2022 Vol. 51, No. 9

Lasers & Laser optics
Photoelectric measurement
Research on rotating splicing of point cloud in workpiece wall based on surface structured light
Liu Jinyue, Zhai Zhiguo, Jia Xiaohui, Xue Luming, Li Tiejun
2022, 51(9): 20210952. doi: 10.3788/IRLA20210952
[Abstract](103) [FullText HTML] (21) [PDF 1564KB](39)
In order to solve the problem of limited internal space and difficult measurement of some workpiece, a point cloud rotating splicing method based on surface structured light was proposed. The reconstruction method of single field of surface structured light was introduced in this paper. The absolute phase value was obtained by combining four-step phase shift and complementary Gray code, and the camera and projector were calibrated by polynomial fitting method. The point cloud registration was studied based on the rotation plane of the wrist joint at the end of the manipulator. A calibration method based on the auxiliary camera was proposed, and the transformation relationship between the camera imaging coordinate system and the rotation plane coordinate system was given. The experimental results show that the method is suitable for measuring the inner wall of workpiece, and the average error of splicing is less than 0.05 mm, which meets the requirements of practical application.
Research on optical scattering characteristics of targets based on single photon detection
Li Zhiting, Liu Changming, Wang Yuye, Chang Jiying, Chen Kai, Li Jining, Zhong Kai, Xu Degang, Yao Jianquan
2022, 51(9): 20210825. doi: 10.3788/IRLA20210825
[Abstract](135) [FullText HTML] (26) [PDF 1764KB](64)
The single photon scattering echo characteristics of targets were studied in this paper. An optical scattering characteristic measurement system was built based on infrared single photon detector and picosecond laser. The number of echo photons was used to characterize the optical scattering characteristics under the condition of single photon detection. In this experiment, the single photon scattering characteristics of targets with different shapes (sphere, cube, cylinder and cone) were studied. And the results were fitted by using the bidirectional reflection distribution function model. The experimental results were in good agreement with the theoretical fitting ones. Further, the single photon scattering characteristics of targets with different materials (ceramic tile, wood and wall brick) were studied, which were compared with the traditional wave scattering characteristics. This study provides a reference for the long-range target recognition and detection of single photon lidar.
Calibration method of quad-camera measurement system based on tensor decompose
Li Yunhui, An Dongyang, Miao Zhonghua
2022, 51(9): 20220103. doi: 10.3788/IRLA20220103
[Abstract](90) [FullText HTML] (37) [PDF 2969KB](48)
Camera calibration is essential for vision measurement. In order to realize the accurate calibration of the multi-camera measurement system, the existing multi-camera calibration methods based on 1D (one-dimensional) targets are analyzed, and a multi-camera calibration method based on tensor decomposition is proposed. The method includes three aspects: (1) A mathematical model of multi-camera calibration is established with pin-hole model and rigid body transformation theory; (2) A problem of multi-camera calibration approach based on the fundamental matrix is analyzed, which is the calibration results coupled with each other; (3) In order to address this problem, the quad-focal tensor of a quad-camera measurement system is introduced to the calibration process, which includes that the quad-tensor is solved by using the image point of 1D calibration objects, and a reduced method for the quad-focal tensor is used to refine the camera matrices. Finally, the effectiveness and accuracy of the method are verified by experiments. The results indicate that (1) The calibration of the quad-camera 3D measurement system can be realized by only 3 groups of calibration target images, and the calibration operation efficiency is higher than that of the basic matrix method, and (2) the accuracy of the multi-camera measurement system reaches 4 mm (3σ) in the range of 4000 mm×4000 mm×2000 mm, which is more accurate than traditional approaches with only 3 groups calibration images. The proposed method meets the requirements of accurate measurement of indoor moving target pose.
Design of laser parameter measurement system based on diffuse reflection imaging
Cheng Yilun, Tan Fengfu, He Feng, Hou Zaihong, Qin Laian, Wang Hao, Huang Zhigang, Wu Decheng
2022, 51(9): 20210921. doi: 10.3788/IRLA20210921
[Abstract](98) [FullText HTML] (20) [PDF 1415KB](43)
Accurate measurement of laser spot parameters after transmission in the atmosphere is a key technical means for studying the effects of laser atmospheric propagation and analyzing the performance of laser emission systems. The methods of measuring laser far-field parameters mainly include array detection method and camera imaging method. However, the current measurement and analysis of laser atmospheric transmission effect basically use array detection method. Because the detector array target detectors cannot be arranged uniformly and tightly due to the limitations of space physics and R&D costs, this will cause the distortion of the sampling spot and the far-field spot parameters cannot be accurately measured. Aiming at this problem, a set of laser parameter measurement system based on diffuse reflection imaging method is designed in combination with the high resolution of the camera. The minimum measurement resolution of the system is less than 0.39 mm, and the average deviation of the centroid position is 0.05mm, the uncertainty of the power from the measurement spot to the target is better than 10%. The system can effectively measure the tracking accuracy and target power of the laser emission system, and has accumulated a certain theoretical basis and experimental data for analyzing the laser atmospheric transmission effect and analyzing the performance of the laser emission system.
Calibration method and accuracy evaluation of visual target with double screen for straight pipe jacking machine
Huang Zhe, Yan Qingde, Li Qian, Cheng Erjing, Shen Xiaoling, Xu Yeqian
2022, 51(9): 20210933. doi: 10.3788/IRLA20210933
[Abstract](129) [FullText HTML] (24) [PDF 1619KB](30)
Aiming at the problem that it was difficult to calibrate the position and attitude relationship between the front and rear photosensitive imaging screens of visual target with dual-screen, a method for calibrating the position and attitude of the photosensitive imaging screen based on points-cloud was proposed. The front and rear photosensitive imaging screens were respectively divided into grid arrays of n rows and n columns. Combining the image 2D coordinates which were obtained in real time by industrial cameras and the spatial 3D coordinates which were measured by a total station to obtain the 2D-3D mapping relationship of each grid corner point on the photosensitive imaging screen, the coordinate point cloud data were acquired. Next, the 3D coordinates of the coordinate point cloud data are converted to the target coordinate frame according to the three common point coordinate frame transformation algorithm, which can determine the positional relationship between the camera and front/rear photosensitive imaging screen. And then the positional relationship between the front and rear photosensitive imaging screens was solved by the grid indexing method. In order to evaluate the accuracy of target attitude measurement, the static repeatability and the absolute measurement accuracy evaluation experiments were designed. The experimental results show that the static repeatability accuracy of the coordinates is 0.13 mm, the absolute accuracy of the coordinates is 0.93 mm, the static repeatability accuracy of the heading angle is 0.01°, and the absolute accuracy of the heading angle is 0.05°. Therefore, the calibration method can realize the accurate calibration of the pose of two spatial planes, which has the characteristics of simple operation and high precision, and can be used for calibration of visual target with double screen.
Research on time-stretched photon Doppler velocimetry
Lv Linjie, Wu Tengfei, Han Jibo, Zhao Lijie, Ma Pengmou, Chen Xiangmiao
2022, 51(9): 20210809. doi: 10.3788/IRLA20210809
[Abstract](100) [FullText HTML] (27) [PDF 1650KB](39)
In the transient high-speed velocity measurement scene, the target accelerates to several-tens of km/s in tens of ns. Therefore, the Doppler frequency shift can reach GHz or even hundreds of GHz. The velocity measurement range of photon Doppler velocimetry was limited by the current electrical digital to analog conversion technology. The time-stretched photon Doppler velocimetry used the time-stretched characteristic of femtosecond laser to reduce the signal frequency in the optical domain, which reduced the pressure of photoelectric signal detector and electrical digital-to-analog conversion device. An improved time-stretched photon Doppler velocimetry system was proposed in this paper. The femtosecond pulse was fully widened and spread over the whole time domain through the first stage dispersion fiber, in order to avoid the sampling interruption of velocity signal; In signal demodulation, error compensation algorithm was used to compensate the frequency shift signal, which reduced the system error caused by displacement and increased the effective recording time. Nanosecond laser was used to drive the aluminum film to produce high-speed flyer in the experiment, and the experimental results of the paper speed system were tested in the recording time of 1.2 µs. The repetition frequency 50 MHz femtosecond laser was used in the experiment. The first and second stage dispersion devices used 200 km and 100 km single-mode fiber, forming a scale factor of 2/3. In the end, the experiment showed that the Doppler shift signal of 3.6 GHz was reduced to 2.4 GHz, which was compared with the photon Doppler velocimetry system, and the experimental error was less than 5%. The system will be able to apply velocity measurement under dynamic high pressure technology loading flyer scene, and provides new measures for transient high-speed measurement area.
