, wide spectrum and extremely low wavelength uncertainty. A set of photodetector response calibration device based on the wide-band tunable laser light source was established, in which the spectral coverage of the laser light source was 190 nm~4 000 nm, the laser pulse width was about 130 fs, and the repetition frequency was about 80 MHz. In order to avoid the impact of high peak power pulsed light on the calibration of the detector, and improve the linearity of the measurement, a converter of converting pulsed light to continuous light was successfully developed by using the inherent characteristics of the optical fiber. At the same time, a set of laser collimation and beam expansion optical paths was built based on the laser source, and a monochromatic uniform radiation field with an inhomogeneity of 0.29% was obtained at a wavelength of λ=550 nm. The monochromatic uniform radiation field plays an important role in the application of high-precision detector calibration, and the calibration measuring device based on it has a positive significance in the field of metrology.
Spectral calibration of atmosphere hyper-spectral resolution infrared sounder
KE Junyu, WANG Dongjie, GUO Yongxiang, ZHANG Mengyu, LIU Junhang
2020, 41(4): 723-729. doi: 10.5768/JAO202041.0406001
In order to calibrate the full spectrum band and high precision of the atmosphere hyper-spectral resolution infrared sounder, by analyzing the working principle of the interference spectrometer and theoretically deducing the spectral drift factor, it was found that the full spectrum band calibration could be realized by the limited spectral position correction. Based on the wavemeter, the method of spectral calibration with continuously tunable laser as the test light source was adopted, and the cross calibration with high-precision gas cell system was used to verify the calibration accuracy. The experimental results show that the test precision of the spectral calibration by measuring the spectral drift factor is better than 0.004 cm−1, which meets the calibration requirements of the high-precision spectrometer. The drift factor can be applied to the spectral calibration of the interference spectrometer.
Research on low-temperature infrared radiation measurement technology under vacuum condition
QIU Chao, ZHAI Siting, WU Kexuan, SUN Hongsheng, WANG Jiapeng, ZHANG Yuguo, YANG Wanglin, DU Jidong, GUO Yapin
2020, 41(4): 730-736. doi: 10.5768/JAO202041.0406002
According to the requirement of infrared radiation detection of low-temperature targets during the period of infrared payload serving in orbit, a low-temperature infrared radiation measurement scheme under vacuum condition was proposed, and the measuring device was developed. The measuring device was mainly composed of a low-temperature infrared optical system, a low-temperature mechanical structure, a low-temperature infrared detection system and a weak signal processing system. The low-temperature infrared radiation was gathered to the detector image plane through the optical system, the lock-in amplifier used coherent detection technology to extract the target signal, and the low-temperature infrared radiation was measured. After the development of the measuring device completed, the standard black body radiation source was used in the vacuum chamber to perform a low-temperature infrared radiation calibration test in the temperature range of 198 K to 423 K, which obtained the effective test data and the measurement uncertainty was within 5%. The proposed low-temperature infrared radiation measurement technology under vacuum condition can provide important data support for the design of low-temperature infrared target detection of infrared payload in orbital space.
Research of temperature uniformity and size-of-source effect in infrared spectral radiance measurement
HE Shufang, WANG Yanfei, DAI Caihong, LIU Jinyuan, FENG Guojin
2020, 41(4): 737-742. doi: 10.5768/JAO202041.0406003
Based on the existing national primary spectral radiance measurement facilities in the ultraviolet, visible and near-infrared wave bands, the measurement range of spectral radiance was extended to 2 µm~14 µm infrared band, which could be used for the metering calibration device of infrared spectral radiance and provided technical support for infrared spectral radiometric calibration in the fields of remote sensing earth observation, climate change, target recognition, material emissivity measurement and so on. The temperature uniformity and size-of-source effect of infrared spectral radiance measurement were studied. The temperature uniformity was improved by customizing the apertures or limiting the cavity position to be used in the system; the analysis and suppression of size-of-source effect were carried out by using optical simulation method, adopting limiting apertures in the system, simplifying the optical path and so on, which effectively decreased the uncertainty of the size-of-source effect. Next, the nonlinear effect and other parameters of the system will be studied, and the total uncertainty will be evaluated.