Directivity calibration and correction of bracket for star sensor
Li Yuanpeng, Guo Jiang
2022, 51(9): 20210875. doi: 10.3788/IRLA20210875
[Abstract](114) [FullText HTML] (20) [PDF 1827KB](40)
In order to ensure the high-precision pointing of bracket for star sensor after installation, a technical method for quantitative grind of bracket for star sensor was proposed. Firstly, we established the star sensor bracket’s coordinate system by constructing the virtual horizontal axis, then obtained the angle relationship between any two coordinate axes by the theodolite interactive measurement and sequential solving strategy. According to the results, we got the posture transformation matrix between star sensor bracket’s actual coordinate system and the space camera’s coordinate system. By the technical requirements of the star sensor bracket’s installing, we acquired the posture transformation matrix between the ideal star sensor bracket’s coordinate system and the space camera’s coordinate system. Then, we obtained the posture transformation matrix from the actual coordinate system to the ideal coordinate system by bridge of the camera coordinate system. According to this result, the corrective value of bracket for star sensor was accurately solved. The experimental research shows that this method can improve the star sensor bracket’s pointing accuracy from the initial 760″ to less than 10″ after two rounds of iteration, which proves effectiveness of the method. At the same time, directivity calibration and correction of bracket for star sensor can also guide the precise assembly and adjustment of other two components with spatial free angle relationship.
Quantitative analysis research of ChemCam-LIBS spectral data of Curiosity rover
Zhang Pengfei, Zhou Ting, Xia Daohua, Zhang Li
2022, 51(9): 20210962. doi: 10.3788/IRLA20210962
[Abstract](210) [FullText HTML] (50) [PDF 3018KB](39)
The traditional partial least squares method and support vector machine regression method were often difficult to obtain high accuracy and further optimization in predicting the element content of the ground standard sample of the rover corresponding to the spectrum. To solve the above problems, the three-channel folding of high-dimensional spectral information was carried out to eliminate its matrix effect in the research, and introduced the Residual Network structure (ResNet), which was good in the field of computer vision, to extract the spectral features and predict the corresponding principal component content. In this paper, the full connection layer in ResNET network structure was removed to prevent the sudden increase of model parameters, and the last Softmax classification sublayer of the network was changed into a linear rectification layer for prediction. At the same time, exponential learning rate attenuation and Dropout mechanism were added to make the model prediction results have higher accuracy and generalization ability. Compared with linear support vector machine regression (LinearSVR) and depth separable convolution network Xception, the prediction root mean square error of each main element content of the model decreases by 30% and 17% on average, respectively. The experimental results show that the regression model established by ResNet network shows good prediction characteristics when LIBS technology is used for principal element quantitative analysis of ChemCam spectral data.
Measurement technique research for the absorptivity of cryogenic radiometer absorbing cavity at the 4 K temperature
Yu Bing, Fan Jihong, Yuan Linguang, Li Yan, Guo Lei, Wang Xiao, Chu Junwei, Qin Yan, Sun Yunan, Zhang Deng, You Yue, Jin Weiqi
2022, 51(9): 20210984. doi: 10.3788/IRLA20210984
[Abstract](125) [FullText HTML] (31) [PDF 1292KB](33)
In order to realize measuring the absorptivity of cryogenic radiometer absorbing cavity at the 4 K temperature, a method of measuring the absorptivity with variable temperature is researched. By designing reflection monitoring components in front of the Brewster window of the cryogenic radiometer, and controlling the cryogenic radiometer to work in a vacuum environment of 10−6 Pa, then adjusting the refrigeration temperature of the cryogenic radiometer, the reflection signals of the cryogenic radiometer absorbing cavity are measured at 632.8 nm under room temperature and different temperature conditions. Combined with the measurement results of the reflectance at 632.8 nm of the cryogenic radiometer absorbing cavity at room temperature using the traditional integrating sphere method, the absorptivity of the cryogenic radiometer absorption cavity can accurately obtain under different temperature conditions through calculations. The experimental measuring the absorptivity of the absorbing cavity at room temperature and 4 K temperature, the absorptivity is 0.99976 and 0.999 71, respectively. The measurement uncertainty of the absorptivity of the cryogenic radiometer absorption cavity at the 4 K condition is evaluated, and the results obtained show that the relative expanded uncertainty is 0.005%(k=2).
Holographic microscopy detection method of microfluidic chip channel
Xu Jianan, Kong Ming, Liu Wei, Wang Daodang, Xie Zhongsi
2022, 51(9): 20210915. doi: 10.3788/IRLA20210915
[Abstract](88) [FullText HTML] (22) [PDF 2218KB](33)
Aiming at the detection requirements of the microfluidic chip channel and defect detection, a set of reflective image-plane digital holographic microscopic system based on the pre-amplified off-axis optical path was designed and constructed. In the digital holographic microscopy measurement, the phase distortion correction method of the low-spatial frequency objects whose lateral size occupies a relatively large field of view was discussed, and the two-step phase subtraction method was proposed to be more suitable for the phase distortion correction of this type of object. The phase distortion correction effects of two-step phase subtraction method, general polynomials surface fitting method and Zernike high-order polynomials surface fitting method were compared and analyzed through the experiment of a micro-step standard sample with a width of 55 μm and a height of 65 nm. The analysis results show that the relative error of the average height of the micro-step after the distortion is corrected by the two-step phase subtraction method is 1.1%, which is smaller than other methods and has a better distortion correction effect. In addition, the microfluidic chip with a channel width of 80 μm was used as the sample to detect the three-dimensional shape of the micro-channel, the fracture defect and defective defect on the surface of the channel. The quantitative results show that the width of the fracture defect is 14.1 μm and the depth is 431.7 nm. The defective defect has a width of 33.6 μm and a depth of 295.1 nm. The experimental results show the image-plane digital holographic microscopic system provides a new way for the rapid and non-destructive measurement of microfluidic chip microchannels and surface defects, which is of great significance for the quality evaluation of microfluidic experimental systems.
Research on ground detection model and test of optical reconnaissance satellite
Xing Hui, Zhang Yanxiu, Lei Ping, Ma Na, Wang Juanfeng, Kang Dayong
2022, 51(9): 20210978. doi: 10.3788/IRLA20210978
[Abstract](151) [FullText HTML] (24) [PDF 1470KB](47)
In the field of space optoelectronic countermeasures, the real-time on-orbit tracking of satellites by ground optoelectronic tracking equipment is a prerequisite for interference countermeasures, and optical reconnaissance satellites mostly operate in sun-synchronous orbits. Firstly, according to the optical reconnaissance satellite earth observation was apparent under vertical or lateral swing down more visual, and ground jamming equipment must be located within the optical reconnaissance satellite view characteristic, through independent mathematical deduction, the mathematical model of satellite and ground equipment location relationship between each other, including the ground photoelectric devices of optical reconnaissance satellite observation distance and the mathematical expression of observation angle; Secondly, according to the radiation scattering characteristics of the satellite and their solar panel, as well as the scattering transmission characteristics of the earth's atmospheric environment and terrain background in the visual band, the mathematical model of the scattering radiation transmission of the star and the observation path was derived, and the mathematical expression of the illuminance on the focal plane of photoelectric equipment which represent the target and the background respectively were obtained; Finally, based on the atmospheric scintillation characteristics of the scattered radiation of reconnaissance satellites, using probability statistical theory and engineering experience analysis, it was pointed out that the decisive factor affecting the detection probability was the change in the target background contrast caused by the atmospheric scintillation, based on this, a new detection probability model of the optical reconnaissance satellite by ground optoelectronic equipment was proposed. The actual test data verifies that the calculated results of the model in this paper are in good agreement with the actual measured data.
Materials & Thin films
Image processing
Depth-rectified statistical scattering modeling for deep-sea video descattering
Fan Yihui, Jin Xin, Deng Rujia, Xie Jiayu, Sun Kelin, Yang Jingchuan, Zhang Bing
2022, 51(9): 20210919. doi: 10.3788/IRLA20210919
[Abstract](106) [FullText HTML] (42) [PDF 2011KB](45)
Deep-sea exploration is widely used in fields of environment and structural monitoring as well as exploration for oil and gas, which has attracted more attention in many countries of the world. In deep-sea exploration, the scattering phenomenon seriously reduces the visual image quality. Existing methods are limited in deep-sea scattering environments with multi-depth or non-uniform illumination. Thus, a deep-sea descattering method based on a depth-rectified statistical scattering model is proposed. The model proposed uses the transmission map to model the depth-constant scattered image, and uses the Gaussian statistical model to estimate the local scattering to obtain the depth-rectified scattering map in each color channel, so as to achieve the accurate modeling of scattering at multi-depth and non-uniform illumination scenarios. In order to demonstrate the effectiveness and robustness of proposed algorithm, we conducted tests on images of different scenes in shallow sea and deep sea, as well as on video sequences in deep-sea. Experimental results show that the proposed method outperforms existing methods in subjective quality and objective evaluation.
Semantic enhanced guide feature reconstruction for occluded pedestrian detection
Sun Xudan, Wu Qing, Zhao Chunyan, Zhang Mandun
2022, 51(9): 20210924. doi: 10.3788/IRLA20210924
[Abstract](92) [FullText HTML] (12) [PDF 1330KB](37)
In pedestrian detection, the inability to extract effective features due to pedestrians being severely occluded is one of the main reasons for missing pedestrian detection. To solve this problem, a semantic enhanced guided feature reconstruction algorithm for occlusion pedestrian detection is proposed. Firstly, the semantic feature enhancement module is designed based on the dependency between space and channel, and the global context information is established to enhance the feature of occlusion of pedestrians. Secondly, in order to focus on the visible area of pedestrians, the adaptive feature reconstruction module is used to generate the semantic segmentation map, and adaptively adjust the effective weight of the channel, enhance the distinguishability of pedestrians and background. Finally, the multi-level feature map is obtained by multi-level cascade two modules of semantic feature enhancement and adaptive feature reconstruction, and the multiple features are fusion for the final pedestrian analysis detection. On the challenging pedestrian detection benchmark CityPersons and Caltech, experimental results show that the proposed method achieves the missed rate of 47.28% and 44.04%, respectively, which effectively robust compared with other methods in the detection of occluded pedestrian.
Review of air moving target detection technology under environmental disturbance
Ren Weihe, Zhang Yue, Su Yun, Zhang Xuemin, Deng Hongyan, Liu Yi
2022, 51(9): 20210843. doi: 10.3788/IRLA20210843
[Abstract](220) [FullText HTML] (50) [PDF 2706KB](68)
Air moving targets such as stealth moving targets and high-speed aircraft have caused serious threats to the national security of all countries in the world, the detection of stealth moving targets and high-speed aircraft in the air is also a hotspot in the development of target detection technology around the world. This article describes a new type of target detection technology with better detection capabilities for air moving targets—environmental disturbance detection technology for moving targets in the air, and introduces the four main researches on airborne moving target environmental disturbance phenomena and their detection methods at this stage. That is, atmospheric disturbance field, plasma sheath, atmospheric polarization mode and wake, the detection principles and development status of the above four environmental disturbance detection technologies are studied, and the problems existing in the four environmental disturbance detection technologies in the air at the present stage are analyzed. Finally, the future development directions of the four technologies are prospected and summarized.
Shipboard sun-photometer image tracking system
Zhu Hai, Li Jianyu, Huang Honghua, Xu Gang, Sun Fengying, Wei Heli
2022, 51(9): 20210824. doi: 10.3788/IRLA20210824
[Abstract](60) [FullText HTML] (10) [PDF 2987KB](34)
Traditional sun-photometer cannot accurately track the sun on offshore mobile platform. In order to solve the problem of high-precision tracking of the sun in the process of ship moving, an image tracking system for shipboard sun-photometer(SSP) was constructed by using fisheye lens, gyro-stabilized platform and small-field CCD image sensor. The whole structure of the image tracking system of the shipboard sun-photometer and the design of the optical path of the single-arm probe were introduced. The coarse tracking of the sun in the large field of view by the clock method and fisheye imaging system was described in detail, and then the fine tracking measurement was carried out by the CCD image processing technology of small field of view. Besides, the software tracking algorithm, process and system tracking reliability were given. The image tracking system of shipboard sun-photometer can be automatically tracked and measured on offshore mobile platforms, and the comprehensive tracking accuracy was higher than 1′. The data were compared with the Japanese POM-01 MKⅢ sun-photometer. The results show that the maximum relative error of atmospheric transmittance at 940 nm band is less than 7.6%, and the maximum relative error of water vapor is less than 6.1%. The system can be applied to the shipboard sun-photometer to measure the atmospheric transmittance and water vapor at sea, and can also be used to track the sun on other moving unstable platforms.
Image recognition method of anti drone system based on coordinate attention mechanism
Xue Shan, Chen Yuchao, Lv Qiongying, Cao Guohua
2022, 51(9): 20211101. doi: 10.3788/IRLA20211101
[Abstract](106) [FullText HTML] (18) [PDF 2409KB](42)
Anti drone system is an effective way to identify and attack the "black flying" drone. Image recognition drone is one of the keys of anti drone system. Aiming at the problems that the samples collected from drones are small samples, the features are not enough and the recognition accuracy is not high enough, an image recognition method of anti drone system based on transfer learning, dense convolutional network and coordinate attention mechanism was proposed. Firstly, a variety of drone images in different backgrounds were collected by using self-made device, and data samples were set up; Secondly, the network TL-CA4-DenseNet-121 based on transfer learning, coordinate attention mechanism and dense convolutional network, the network TL-SE4-DenseNet-121 based on channel attention mechanism were designed to identify small samples. The designed network was used to identify small samples and compare. The network recognition experiment of coordinate attention module and channel attention module based on different positions and different numbers were carried out respectively; Finally, the network with the best recognition effect was compared with the classical convolutional neural network models. The experimental results show that the proposed TL-CA4-DenseNet-121 network has better recognition effect than other networks, and the average accuracy of recognition is 97.93%, F1-Score is 0.9826 and training time is 6832 s. It shows the superiority and feasibility of this network in identifying small sample drones.
Research on the classification of typical crops in remote sensing images by improved U-Net algorithm
Li Anqi, Ma Li, Yu Helong, Zhang Hanbo
2022, 51(9): 20210868. doi: 10.3788/IRLA20210868
[Abstract](171) [FullText HTML] (46) [PDF 1325KB](44)
Aiming at the problem of incomplete classification features of remote sensing images extracted by traditional algorithms and low accuracy of crop classification, we use drone remote sensing images as the data source and propose an improved U-Net model to classify and recognize crops such as barley, corn, etc. in the study area. In the experiment, the remote sensing image is preprocessed, and the data set is labeled and enhanced. Secondly, the algorithm is improved by deepening the U-Net network structure, introducing the SFAM module and the ASPP module, and using the multi-level and multi-scale feature aggregation pyramid method to construct an improved U-Net algorithm. Finally model training and improvement are completed. The experimental results show that the overall classification accuracy OA reaches 88.83%, and the combined ratio of MIoU reaches 0.52. Compared with the traditional U-Net model, FCN model and SegNet model, the classification index and accuracy are significantly improved.
Visual salient dim small target detection based on nonlinear anti noise estimation
Chen Shiqiong
2022, 51(9): 20210939. doi: 10.3788/IRLA20210939
[Abstract](112) [FullText HTML] (22) [PDF 1400KB](38)
Aiming at the importance and key of dim small target detection in infrared image processing technology, a detection algorithm based on nonlinear anti noise estimation is proposed to solve the problem of dim small target detection with high reliability and robustness. Based on the traditional visual saliency algorithm and spatial distance processing method, the proposed method uses the nonlinear weighting method to estimate the target and background area. On the basis of not significantly reducing the signal-to-noise ratio of the target signal, the influence of isolated small noise points on the performance of the detection algorithm can be weakened, and the anti-noise performance can be improved. Firstly, the background is predicted by modular and nonlinear mapping, and then the distance correlation factor is integrated to filter out the noise interference. Finally, the binary threshold segmentation is carried out on the processed image to automatically detect and output the target position information to the next level processing software. The experimental results show that the proposed algorithm can obtain a higher detection rate on the subject test curve under the same false alarm rate and significantly suppress the background noise compared with the advanced weak and small target detection algorithm in recent years; On the test comparison data of local signal-to-noise ratio and background suppression factor, the proposed algorithm can obtain higher detection indexes. The disadvantage is that the algorithm adopts nonlinear processing technology and has low operation efficiency. It needs to further optimize the algorithm to improve the calculation speed and realize the real-time target detection of the algorithm.
Optical fiber sensing recognition algorithm based on deep neural network
Li Dongliang, Lu Bei
2022, 51(9): 20210971. doi: 10.3788/IRLA20210971
[Abstract](137) [FullText HTML] (32) [PDF 1414KB](43)
In order to solve the problem of reducing the recognition probability caused by the aliasing of different types of event signals in the optical fiber sensing process, a dual optical fiber sensing structure using differential correlation calculation is built. On this basis, a signal recognition algorithm based on deep neural network is proposed. First, the echo signal of the dual fiber is used to calculate the correlation coefficient. Then, the threshold range is set by signal characteristics of different event types, so as to improve the signal-to-noise ratio through correlation calculation and threshold filtering. A deep neural network model with three hidden layers is designed, and the purpose of low-frequency noise suppression and signal aliasing demodulation is accomplished by separating the input layer and the related operation layer. The experiments separately test three common intrusion events. The recognition probability of combined events by different algorithms is analyzed. The results show that the echo spectrum shape of the three events has significant characteristics. The recognition probability of the three algorithms is more than 95% for a single trigger event, and the average recognition value of this algorithm is 98.5%. When two events are triggered at the same time, the average recognition probabilities of the three algorithms are 73.4%, 84.5%, and 96.4%, respectively. When three events are triggered at the same time, the average recognition probabilities of the three algorithms are 65.2%, 78.3%, and 93.5%, respectively. It can be seen that this algorithm has a better recognition effect when there is interference and aliasing of signals in optical fiber sensing.