Design and performance test of self-calibration multichannel infrared radiometer
ZHANG Yunxiang, LI Xin, LI Chen, ZHENG Xiaobing
2020, 41(4): 743-753. doi: 10.5768/JAO202041.0406004
In order to meet the needs of automated observation calibration for remote sensor thermal infrared band, a self-calibration multichannel infrared radiometer with automated observation capability was developed. The equipment has the following features: 1) the design of motor-driven gold-plated reflector was used to achieve the measurement of downward atmospheric radiation and surface radiance at an elevation angle of 0°~90°, which provided the technical means to eliminate the influence of downward atmospheric radiation on inversion surface temperature; 2) the filter wheel spectrometry was used to realize the automatic setting of 6 spectral channels, and combined with the multichannel temperature and emissivity separation algorithm, the separation of site temperature and emissivity could be achieved, which provided 2 key factors for the absolute radiometric calibration of satellite remote sensor thermal infrared band; 3) a black body with two built-in temperature control accuracy better than 0.04 K and 0.05 K, emissivity higher than 0.994, stability better than 0.001 4 was used to achieve the real-time radiometric calibration of the internal detector, which effectively eliminated the influence of internal background radiation on radiation measurement. The calibration uncertainty is less than 0.167%, and the equivalent temperature measurement uncertainty is 0.2 K (@303 K, 11 μm), which lays the foundation for the application of site automated calibration for remote sensor thermal infrared band.
Missile-borne measuring device of effective light intensity spatial distribution for pulsed light source
YUAN Liang, QIU Lirong, KANG Dengkui, LI Hongguang, LIU Ruixing, LU Fei, YU Bing, JIANG Changlu, WANG Shengyun
2020, 41(4): 754-760. doi: 10.5768/JAO202041.0410001
The Blondel-Rey method of effective light intensity spatial distribution for pulsed light source was studied. The measurement of instantaneous light intensity was realized by adopting the composite trapezium numerical integration, and the spectral mismatch correction of high color temperature light source measurement was analyzed. Based on the principle of double-reflector synchronous measurement, a measuring device of effective light intensity spatial distribution for pulsed light source was established. The key components such as whole space distributed rotating platform, pulsed light intensity detection system and high resolution spectrometer for spectral mismatch correction were analyzed in detail. And the measuring device was calibrated by using the high color temperature modulation light source. Finally, the measurement uncertainty of this measuring device was analyzed, and the expanded uncertainty could reach to 3.0%.
Nitrate nitrogen concentration detection method based on principal component analysis and BP neural network
CHEN Peng, YAN Xianze, HAN Yangyang, WU Chenyang, ZAN Hao
2020, 41(4): 761-768. doi: 10.5768/JAO202041.0410002
Aiming at the problem of inaccurate detection of the nitrate nitrogen solution concentration with interfering substances in ultraviolet spectrophotometry (UV method), a nitrate nitrogen concentration detection method based on principal component analysis (PCA) and BP neural network was proposed. First, the absorbance of the nitrate nitrogen reagent at 196 nm~631 nm was measured by the material composition detection system of the micro-spectrometer, which was divided into test set and training set. Then, the PCA was used to calculate the training set to obtain the principal components. Finally, a three-layer artificial neural network was built based on the BP algorithm. The obtained principal components were divided by 8 and input into the network for training. During the training, the leaving-one method was adopted for cross-validation. This model was used to calculate the training set and test set, the mean relative error between the obtained results and the true concentration is 2.411 5% and 1.553% respectively. The experimental results show that the method can better detect the concentration of the nitrate nitrogen reagent with interfering substances.
Research on image shooting technology in strong firelight
YAO Delong, CHEN Song, WEI Zhuo
2020, 41(4): 769-772. doi: 10.5768/JAO202041.0410003
The near ultraviolet band spectrum analysis was carried out on the firelight to the first stage warhead of series warhead, 310 nm~320 nm was selected as the shooting window of the high-speed camera, and the narrow band filter was used to filter out other spectra besides the shooting window. The objects in the firelight were illuminated at 320 nm with the auxiliary of laser, and the images of the objects in the strong firelight were clearly captured. Furthermore, the scientificity and effectiveness of the system were verified through the target penetration test of the series warhead.