Point cloud target recognition algorithm based on stereo vision and feature matching
Wang Xiaoyan, Xu Gaokui
2022, 51(9): 20210596. doi: 10.3788/IRLA20210596
[Abstract](130) [FullText HTML] (23) [PDF 1190KB](40)
Accurately extracting the point cloud collection of the target to be measured in the three-dimensional point cloud data is a key issue of the three-dimensional point cloud target recognition technology, and it is also an important challenge in the field of target recognition from 2D to 3D in recent years. The main difficulty is to quickly find the correlation function relationship between discrete point clouds. Combining stereo vision and feature matching, a constraint mechanism of target point cloud that can characterize different field of view conditions is constructed, and the original feature matching algorithm is optimized by using stereo vision as the constraint condition. An estimation algorithm based on stereo vision is designed, and recognition rules under different selection ratios are obtained through training and learning. The experiment uses ARIES Lidar to collect point clouds, and selects three typical target states through MATLAB. When the target discrimination is high, the target recognition rate before and after optimization is above 98%. When the target discrimination is low, the restriction conditions of the target boundary after optimization can improve the recognition probability. The position deviation of the optimized point cloud data can reach 0.55 mm, which is 0.19 mm higher than 0.74 mm before optimization. At the same time, the convergence time curve of the optimized algorithm is better than before optimization. The average convergence time above 3000 points is about 8.33 s, which is better than 12.76 s before optimization. In summary, the optimized algorithm has better recognition efficiency.
Infrared technology and application
Study on large-area array SW HgCdTe infrared focal plane device
Gong Xiaodan, Li Hongfu, Yang Chaowei, Yuan Shouzhang, Feng Yuanqing, Huang Yuanjin, Hu Xu, Li Lihua
2022, 51(9): 20220079. doi: 10.3788/IRLA20220079
[Abstract](305) [FullText HTML] (75) [PDF 1929KB](123)
With the development of infrared focal plane technology, large-area infrared focal plane devices have been widely used in remote sensing, meteorology, resource surveys and high-resolution earth observation satellites. Therefore, based on the third-generation infrared focal plane technology ultra-large-scale focal plane devices are called research hotspots at home and abroad. The short wave (SW) 2 k (18 μm, pixel pitch) mercury cadmium telluride(MCT) infrared focal plane device was reported, which was successfully developed by Kunming Institute of Physics using n-on-p technology. The SW 2 k MCT infrared focal plane device has broken through the preparation of large-size cadmium zinc telluride (CdZnTe) substrates and the growth of large-area liquid phase epitaxy thin film materials. The substrate size was increased from Φ75 mm to Φ90 mm, and a highly uniform large-area Mercury Cadmium Telluride (HgCdTe) thin film material was obtained. By tackling key technologies such as large array device technology and large area array flip-chip interconnect, a high-performance SW 2 k×2 k (18 μm) MCT infrared focal plane device with an operability over 99.9%, average peak detection rate (D*) greater than 4×1012 (cm·Hz1/2)/W and dark current density of 1 nA/cm2 was finally obtained.
Design and fabrication of short and middle wavelength infrared dual band-pass filter at cryogenic temperature
Zhou Sheng, Liu Dingquan, Wang Kaixuan, Li Yaopeng, Hu Jinchao, Wang Shuguang, Zhu Haoxiang
2022, 51(9): 20210964. doi: 10.3788/IRLA20210964
[Abstract](178) [FullText HTML] (40) [PDF 2081KB](69)
Dual band-pass filter can simultaneously form two spectral channels to transmit at any position of the element, so as to realize simultaneous detection of dual spectral channels. In this paper, an infrared dual band-pass filter used at 100 K temperature was developed. Sapphire (Al2O3) was used as substrate, and Ge and SiO were used as high (H) and low (L) refractive index thin films respectively. An infrared dual band-pass filter combined with a shorter wavelength channel (2.60-2.85 μm) and a longer wavelength channel (4.10-4.40 μm) was designed and fabricated. Based on Fabre-Perot (F-P) filter structure, Ge and SiO thin films were deposited by electron beam evaporation and resistance thermal evaporation on the two sides of the substrate. At the working temperature (100 K), the filter transmittance of shorter channel is 91.2%, and the top ripple amplitude is 2.1%; the average transmittance of longer channel is 87.7%, and the top ripple amplitude is 3.8%. Between the two channels (wavelength 3.00-3.95 μm), the cut-off depth is less than 0.1%. The optical performance of the infrared dual band-pass filter can meet the spectral requirements and contribute to more accurate infrared remote sensing and detection.
Numerical study of fluid flow, heat transfer and infrared signature of 2D exhaust system model with full shielded guide vane combined with rear body
Cheng Wen, Ji Honghu, Shi Xiaojuan, Wang Hao
2022, 51(9): 20210965. doi: 10.3788/IRLA20210965
[Abstract](106) [FullText HTML] (23) [PDF 3412KB](39)
In order to reduce the contribution of the last-stage turbine of the infrared radiation in backward of the exhaust system, the full shielding guide vane(FSGV) is designed to achieve full shielding of the low-pressure turbine. Numerical simulation methods are used to study fluid flow heat transfer and infrared signature of three exhaust system (including baseline axisymmetric exhaust system,2D exhaust system and 2D exhaust system with FSGV) models combined with aircraft rear body, revealing the general rule of infrared radiation characteristics in the 3-5 μm band in backward of the three different combined models; the results show that compared with the baseline axisymmetric exhaust system model combined with aircraft rear body, whether it is a 2D exhaust system model combined with aircraft rear body or 2D exhaust system model with FASG model combined with aircraft rear body, the infrared radiation intensity has been reduced, and the drop rates are 22.1% and 46.9% respectively at a detection angle of 0°. If the cooling technology is adopted for the FSGV, as long as cooling efficiency reaches 0.282 and 0.482, compared to uncooled state of the exhaust system, the infrared radiation in backward of the exhaust system can be reduced by 20.4% and 35.45%.
Quality assessment of FY-4 A’s geostationary interferometric infrared sounder observations data
Wang Yurun, Guan Li
2022, 51(9): 20210838. doi: 10.3788/IRLA20210838
[Abstract](165) [FullText HTML] (68) [PDF 1917KB](34)
The quality assessment of FY-4A Geostationary Interferometric Infrared Sounder (GIIRS) observation data can promote its application in numerical weather forecast. Using FY-4A Geostationary Interferometric Infrared Sounder (GIIRS) observation data in July 2020, this paper not only analyzes the dependence on FOV and latitude of noise for all channels of GIIRS, but also analyzes the distribution of bias (observation minus model) with time, FOV, latitude and zenith angle to evaluate the quality of GIIRS observation data. The results show that the noise of GIIRS exceeded the sensitivity index in the bands 727.5-733.8 cm−1, 1107.5-1130 cm−1, 1650-1776.9 cm−1, and the biases and standard deviation of biases of these three bands are obviously larger than other channels. Except for the channels with large noise in long wave, the noise of each column is small in the middle and larger on both two sides when the noise of all bands is arranged in a 32×4 area array. Besides, the distribution of NEdT does not vary with latitude and FOR. So, when GIIRS data assimilation or variational inversion is carried out, the observation error can just consider the NEdT distribution of different channels in 32×4 array. The surface temperature of the numerical prediction model is underestimated in the daytime, which makes the underestimation of simulated radiation, reduces the absolute value of the bias, and makes the bias have obvious diurnal variation. The bias characteristics of middle-wave channels basically do not vary with the columns of 32×4 array, and are mainly related to the rows in the array. The bias correction can be carried out for the rows of 32×4 array, and the correction of latitude band and satellite zenith angle is basically not needed.
Research on early warning and detection capability of scanning camera of space-based infrared system
Lei Ping, Xing Hui, Wang Juanfeng, Wang Bing, Huang Ligang, Wang Jinsuo
2022, 51(9): 20210977. doi: 10.3788/IRLA20210977
[Abstract](272) [FullText HTML] (47) [PDF 1241KB](91)
With the completion of the deployment of the fifth geostationary satellite in May 2021, all satellites of the entire space-based infrared system are nearly depolyed, and the system's ability to monitor the ground is greatly improved. Based on a large number of relevant literature and public reports, a comprehensive performance analysis of the scanning cameras of all 9 orbiting satellites of the space-based infrared system is carried out. First of all, according to the detector system of the scanning camera and flight-trace characteristics, this paper analyzes its scanning imaging system and calculates estimated values of such key parameters as optical system parameters, detector parameters, ground resolution and sensitivity of all 9 orbiting satellites' scanning cameras. Secondly, to comprehensively analysis and research on the flight characteristics of space-based infrared system satellites in large elliptical orbits and their ground surveillance missions, this paper proves that the optimal in-orbit operation mode is pairwise synchronization, and the difference between the two satellites in a single orbit is 1/4 period. A comprehensive analysis of the flight characteristics and ground monitoring missions of the space-based infrared system geostationary satellites shows that at least two satellites are in good ground observation positions in the mid-latitudes of the northeastern hemisphere. Finally, according to the radiation characteristics of the ballistic missile plume and the detection parameters of the space-based infrared system scanning cameras, the minimum observation height of the missile plume by all orbiting satellites is calculated and analyzed. The results show that the 40°N latitude area in the Eastern Hemisphere can be monitored by more than 4 satellites at the same time, and some satellite-borne cameras have the ability to detect the ignition timing of ballistic missiles.
Special issue—Ultra precision manufacture and testing technology of optical aspheric surface
Current situation and development trend of aspheric optical surface defect detection technology (invited)
Li Mingze, Hou Xi, Zhao Wenchuan, Wang Hong, Li Mengfan, Hu Xiaochuan, Zhao Yuancheng, Zhou Yang
2022, 51(9): 20220457. doi: 10.3788/IRLA20220457
[Abstract](354) [FullText HTML] (84) [PDF 6810KB](137)
Aspheric optical elements have greater freedom and flexibility, and are widely used in aerospace, microelectronic equipment, optical precision measurement, laser optics and many other fields. The surface defects of optical elements will affect the performance of optical systems, and the control of surface defects requires corresponding detection methods. There are still technical challenges in the detection of optical surface defects with high resolution, high accuracy and high efficiency. This paper summarizes the types, evaluation standards and detection methods of surface defects of optical elements, focuses on the surface defect detection technology of aspheric optical elements and its application range, analyzes and compares the advantages and disadvantages of various methods, and finally prospects the development trend of surface defect detection technology.
Reduction of grid effect in ultra-light mirror machining by inflatable balanced method (invited)
Yu Qiuyue, Zhou Xiaohua, Wang Guoyan, Qiao Guobao, Lv Tianbin, Zhang Zhaojian, Wang Jinghua, Shao Jianye, Cheng Yuntao
2022, 51(9): 20220389. doi: 10.3788/IRLA20220389
[Abstract](121) [FullText HTML] (14) [PDF 2764KB](37)
For the mirror with traditional honeycomb sandwich structure, due to the existence of grid effect in the processing, the thickness of the mirror panel and the honeycomb size are correlated with each other, which seriously affects the lightweight design of the mirror. Aiming at the ultra-light mirror with honeycomb sandwich structure, an inflatable balanced processing method to reduce the grid effect was proposed. By using the control variable method to design test, the changes of grid effect under normal processing and inflatable balanced processing were compared. The experimental results show that when the mirror surface precision RMS reached more than 1/10λ (λ=632.8 nm), there is an obvious grid effect in the normal processing without inflation, but not in the inflatable balanced processing. It could be seen that inflating the inside of the mirror could effectively balance the processing pressure and make the deformation of the reinforced area and the non-reinforced area tend to be the same during processing, so as to effectively reduce the grid effect.
High-efficiency and high-quality combined polishing method of zinc selenide crystal (invited)
Yang Chao, Zhang Naiwen, Bai Yang
2022, 51(9): 20220531. doi: 10.3788/IRLA20220531
[Abstract](166) [FullText HTML] (42) [PDF 1798KB](46)
As an excellent infrared crystal material, zinc selenide crystal is widely used in infrared optical systems. In order to improve the processing quality and processing efficiency of zinc selenide crystal, a method combining magnetorheological polishing (MRF) and traditional numerical control polishing (CCOS) technology was proposed, and the magnetic current of zinc selenide crystal was configured through multiple sets of orthogonal experiments. Change the polishing liquid, carry out magnetorheological polishing on a zinc selenide crystal with a diameter of 50 mm, and then perform traditional numerical control polishing on the surface traces after magnetorheological polishing. The positive pressure is in the range of 0.05-0.1 MPa. Uniform polishing after 30 minites, the surface roughness of the zinc selenide crystal was reduced from 3.832 nm to 1.57 nm, and the roughness was significantly improved. The method effectively improves the processing efficiency of aspheric zinc selenide crystals and improves the surface quality after processing, and has important reference value for aspheric ultra-precision processing of zinc selenide crystals.
Combined fabrication of high order off-axis convex aspheric mirror (invited)
Peng Lirong, Cheng Qiang, Zeng Xuefeng, Zhou Xiaoqin
2022, 51(9): 20220611. doi: 10.3788/IRLA20220611
[Abstract](109) [FullText HTML] (16) [PDF 2783KB](47)
In order to improve the manufacturing accuracy and efficiency of the secondary mirror in the off-axis three mirror anastigmatic (TMA), the combined fabrication and testing technologies of the off-axis convex aspheric mirror were studied. Firstly‚ the optical parameters, technical specifications and overall processing route of square (298 mm×264 mm) high order off-axis convex aspheric mirror were introduced. Then, the grinding processing strategy and the combined processing technology based on bonnet and pitch polishing were presented. At last, offner-type compensator was used to meet the back transmission null lens testing in the polishing stage, and then the surface distortion was corrected by ray tracing method, the final RMS value was 0.025λ (λ=632.8 nm), which meet the target requirements. The above combined processing technology and back transmission null lens testing detection scheme can significantly improve the processing accuracy and efficiency of off-axis convex aspheric mirror.
Method of edge control on surface error in aspherical optics (invited)
Wu Lunzhe, Xu Xueke, Wu Lingqi, Wang Zhe
2022, 51(9): 20220602. doi: 10.3788/IRLA20220602
[Abstract](109) [FullText HTML] (8) [PDF 2211KB](39)
Computer Control Optics Surfacing (CCOS) requires the surface error map for iterative processing to get low error by dwellingtime caculation. Because the smaller aperture of error map will be gotten in interferometer on edge of optic work part, so the predictive extrapolation of surface error map is the basic technology of magneto-rheological polishing, ion beam polishing and other machining methods. Based on the similarity of surface error and the continuity of edge error, the extrapolation of surface error method was developed, based on Zernike fitting and Laplace equation. The theory was studied and the algorithm was developed to get extrapolation of surface error map, fulfilling the similarity and the continuity. The result was evaluated by surface error comparison and residual error calculation, which was proved to be effective.
Small-scale cluster damage mitigation and detection on fused silica surface (invited)
Shi Feng, Qiao Shuo, Deng Mingjie, Song Ci, Tie Guipeng, Tian Ye, Hao Qun, Wang Shanshan, Zhou Haifeng, Chen Jian, Sun Guoyan, Shen Xiao
2022, 51(9): 20220539. doi: 10.3788/IRLA20220539
[Abstract](159) [FullText HTML] (29) [PDF 4546KB](45)
Aiming at the problem that the existing small-scale cluster damage mitigation and detection technology is still imperfect, it focuses on the multi-modal in-situ detection method of sub surface defects, and systematically measures and analyzes the number and size of surface damage of damaged samples, the morphology of typical small-scale damage, light and heat absorption, fluorescent area and other indicators, and carries out magnetorheological repair research. The results show that the absorbent impurities inside the small-scale damage of fused silica are the main factors affecting the performance of the components. Before the magnetorheological ribbon contacts the bottom of the damage, the overall absorption and fluorescence distribution of the damage show an upward trend. The damage irradiation process of high repetition rate laser after magnetorheological repair is a process from slow to fast, from impurity to body, and gradually expanding outward from the edge. It can effectively repair the surface after magnetorheological repair, and can be used as the third process of combined repair process. The research results provide a reference for the construction of optical element detection and characterization system.
High precision manufacturing and testing of large aperture silicon-based space infrared lens (invited)
Wang Guoyan, Xu Rui, Yu Qiuyue, Wang Yonggang, Meng Xiaohui
2022, 51(9): 20220427. doi: 10.3788/IRLA20220427
[Abstract](142) [FullText HTML] (14) [PDF 2548KB](46)
With the development of infrared technology, the demand for large aperture space infrared optics is increasing. Their manufacturing indexes are approaching the manufacturing requirements of visible optics gradually, which poses a higher challenge to the processing and testing technology of new infrared optics. A processing scheme of ultrasonic milling, robot griding and ion beam polishing was proposed for the manufacturing of large diameter ultra-thin silicon-based infrared lens with high gradient. This method overcame the defects of low efficiency and high frequency surface error caused by single process. In order to avoid the testing error caused by supporting force in contour testing of the aspherical convex side, flexible buffer supporting and three-point forced displacement supporting were applied in rough and fine polishing phases respectively, which effectively solved the supporting deformation problem in the testing of large aperture and high gradient ultra-thin lens. Through theoretical simulation and experimental verification, it was proved that the testing method had good consistency. An improved contour detection method was adopted to achieve accurate separation of supporting error in contour testing, and has effectively improved the limit accuracy of manufacturing. Finally, the machining accuracy of convex aspheric surface with large diameter mm infrared lens reached RMS λ/50 (λ=632.8 nm), which satisfied the design requirements.