Research on resolution calibration device and method of ultraviolet image intensifier
WANG Shengyun, SHI Jifang, XIE Qi, SUN Yunan, YU Bing, LI Hongguang, KANG Dengkui
2020, 41(4): 773-777. doi: 10.5768/JAO202041.0409901
The UV (ultraviolet) image intensifier is the core part of the missile UV warning system, UV early warning system and the various UV radiation monitoring systems, and the accuracy of its parameters directly affects the image quality of the system. In order to ensure the accuracy of the test data, an resolution calibration device of the UV image intensifier was developed. The UV light source used in the resolution calibration device of the UV image intensifier was the UV light with a wavelength range of 200 nm to 400 nm. The corresponding resolution targets, filters, and the optical imaging systems were all required the ability to transmit the UV light. Due to the short wavelength of the UV light, it was easy to generate a great deal of stray light caused by the scattering effect. The UV quartz was adopted by the designed resolution target, the transmission structure was adopted by the UV optical imaging system, and the coaxial conjugate lens was selected as the UV optical imaging system. The experiment and the measurement uncertainty analysis verify that the measurement uncertainty of the calibration device is 5%.
Research for calibration technology of ultraviolet-vacuum ultraviolet imaging spectrometer
SUN Hongsheng, SUN Guangwei, WANG Jiapeng, ZHANG Yuguo, LI Shiwei, ZHAI Siting
2020, 41(4): 778-785. doi: 10.5768/JAO202041.0409902
UV-VUV imaging spectrometer has been widely used in space exploration in China. It needs to be calibrated in its development process. However, there is no corresponding measurement standard in China, which can not guarantee the accuracy and reliability of the measurement results. Therefore, a calibration device and method of UV-VUV imaging spectrometer was designed to calibrate the parameters of UV-VUV imaging spectrometer, such as spectral range, wavelength, spectral responsivity, spatial angular resolution, uniformity, etc. The results show that the uncertainty of wavelength measurement is 0.08 nm ( k=2), the uncertainty of spectral responsivity measurement is 6.8% ( k=2), the uncertainty of spatial angular resolution measurement is 0.022 mrad ( k=2), and the uncertainty of uniformity measurement is 4.2% ( k=2).
Application of terahertz spectroscopy in THDCPD isomers detection
WU Bin, YANG Yanzhao, YING Chengping, LIU Hongyuan, ZHANG Peng, WANG Hengfei
2020, 41(4): 786-790. doi: 10.5768/JAO202041.0409903
The application of terahertz spectroscopy in the identification of energetic material isomers was studied. Firstly, a terahertz time-domain spectrometer for specific engineering application was developed, and its environmental adaptability was verified by vibratory impulse and temperature variation experiments, which indicated the spectrometer could work stably and reliably in a non-laboratory environment. Secondly, the validity of spectrum measurement for the spectrometer was verified by carbon monoxide standard gas, and the calibration of measuring frequency was realized at the same time. The terahertz spectrum of two isomers endo-THDCPD and exo-THDCPD of THDCPD were measured by the calibrated spectrometer. The results show that there are significant differences between terahertz spectrum of two isomers. The terahertz spectrum of endo-THDCPD presents the obvious characteristic absorption at 0.23 THz and 1.70 THz, while the 2 most obvious characteristic absorption peaks of exo-THDCPD are at 1.28 THz and 1.60 THz. Therefore, the use of terahertz spectroscopy can effectively distinguish the two kinds of isomers with only slight difference, which has reference significance for the application of terahertz spectroscopy in the research field of energetic material.
Single test error analysis for integral sensitivity of low-light-level image intensifier
BAI Xiaofeng, CHENG Hongchang, HE Kaiyuan, HAN Kun, YANG Shuning, LI Junguo, CHEN Xulang, DANG Xiaogang, WANG Lei
2020, 41(4): 791-795. doi: 10.5768/JAO202041.0404001
In order to improve the test speed of performance parameter for lot size of low-level-light (LLL) image intensifiers, the single test data is usually used as the measurement result. In this case, the error of parameter single test result will directly determine the accuracy of the performance evaluation result. The parameter test of integral sensitivity for LLL image intensifiers was taken as an example to evaluate the single test error. Based on the comprehensive analysis of the errors of test method, measuring device, data calculation and so on for the integral sensitivity of LLL image intensifiers, the single test maximum error of integral sensitivity was calculated to 6.7%. On this basis, the single test error control scheme of integral sensitivity using a diaphragm with higher processing accuracy, corrected incident illuminance measurement position, and stage auxiliary parameter repeatability measurement calibration was proposed. The research results have important guiding significance and reference value for the rapid test of lot size of LLL image intensifiers.
Research on afterglow measurement method of image intensifier based on P31 phosphor powder
YAO Ze, CHENG Hongchang, LI Tao, ZHOU Yujian, HUANG Wujun, LI Dan
2020, 41(4): 796-800. doi: 10.5768/JAO202041.0404002
The fluorescent screen afterglow of low-level-light(LLL) image intensifier plays a decisive role in the application of high frame rate photon counting system. According to the test method of fluorescent screen afterglow in the GJB 7351-2011 General Specification for Super Second Generation Image Intensifier , the light pulse was used as the excitation source. In this method, the illuminance of the light source dropped slowly when the light pulse excitation source stopped, which resulted in inaccurate test results in the measurement of afterglow time of short afterglow powder (μm level) and medium afterglow powder (ms level). Aiming at this problem, under the condition of continuous illumination, a test method of fluorescent screen afterglow with the voltage pulse signal of photocathode as the excitation source was proposed. In this method, the characteristics of the photocathode ultra fast response time (generally about 1 ns) and the shorter edge time (generally it can be controlled within 10 ns) of the voltage pulse signal improved the influence of excitation source time response on the accuracy of fluorescent screen afterglow test results. Based on this method, a set of fluorescent screen afterglow measuring device of LLL image intensifier was set up, and the repeatability measurement of domestic three generations LLL image intensifier afterglow of P31 phosphor powder was carried out. The error analysis of measurement uncertainty is carried out, and the expanded uncertainty is 3.2%, which reaches the accuracy requirements of traditional photpelectronic testing instrument, and can meet the requirements of afterglow measurement of LLL image intensifier fluorescent screen. The research results provide a detection method for higher performance products.
Distortion correction research by gravity for 300-mm-aperture flat based on multi-point adjustable support
WANG Yuntao, CHEN Lei, CHEN Jia, ZHANG Zhengyu, KONG Lu
2020, 41(4): 801-809. doi: 10.5768/JAO202041.0409801
In the field of high-precision optical elements, especially the planar optical elements with large aperture, the deformation by gravity becomes an inevitable problem with the improvement of requirements for higher measuring accuracy and larger aperture. The system design of vertical Fizeau interferometer and the deformation theory of multi-point adjustable support method were introduced.By finite element method (FEM) analysis, the reasonable support structure is optimized and derived. Calibration of deformation of flat by gravity was obtained on 300-mm-diameter vertical Fizeau interferometer with liquid surface datum. Comparing it with detection result by three-flat method, the residual between two methods can reach 10.20 nm for peak valley (PV), and 1.56 nm for root mean square (RMS).
Measurement method research for Micro-CT system based on combined calibrator
SHA Tongtong, HU Xiaodong, ZHAO Jintao, ZOU Jing
2020, 41(4): 810-815. doi: 10.5768/JAO202041.0409802
In order to ensure the measurement accuracy of the Micro-Computed Tomography (Micro-CT) system, a combined measurement mode of the calibrator and the sample was adapted to design the combined calibrator which can be used for the combined measurement, and a method to correct the proportional error and the threshold error in the measurement process of the Micro-CT system was proposed. Without changing the scanning parameters of the Micro-CT system, the samples of polytetrafluoroethylene, a light material commonly used in aerospace, were measured independently and compared with the measurements based on the combined calibrator. The results show that compared with the sample independent measurement method, the proposed method can effectively reduce the measurement error of 1 μm~4 μm and has better robustness.