Sub-aperture stiching and CGH mixed compensation for the testing of large convex asphere (invited)
Su Hang, Wang Xiaokun, Cheng Qiang, Li Lingzhong, Wang Jing, Li Wenyan, Wu Qiong, Tang Wa, Luo Xiao, Zhang Xuejun
2022, 51(9): 20220576. doi: 10.3788/IRLA20220576
[Abstract](144) [FullText HTML] (36) [PDF 4711KB](59)
In order to achieve high-precision testing of large convex asphere, a testing method combining sub-aperture stitching and computer generated hologram compensation is proposed. Because the asphericity of the center is small, the direct testing method of spherical wave is used; while the asphericity of the outer ring is large, the method of sub-aperture stitching and computer generated hologram (CGH) mixed compensation is used for measurement. Then, the center testing data and the outer ring testing data are stitched by the stitching algorithm to obtain the full-aperture surface shape. Combined with an example, a large convex asphere with a diameter of 540 mm is measured. The test results were compared with the Luphoscan testing results. The residual error of the two methods to test the RMS value of the surface is 0.019λ, and RMS value after subtracting the self-test aperture and stitching result point-to-point is 0.017λ. The results show that the method can achieve high-precision testing of large convex asphere.
High-precision shape measurement technology for convex aspheric with small aperture and large convex asphericity
Liu Jiani, Chen Anhe, Li Zhiyong, Xia Fangyuan, Liu Bingcai, Li Shijie
2022, 51(9): 20220190. doi: 10.3788/IRLA20220190
[Abstract](123) [FullText HTML] (17) [PDF 2868KB](66)
Convex aspherical mirrors are widely used in reflective optical systems, but high-precision shape measurement technology is always a difficult problem in optical manufacturing. In order to achieve high- precision detection of convex aspheric with small aperture and large asphericity, a null test interference detection technique based on computer generated hologram (CGH) was proposed. Firstly, the detection principle and method of this technology were described in detail, and the key technical points in the processing of testing CGH and alignment CGH design were given. Then, combined with engineering application, the corresponding CGH was designed and manufactured for convex aspheric with the aperture of 15 mm, the vertex curvature radius of 11.721 mm and its asphericity of 72 μm, and the null test interference detection experiments based on CGH were completed. Finally, the accuracy of the proposed method was verified by cross-comparison with Luphoscan detection technique. This technology provides an effective method for high-precision testing of small aperture convex aspheric and has significant engineering application value.
Interferometric testing of convex freeform surface in industrial lens based on Computer-Generated-Hologram (invited)
Zhu Deyan, Tang Junwei, Guo Chengli, Li Yuanzheng, Zhao Liefeng
2022, 51(9): 20220456. doi: 10.3788/IRLA20220456
[Abstract](183) [FullText HTML] (17) [PDF 2468KB](42)
Industrial lens elements have small aperture, large quantity and high precision requirements. Using free-form surface on the convex surface of lens will lead to complex surface shape and large deviation, which poses a high challenge of surface testing. An interferometric testing based on CGH was proposed. By using the Zemax software, we optimized the optical design, established the model to analyze the influence by the calibrating errors of industrial lens, and proposed an interferometric testing scheme of industrial lens. An experiment by testing a freeform surface of industrial lens was provided to demonstrate the reliability of the model and scheme. The experimental results show that CGH can realize the full aperture interference testing of convex free-form surface industrial lens, and the testing result is 0.57 μm PV which meets the needs of lens testing and verifies the reliability of interferometry by comparing with profilometer.
Long focal length aspherical mirror testing with CGH and auxiliary lenses (invited)
Zhang Yuxin, Li Fazhi, Yan Lisong, Yan Dong, Wang Chaofan, Zhang Yuhe, Zhang Binzhi, Zhang Xin, Cai Mingxuan, He Junchao, Wang Xiaokun
2022, 51(9): 20220384. doi: 10.3788/IRLA20220384
[Abstract](186) [FullText HTML] (30) [PDF 1830KB](46)
At present, the radius of curvature of the primary mirror in some large-aperture optical telescopes has reached the order of tens of meters. If the surface of the mirror is tested simply by CGH, the length of the testing optical path is not lower than the length of its radius of curvature. Due to factors such as site size and ambient airflow disturbance, it is difficult to achieve high-precision measurement of the mirror surface under these conditions. In order to solve the problem of high-precision surface testing of large-aperture long focal length optical mirror, a hybrid compensation method is proposed. This hybrid compensation method combines CGH and auxiliary lenses to effectively shorten the length of the testing optical path, and can realize null testing of aspherical mirrors. In the optical path design, it is necessary to effectively optimize the optical design parameters of the hybrid compensation optical path and the separation of the CGH diffraction order. At the same time, the optical path length should be less than the radius of curvature of the aspherical mirror to achieve the purpose of shortening the length of the testing optical path. By testing the EELT main mirror, the simulation test shows that the testing path length of the method can be shortened to less than 1/8 of the length of the radius of curvature of the surface. Designing testing accuracy is better than that of RMS λ/100 (λ=632.8 nm). The above simulation results show that this method can not only realize the shortening the length of the testing optical path, but also achieve the high-precision surface testing of the aspherical mirror.
Testing of aspheric surface with low reflectivity using hybrid type computer-generated hologram (invited)
Guo Chengli, Zheng Dekang, Zhu Deyan, Yang Xiaofei, Li Yuanzheng, Zhang Jian, Zhao Liefeng
2022, 51(9): 20220547. doi: 10.3788/IRLA20220547
[Abstract](185) [FullText HTML] (36) [PDF 2237KB](38)
Computer-generated hologram (CGH) is widely used in high-precision off-axis aspheric surface testing. In order to improve the fringe contrast in the testing process of materials with low reflectivity, a hybrid type computer-generated hologram is proposed. The alignment area uses a reflective hologram, the optimal contrast corresponding to the film reflectivity is derived based on diffraction efficiency model, the main area applies phase type CGH to achieve diffraction efficiency improvement, thereby improving the fringe contrast of the detection area. The processing of hybrid hologram is realized by multi-step photo lithography process, and the off-axis aspheric surface of glass-ceramics material is tested using the fabricated CGH. The experimental results show that the hybrid type CGH can obtain clear fringe contrast, and the final detection accuracy is better than 0.02λ(λ=632.8 nm). The proposed hybrid type CGH can be widely used in the testing of aspheric surfaces with low reflectivity material.
Virtual-real combination interferometry for aspheric surface parameter error measurement with cat-eye-wavefront positioning (invited)
Hu Yao, Tao Xin, Hao Qun
2022, 51(9): 20220497. doi: 10.3788/IRLA20220497
[Abstract](140) [FullText HTML] (28) [PDF 2425KB](36)
Aspheric surfaces are widely used in optical systems. Aspheric surface parameters, including vertex radius of curvature, conic constant, and high-order aspheric coefficients participate in optical design, manufacture, measurement, alignment and assembly. Precision measurement for aspheric surface parameters is the basis for manufacture, alignment and assembly. A partial compensation measurement system is proposed based on virtual-real combination interferometer for aspheric surface parameter error measurement. In this measurement system, residual wavefronts are measured by partial compensation interferometry. The interferometer is multiplexed in cat-eye-wavefront positioning method to measure the compensation distance which is the distance between compensator and aspheric surface under test. Aspheric surface parameter errors are calculated by virtual-real combination iterative algorithm. The system only needs to introduce a converging lens into the optical path of partial compensation interferometry, which is easy to align and assemble, and has high measurement accuracy. The effectiveness and accuracy are verified through the measurement of a 4th-order aspheric surface.
High-precision profile measurement method for axisymmetric aspheric mirror (invited)
Fan Xinrui, Diao Xiaofei, Wu Jianwei, Kang Yanhui
2022, 51(9): 20220500. doi: 10.3788/IRLA20220500
[Abstract](109) [FullText HTML] (11) [PDF 1829KB](42)
In order to achieve the goal of high-precision and traceable aspheric surface profile measurement, a mathematical model of the measurement trajectory is established for the surface profile measurement of axisymmetric aspheric mirrors, and a non-contact coordinate scanning measurement method with independent metrology loop is proposed. The method applies a separated metrology frame, which effectively reduces the influence of each motion module on the measurement accuracy of the system during the measurement process; the probe adopts a four-quadrant interferometry system with integrated array waveplates, which improves the dynamic performance of the probe and is more conducive to the measurement of complex aspheric surface shapes; the motion module with a common reference between the scanning actuator and the multiplexed laser interferometry system is designed to track the position information of the scanning motion mechanism in real time, which improves the accuracy of the scanning motion and enables the measurement of the surface shape. The scanning actuator is designed to track the position information of the scanning motion mechanism in real time to improve the accuracy of the probe motion and make its measurement value traceable to the definition of "meter". The measurement device is built and the surface profile of the standard sphere and aspheric mirror are measured separately. The test results show that the measurement error is less than 0.2 μm and the repeatability accuracy was 70 nm, and the system measurement accuracy reaches submicron level.