Large angle range beam scanning control based on crystal spatial light modulator
ZHENG Xinbo, ZHANG Xuan, LUAN Lin, HONG Hanyu
2020, 41(4): 816-821. doi: 10.5768/JAO202041.0409803
In order to realize the laser scanning control within 90° cone angle, a beam deflection and angle amplification optical path system based on LCSLM (liquid crystal spatial light modulator) were researched and established by using the advantages of high precision and no mechanical inertia in beam deflection control. The programmable phase modulation algorithm and angle amplification optical path structure of spatial light modulator was proposed. The relations between the beam deflection angle of spatial light modulator and the phase gray scale driving diagram was derived, and the angle amplification optical path system with an angle magnification ratio higher than 22 times was designed. On this basis, the experimental system of beam scanning control was established, the angle emergence range of the device was measured, and the actual angle magnification ratio was compared with the designed value. The experimental results show that the emergence field angle of the developed system can reach to 91.22°, and the regular shape scanning within the range of emergence field angle by distortion correction can be realized. This research has important research value and application prospect in the fields of beam agile control, wireless laser communication, target search and tracking.
Calibration method of light field refocusing position in 3D dose measurement system based on scintillator
YAN Xuewen, HE Liang, LI Hua, LI Deyuan, ZHANG Xiaodong
2020, 41(4): 822-828. doi: 10.5768/JAO202041.0409804
3D dose distribution measurement in radiotherapy based on scintillator light field imaging was achieved by 3D reconstruction of scintillation light produced by the scintillator energy deposition. The refocusing position of the image obtained by the light field camera affected the accuracy of the scintillation light 3D reconstruction. A method of refocusing position calibration using checkerboard calibration plate was presented. The checkerboard calibration plate in a known position was captured by the Lytro Illum light field camera, and the focus stack sequence was obtained by the light field data processing. The Gaussian defocusing parameter σ of all refocusing images was obtained by the knife-edge method, and the refocusing parameter α corresponding to the minimum σ is obtained. Finally, the corresponding relationship between some α and refocusing position was given to complete the refocusing position calibration. Compared with the commonly used scale calibration method, the Gaussian defocusing parameter can be reduced by 2 % to 10 %, which is helpful to improve the measuring accuracy of the 3D dose in radiotherapy.
Integrated design of three-dimensional continuous displacement measurement with temporal speckle interferometry
LIU Zihui, GAO Zhan, GAO Chenjia, WANG Xu, ZHONG Chuqian, LIU Yuchen, ZHANG Yuan
2020, 41(4): 829-836. doi: 10.5768/JAO202041.0409805
The three-dimensional electronic speckle pattern interferometry (3D ESPI) is widely used in many fields due to its ascendancy of non-contact, high precision, high sensitivity and full-field measurement. In order to realize the non-contact dynamic full-field 3D measurement, a compact and complete 3D measurement system was designed and set up. Three independent lasers were replaced by a single multi-wavelength fibre coupling laser to produce the speckle pattern interferograms of out-of-plane and in-plane, which could be captured and processed by only one charge coupled device (CCD) camera. The entire measurement system adopted cage construction with high flexibility and stability. The phase unwrapping algorithm based on the wavelet transform was programmed to realize the complete extraction of 3D displacement information on the measured object. The experimental results show that this measurement system can obtain the 3D displacement of the measured object. The 3D displacement values in the experiments are 17.68 μm, 36.23 μm and 13.85 μm, compared with the actual displacement values of 18.1 μm, 36.4 μm and 14.0 μm, the absolute errors are 0.42 μm, 0.17 μm and 0.15 μm, respectively,and the relative errors are 2.3%, 0.5% and 1.1%.
Multi-level detection method for PCB board defects based on improved template matching and image difference
ZHU Han, LIN Li, WANG Jianhua, CHEN Jian
2020, 41(4): 837-843. doi: 10.5768/JAO202041.0409806
Aiming at the insufficient accuracy of the template matching methods and the defect detection methods used in PCB defect detection system, a multi-level detection method for PCB board defect based on improved template matching and image difference was proposed. Firstly, an improved template matching method based on multi-direction Sobel operator was proposed to realize the matching between the tested image and the template image. On this basis, a multi-level binaryzation detection method based on image difference was proposed to realize the defect detection of PCB image. Combined with the results on the experimental platform, the proposed method can extract the defect area accurately. The false detection rate of this method is only 5%, which has better stability and higher accuracy.