Full-field heterodyne phase shifting two-wavelength interferometry surface testing technologies
Fan Guoxiang, Li Yang, Zhang Wenxi, Wu Zhou, Lv Tong
2022, 51(9): 20220118. doi: 10.3788/IRLA20220118
[Abstract](141) [FullText HTML] (16) [PDF 3936KB](47)
Because of its high dynamic range and high accuracy, two-wavelength interferometry has great potential, but there are some problems with the use of piezoelectric phase shifting technology, compared with the conventional piezoelectric phase shifting technology, in full-field heterodyne phase shifting technology, the heterodyne light source with low frequency difference can easily realize multi-step phase shifting algorithm, simplify the procedure of phase shifting, ensure the phase shifting accuracy of different wavelengths at the same time. A full-field heterodyne two wavelength phase shifting interferometry is proposed and a full-field heterodyne two wavelength phase shifting interferometer system is built, an aspheric mirror with maximum deviation of 13 μm at the edge and a step with a height of (1.3±0.1) μm is tested. With some experiment tests, the PV error is λ/3.53 at 633 nm wavelength, the PV repeatability is λ/77.38, the RMS error is λ/14.16, the RMS repeatability is λ/919.10 when testing the aspheric mirror and the height error is λ/16.19, the height repeatability is λ/311.85 when testing the step.
Adaptive cyclic compensation structure used in freeform surface interferometric testing
Liu Renhu, Wu Jinling, Cao Jiaquan, Wu Shengyang, Zhou Sheng, Yu Benli, Zhang Lei
2022, 51(9): 20220157. doi: 10.3788/IRLA20220157
[Abstract](116) [FullText HTML] (23) [PDF 2123KB](50)
In order to alleviate the inherent contradiction of existing deformable mirror (DM)-based adaptive freeform surface interferometers, which can not take into account both large departure coverage and DM surface monitoring, therefore, adaptive ring-cavity compensator (ARCC) was proposed, which can generate large departure wavefront using DM deformation multiple times, and it had been preliminarily verified. Considering the practical application of ARCC and the fact that most freeform surfaces in optical systems were low-order aberration surfaces, the low-order aberration compensation characteristics of ARCC were verified and studied. Firstly, the compensation capability of ARCC and TSRC (traditional single round compensator) for astigmatism, coma and spherical aberration was compared by Zemax modeling. It was concluded that the ability of ARCC to compensate astigmatism and coma were about twice that of TSRC, and the ability of ARCC to compensate spherical aberration was also significantly greater than TSRC, which verified the advantage of ARCC in low-order aberration compensation; Secondly, the low-order aberration compensation of ARCC was studied, and it was include that the aberration types on DM in ARCC structure was one-to-many or many-to-one with the aberration types compensated to the tested surface. The results show that in practice, four low-order aberration free-form surfaces are compensated and verified by using ARCC and TSRC respectively. Under the same DM stroke variable, ARCC shows more excellent low-order aberration compensation ability than the TSRC.
Lasers & Laser optics
Study on mid-infrared optical parametric oscillator based on MgO:PPLN pumped by narrow linewidth 1064 nm fiber laser
Li Bingyang, Yu Yongji, Wang Zijian, Wang Yuheng, Yao Xiaodai, Zhao Rui, Jin Guangyong
2022, 51(9): 20210898. doi: 10.3788/IRLA20210898
[Abstract](183) [FullText HTML] (32) [PDF 1804KB](37)
A 3.83 μm mid-infrared optical parametric oscillator based on 1064 nm Yb-doped fiber laser pumped MgO:PPLN is proposed. Based on the threshold theory of single resonant optical parametric oscillator and the beam energy concentration theory before and after linewidth narrowing, the effects of the beam distribution in the resonant cavity and the different energy concentration levels before and after linewidth modulation on the threshold and optical-optical conversion efficiency under different pump beam focusing depths are analyzed. By using a single fiber Bragg grating to narrow the pump light width, the influence of the pump light width on the output characteristics of the mid-infrared optical parametric oscillator is analyzed under different duty ratios. When the pump power is 18 W, the pulse laser duty cycle is 0.2%, the pulse width is 100 ns, and the pump light width is 2.5 nm, the MgO:PPLN mid-infrared optical parametric oscillator obtains 3.83 μm laser output with a power of 1.42 W, and the optical-optical conversion efficiency is 7.9%. When the linewidth is narrowed to 0.1 nm and the pulse width is 2 ns, the infrared optical parametric oscillator in MgO:PPLN achieves 3.83 μm laser output with the highest power of 1.98 W. The optical-optical conversion efficiency is 11% and the beam quality M2=1.89. At the same time, the laser output efficiency is increased by 39.2% compared with that before linewidth narrowing.
Research on mid-infrared laser at 35 kHz based on optical parametric oscillator
Jiang Xingchen, Cheng Dehua, Li Yeqiu, Cui Jianfeng, Dai Qin
2022, 51(9): 20210817. doi: 10.3788/IRLA20210817
[Abstract](103) [FullText HTML] (9) [PDF 1451KB](32)
A 3.8 μm periodically poled LiNbO3 optical parametric oscillator based on high repetition frequency pumping is studied. The Nd:YVO4 acousto-optic Q-switched laser is used, obtaining a fundamental 1064 nm laser with good beam quality, the repetition frequency at 25-35 kHz, the maximum average power of 6.1 W and the pulse width of 59.1 ns. The temperature tuning characteristic of MgO:PPLN crystal with the period Λ=29.5 μm under the 1064 nm laser pumping is simulated. Through experiments, the 3599.6-3845.5 nmmid-infrared laser is obtained at a temperature of 25-200 ℃. When the temperature of the PPLN crystal is 30 ℃and the pump power is 6.1 W, the mid-infrared laser is obtained with the maximum output power of 0.45 W and the repetition frequency of 35 kHz at 3845.5 nm.
Small scale optical receiver of spaceborne Doppler wind lidar
Chu Jiaqi, Han Yuli, Sun Dongsong, Zhao Yiming, Liu Hengjia
2022, 51(9): 20210831. doi: 10.3788/IRLA20210831
[Abstract](110) [FullText HTML] (13) [PDF 3367KB](47)
Spaceborne wind lidar is considered to be the best means of wind field observation due to its real-time, high-precision and high resolution. Researches on spaceborne Doppler wind lidar have been actively carried out in China. The direct detection receiver of Doppler wind lidar developed for the satellite orbit with an altitude of 400 km is introduced. The receiver employs the dual Fabry-Perot etalons as the discriminating frequency unit and its parameters are specially designed for the spaceborne application. The main optical elements of the receiver are connected by molecular force and reversely inserted into the fillister of the receiver shell. The structure of the receiver is stable, reliable and highly integrated with the size of 450 mm×300 mm×80 mm, adapting to the spaceborne requirements of stability and small scale. The Fabry-Perot etalon transmission curves are obtained by tuning the wavelength of laser and the parameters of transmission curves are tested and analyzed. The wind measurement performance of the optical receiver is simulated according to the actual measured parameters. The simulation results show that the maximum wind velocity error is 2.94 m/s at the height of 30 km. Then the influence of the receiver bandwidth on measurement accuracy is further analyzed. The analysis results show that when the bandwidth deviation is 0.43 pm, the measurement error increment of 1m/s is caused.
Laser fuze anti-interference method based on array laser echo waveform feature recognition
Meng Xiangsheng, Li Jing, Li Lekun, Li Tie
2022, 51(9): 20210837. doi: 10.3788/IRLA20210837
[Abstract](95) [FullText HTML] (21) [PDF 6873KB](30)
Aiming at the problem that the laser fuze is easily interfered by cloud, fog and other aerosol environment, an anti-interference method based on the array laser echo waveform feature recognition is proposed. According to the scattering theory of pulsed laser in aerosol environment, the influence of pulse width and field angle on target recognition is analyzed. The time domain characteristics of target waveform in interference environment are simulated, and the simulation results are verified. Based on the characteristics of echo waveform, a detection system scheme of narrow field array laser echo feature digital recognition is designed, and the target and cloud echo array data with 2° resolution are obtained by virtual prototype simulation technology. The results of analysis indicate that the extreme value and mean value of pulse amplitude variance of target echo array are larger than that of cloud, and the method based on array laser echo waveform feature can effectively improve the anti-interference performance. The simulation and measured results provide theoretical and experimental basis for the effectiveness of the anti-jamming method based on array laser waveform recognition.
Study on application of laser-induced breakdown spectroscopy in impurity measurement of lead-based reactor
Sun Zhaoxuan, Hu Chen, Zeng Xian, Gao Xinxin, Zhang Yong, Wang Xi, Wang Qingsheng
2022, 51(9): 20210855. doi: 10.3788/IRLA20210855
[Abstract](135) [FullText HTML] (27) [PDF 2164KB](21)
Lead-based reactor is rated as the first fourth-generation reactor expected to achieve commercial application by Generation IV International Forum (GIF). The coolant of lead-based fast reactor can corrode metals. The existence of impurities in coolant will affect the safe operation of the lead-based reactor. Under this background, the application of impurity measurement in lead-bismuth alloy with laser-induced breakdown spectroscopy (LIBS) technique was studied. The effects of laser focusing position, laser energy and delay time on Ni elements spectral signal were studied. The optimal experimental parameters for measuring impurities in lead-bismuth alloy with LIBS device were obtained. At the same time, quantitative analysis of Ni element in lead-bismuth alloy was performed by employing LIBS technique in the present paper. The coefficients of determination gained by internal standard method is 0.967. The detection limit of mass content is 0.0287%. The results show that it is feasible to use the laser-induced breakdown spectroscopy technique to measure impurities in lead-bismuth alloy. LIBS technique has high application research value in the field of advanced nuclear energy.