Method of optical flat elements surface figure detection with high accuracy based on phase measurement deflectormetry
LI Dahai, WANG Ruiyang, ZHANG Xinwei
2020, 41(4): 844-856. doi: 10.5768/JAO202041.0405001
Aiming at the phase measurement deflectormetry(PMD), it is difficult to control the low-order error of surface figure in optical elements surface figure detection with high accuracy. The basic principle of the optical flat elements surface figure detection by PMD was introduced. The research progress of improved surface figure reconstruction algorithm and systematic error deduction method of relative detection and four-step shearing of PMD technology was described. Based on PMD technology, the splicing detection of flat glass with the size of 398.7 mm×422.8 mm and the elimination method of parasitic reflection influence existed in the flat elements were analyzed. The RMS of detection accuracy of established 6-camera slope splicing detection system could reach to 1 µm. Multi-frequency fringe method and binary fringe method could be effectively eliminated the influence of parasitic reflection, which provided a feasible scheme for the surface figure detection with high accuracy of front and rear surfaces of the large-caliber optical flat elements.
Geometric characteristics and error analysis of standard spherical lens
YUAN Qun, JI Wen, GAO Zhishan
2020, 41(4): 858-868. doi: 10.5768/JAO202041.0405002
The standard spherical lens plays an important role in the Fizeau interferometer. The geometric characteristics and error analysis of standard spherical lens were reviewed. The effect of standard spherical lens on interference illumination optical path and imaging optical path was first analyzed; the R-sinθ geometric characteristics relation model of spherical interference imaging was emphatically introduced and verified with experiments; a new design method of aspheric surface splitting using Q aspheric surface was described, and an two-piece type aspheric standard spherical lens structure was presented; the research results of spherical adjustment error to be measured and phase shift space nonuniformity error for small F-number standard spherical lens were summarized; a wave surface difference algorithm for correcting errors in a spherical interferometer was presented; the effect of retrace error when measuring the spherical surface at the focal position near the standard spherical lens was pointed out; from the conjugation relation angle of object image, the reason of large retrace error of near focal position was explained, and the effect of transmission wave front and slope of standard spherical lens on retrace error was analyzed. The geometric characteristics relation which should be paid attention to when designing the standard spherical lens, the errors which were easy to generate when using the standard spherical lens and the corresponding suppression methods were put forward.
Study on automatic measurement method of elastic modulus for optical glass
GUO Changli, HUANG Zhang
2020, 41(4): 869-875. doi: 10.5768/JAO202041.0405003
In order to solve the problems of long measuring period and complex measurement process of elastic modulus for optical glass, a method of quickly measuring the elastic modulus of small sample optical flat glass by computer image processing technology was proposed. Firstly, based on contact mechanics theory and Newton ring interference principle, the analytical formula for measuring the elastic modulus of optical glass was deduced. Secondly, taking advantage of the image processing technology, the Newton ring interference image was taken by camera, and the interface program of MFC monitoring and single image shooting was designed to automatically measure the center black spot radius of Newton ring interference image. Finally, according to the relationship between the elastic modulus of optical glass, the center black spot radius of Newton ring interference image, and the center stress of Newton ring, the fast measurement of the elastic modulus of small sample optical glass was realized. The experimental results show that the relative error of the elastic modulus for optical glass is no more than ± 8.8% in the range of stress 31.17 N~55.11 N, and ± 16% in the range of stress 55.11 N~71.07 N.
Structural texture defects detection method based on frequency domain texture elimination
WU Hao, XU Xiangrong, XU Sixiang
2020, 41(4): 876-880. doi: 10.5768/JAO202041.0405004
The existence of structural texture can interfere with the defects (such as scratches) detection for the surface texture images defects detection of machined surface. The method of eliminating background texture in frequency domain was studied for the defects detection. Firstly, based on the image restoration technology of Fourier transform, the structural texture in spatial domain image corresponded to the high energy frequency component in Fourier domain, which was removed by the least square method linear fitting, and these energies were set to zero finally transformed into the spatial domain image. In the restored image, the structural texture region in original image became an approximate uniform gray level, in which the defective region was preserved. And then the statistical process control was used to set threshold to separate the defects from the restored image. Finally, experiments on a series of structural texture images show that the proposed method is feasible and effective.