Contrast of single-photon and two-photon absorption-induced charges in laser-simulated single event effects
Zhang Chenguang, An Heng, Wang Yi, Cao Zhou
2022, 51(9): 20210954. doi: 10.3788/IRLA20210954
[Abstract](126) [FullText HTML] (16) [PDF 1347KB](20)
By using the ways of theoretical derivation and simulation experiments, the quantitative relationship between charge collection ability in pulsed laser simulation experiments is studied when single-photon absorption and two-photon absorption are dominant respectively. The effects of different optical parameters on ionizing charge concentration are analyzed in simulation experiments, and specific parameters such as laser wavelength, pulse width, energy and beam spot are determined. According to the characteristics of single-photon linear absorption and two-photon nonlinear absorption of pulse laser in Si, the quantitative formula of the ratio of charge generated by single-photon and two-photon absorption is derived. Through the verification experiments of 1064 nm and 1200 nm laser, it is found that the response pulse and the amount of charge generated have a good linear relationship with the pulse laser energy or energy square, and the charge generated by single-photon absorption is significantly higher than that by two-photon absorption when single-photon absorption and two-photon absorption are dominant respectively. It is proved that the ratio of the charge generated by the two wavelengths is approximately equal to the calculated result. The results show that the amount of charge induced by the 1200 nm pulsed laser 1 nJ2 is equal to the amount of charge induced by the 1064 nm pulsed laser 0.039 nJ.
Influence of solid-gas coupling thermal effect caused by stray light from laser window on beam quality
Zhang Yueting, Tan Yi, Wang Jihong, Peng Qi, Yang Zhikun
2022, 51(9): 20210966. doi: 10.3788/IRLA20210966
[Abstract](104) [FullText HTML] (15) [PDF 2898KB](23)
To achieve the sealing requirement, the laser transmission inner channel will add the window with an inclined angle at the end of thin channel, but the temperature rise caused by reflected stray light of the window irradiating the pipe wall will also increase the gas thermal effects. Aiming at the problem of irradiating and heating the straight pipe by the reflected stray light of the sealing window, a coupling simulation model of structure field-gas density field-optical field in the straight pipe was established, analyzing the influence of materials, wall thickness and structural forms on wave front distortion of beam. The analysis results indicate that among three materials of equal quality, aluminum, copper and steel, the beam wave front distortion caused by the aluminum pipe is the smallest, which is only 50% of that of steel and copper; reducing the wall temperature and the beam distortion by adding heat dissipation fins or high thermal conductivity carbon film outside the pipe is not ideal and the wave front RMS value is reduced by no more than 3%; increasing the wall thickness and raising the pipe heat sink are the most effective solutions to reduce the beam distortion, the RMS value of the aluminum pipe outlet reduces from 36.1 nm to 21.4 nm and each order aberration is improved while the wall thickness increasing from 8 mm to 16 mm. The research results can provide a certain reference for the pipe design of inner channel and thermal effects evaluation.
Elevation control points extraction of spaceborne lasers with multi-feature parameter constraints
Mei Yongkang, Xie Junfeng, Chen Wei, Liu Ren
2022, 51(9): 20210997. doi: 10.3788/IRLA20210997
[Abstract](97) [FullText HTML] (18) [PDF 2929KB](21)
The point elevation accuracy of spaceborne laser is the basis of its auxiliary optical stereoscopic image composite surveying and mapping. This study proposes a method for extracting elevation control points of spaceborne lasers based on multi-feature parameters constraints in response to the requirements for the accuracy of laser elevation control points in optical image stereo mapping. This method utilizes the vertical structure information of the target objects contained in the full-waveform data to analyze the characteristics of the high-precision laser elevation control points, and realizes the constraint screening step-by-step based on the validity of data, the number of waveform peaks and echo characteristic parameters. The signal-to-noise ratio, kurtosis and skewness are selected as evaluation indexes. Through the calculation, statistics and analysis of the echo characteristic parameters, the thresholds are determined, and finally the valid waveform data that can be used for spaceborne laser elevation control points can be extracted efficiently. Taking the laser data of GF-7 as an example, such six typical feature samples as grassland, gobi, road, water body, sandy, and cultivated land are selected to determine the suitable thresholds of echo characteristic parameters for GF-7. Taking the airborne LiDAR point cloud data in Jiangsu area as a reference to verify and analyze the extraction accuracy, the experiment results show: based on the multi-feature parameters constraint algorithm, using the set parameter thresholds suitable for the GF-7, the valid waveform can be extracted from the original waveform data efficiently and accurately for the production of high-precision elevation control points. Taking the elevation difference of 0.32 m from the parameter data as the elevation accuracy requirement, the average extraction accuracy is 90.34%, and the average measurement accuracy of the extracted laser elevation is better than 0.5 m.
Optimization method of diffraction efficiency of liquid crystal spatial light modulator based on spline interpolation
Kang Ding, Wang Chunyang, Wang Zishuo, Wang Zeng, Zheng Qingquan
2022, 51(9): 20210827. doi: 10.3788/IRLA20210827
[Abstract](61) [FullText HTML] (21) [PDF 1956KB](25)
To reduce the diffraction efficiency of liquid crystal spatial light modulator, an optimization method of diffraction efficiency of liquid crystal spatial light modulator based on spline interpolation is proposed. According to Tyman-Green interference principle, the phase modulation system is built. Loading on the modulator with a grayscale map of step change, the phase modulation curve of liquid crystal spatial light modulator is drawn by calculating the movement of interference fringes. The cubic spline inverse interpolation method is used to correct the phase modulation curve and to realize the compensation of the phase modulation amount. The diffraction efficiency test system of liquid crystal spatial light modulator is set up, and the experimental verification of the proposed optimization method is carried out and compared with the stochastic gradient descent method. The results show that when the beam deflection angle is 1.56°, 0.78°, 0.39° and 0.19°, the diffraction efficiency of the proposed method can increase by 30% to 40%. Compared with the stochastic parallel gradient descent method, the diffraction efficiency increases by 2%-8%. This method can effectively suppress the gate lobe energy, improve the diffraction efficiency of the main lobe beam, and overcome the disadvantages of the stochastic parallel gradient descent method, such as a number of iterations, slow optimization speed, and easy to fall into local optimal.
Wavelength selection and detection performance of DIAL for formaldehyde gas detection
Xin Wenhui, Bi Yuanshuo, Li Shichun, Li Yaofei, Hua Dengxin
2022, 51(9): 20210925. doi: 10.3788/IRLA20210925
[Abstract](71) [FullText HTML] (12) [PDF 2523KB](23)
In order to detect formaldehyde gas in severe chemical pollution area, the research of concentration detection for formaldehyde by differential absorption lidar (DIAL) is carried out in this paper. Based on the principle of differential absorption lidar and the strong absorption of formaldehyde gas in the mid infrared band, the detection wavelengths of ${\lambda _{\rm on}}$ and${\lambda _{\rm off}}$for the formaldehyde are selected in consideration of the influence of atmospheric interference gas under open optical path. According to the concentration inversion method of differential absorption lidar and combined with the system parameters, the effects of the detection distance, gas concentration and interfering gas on the system perform are studied. The results show that the system can detect formaldehyde concentration in the range of 0.017-1.5 ppm (1 ppm=10−6) and within the distance of 0.4-1.1 km, and the relative error is less than 5%, which can meet its demand for formaldehyde detection in severe chemical pollution area. This paper can provide a theoretical and technical basis for the development of mid infrared differential absorption lidar system for monitoring the unorganized emission of formaldehyde in severe chemical pollution area.
Materials & Thin films
Development of the aluminum substrate reflective film in the off-axis three-mirror optical system
Zhang Pengquan, Chen Jiaqi, Shi Yijun
2022, 51(9): 20210900. doi: 10.3788/IRLA20210900
[Abstract](94) [FullText HTML] (12) [PDF 1234KB](33)
The off-axis three-mirror optical system has been widely adopted as the design scheme for spectral imaging system because of its wide service band, high image quality, controllable stray light and other advantages. In this paper, an optical system is designed using Code V. Based on the theory of polarization of light, the conversion relationship between film samples and the polarization fidelity and phase difference of the system is derived. After that, with aluminum substrate as the base material, and silver, alumina and titanium dioxide as coating materials, the reflective film is developed based on the basic theory of optical thin films, which features the incident angle of 38.5°, RS>99.96% and RP>99.8% in the range of 1 545-1 555 nm, and the phase delays of P-light and S-light smaller than 1°. Film design and simulation analysis are completed in the film design software. Using the high-performance optical coating machine designed by Leybold Optics, the aluminum substrate reflective film for the off-axis three-mirror optical system is prepared. S and P reflectance spectra and the phase of the coating samples are tested by Lamda1050 spectrometer. The results meet the design specifications. The research is of great significance in practice and engineering projects.