2022 Vol. 43, No. 2

2022, 43(2): 1-6.
Optical design and analysis of illumination system based on augmented reality
MA Linfeng, LIU Zhiying, HUANG Yunhan, ZHANG Yuhui, FU Yuegang
2022, 43(2): 179-190. doi: 10.5768/JAO202243.0201001
Illumination system is an important part of the augmented reality (AR) optical system, and its volume, illumination uniformity and energy utilization directly affect the quality of the AR system, so it is important for secondary light distribution of light source in illumination system. The free-form surface lens and illumination system of the AR system were studied, and the correspondence between light collecting angle and volume of collimating system was analyzed. Based on the detailed analysis of surface shape construction of collimating system, the surface shape of catadioptric collimating system reflected by the central transmission edge was solved. Combined with partial differential equation method and meshing method, a free-form lens was designed. The liquid crystal on silicon (LCoS) illumination system was composed of system and polarized beam splitter prism. After simulation analysis, the system illumination uniformity is 91.96%, and the optical efficiency is 66.6% without the effect of polarization. The system has simple and compact structure, small volume, light weight, and high illumination uniformity, which can meet the needs of AR glasses.
Design of optical system for high-precision laser ranging
LIU Yucheng, WANG Chunze, SONG Youjian, XIE Hongbo, YANG Lei
2022, 43(2): 191-197. doi: 10.5768/JAO202243.0201002
With the development of laser radar technology and the improvement of ranging accuracy requirements, the new requirements are put forward for the transmitting and receiving optical system, which should have the characteristics of adjustable beam, small measurement spot and high echo efficiency. An transceiver integrated optical system working in the optical communication band of 1 550 nm was designed. The transmitting and receiving modules share part of the optical paths to reduce the receiving blind area and facilitate the miniaturization of the structure. In order to solve the problem of echo energy difference caused by different measurement distances and different surface inclinations, the beam expansion components of the optical system were made into a continuously adjustable structure with the magnification of 2~3.5 times. The two sets of double gluing lenses were used for chromatic aberration correction to reduce the influence of spectral width on the system propagation distance. After design optimization, the laser divergence angle after system collimation is less than 0.3 mrad, and the diameter of the emergent light spot is continuously adjustable from 6.26 mm to 10.20 mm. For the measurement targets within 50 m, the diameter of the irradiation light spot is less than 20 mm, and the divergence angle as well as the light spot diameter meets the above requirements at different zoom positions.
Diffraction efficiency of digital micromirror device in projection system
GU Xiaoyan, WANG Chunyan, SUN Hao, WANG Zhiqiang, LIU Huan
2022, 43(2): 198-203. doi: 10.5768/JAO202243.0201003
The digital micromirror device (DMD) as spatial modulation component is often used in projection optical system, when the incident light is long wave infrared, the diffraction effect affects the energy distribution into the system. The effect of the light incident angle on diffraction effect was mainly discussed. As a blazed grating model, the DMD was used to study the diffraction effect produced in long wave infrared band. Firstly, from the angle of optical path difference, the diffraction effect when the main and counter diagonals were in the open state was analyzed, and the diffraction effect was related to the incident angle. Then, the DMD was used as a blazed grating model and the vector diffraction theory was used to calculate the diffraction efficiency of DMD in the open state at 7.7 μm~9.5 μm band. The results show that when TM polarized light irradiating at an angle of 44°, the first order diffraction reaches a blazed state, and the diffraction efficiency can reach to 70%.
Selection and optimization of mirror structure of off-axis two-mirror afocal system
SONG Honghong, LIU Ting, QIAN Junhong, LI Jiawen, ZHANG Rongzhu
2022, 43(2): 204-212. doi: 10.5768/JAO202243.0201004
According to the structural characteristics of aspheric off-axis two-mirror optical system, the imaging characteristics of the system were analyzed by using primary aberration theory. Based on the characteristics of different aspheric surfaces, the vector expression of system aberrations was derived. Using the Seidel coefficients, the primary wave aberration of systems were expanded and values of system aberration for different aspheric surface shapes were specifically calculated. After the evaluation index of the off-axis structure was determined, the imaging qualities of different surface shape combinations were compared. Then the optimal surface shape selection method was analyzed by quantitative comparison results. The results show that compared with other reflector combination methods, the spherical aberration, coma and astigmatism of the off-axis double paraboloid system are all 0, the wavefront RMS is much better than λ/14 (λ=0.587 6 μm), and the Strehl ratio is greater than 0.8. According to the calculation results, it not only has a stronger ability to suppress multiple primary aberrations, but also can effectively compress the volume of the system.
Arrangement of microlens and image restoration technology of photon integrated interferometric imaging system
YU Haibin, CHEN Beixi, PAN Zhifeng, REN Weifeng, ZHANG Honggang
2022, 43(2): 213-220. doi: 10.5768/JAO202243.0201005
The photon integrated interferometric imaging system is an emerging imaging technology with small size, light weight and low power consumption, and its resolution is not limited by the aperture size of a single lens. For the image restoration problem of photon integrated interferometric imaging system, the studies on the image restoration technology and optimal arrangement of microlens array were conducted. The image restoration technology of photon integrated interferometric imaging based on the compressed sensing and the optimal arrangement design method of microlens array based on the image residuals were proposed. Through the computer simulation, the optimal design of the microlens array in the limited space volume could be realized, and the quality of the image restoration was improved significantly. The simulation results show that the system root-mean-squared error (RMSE) was reduced by nearly 90% through the image reconstruction method based on the compressed sensing algorithm, and the peak signal to noise ratio (PSNR) as well as the quality of the image restoration was improved significantly. Based on the proposed algorithm, the influence of the microlens arrangement of the certain aperture on the imaging quality is quantitatively analyzed.
Design and preparation of cut-off filter for observation scope
PANG Menglin, ZHOU Shun, GUO Feng, HANG Liangyi, XIAO Xiangguo
2022, 43(2): 221-227. doi: 10.5768/JAO202243.0201006
Based on the requirements of glued eyepiece for the optical filter in the observation scope system, a cut-off filter for the optical system of the scope was designed, which eliminated the half-wave hole of the filter and compressed the passband ripple. The optical filter was prepared by electron beam thermal evaporation technology and its transmittance was tested. The average transmittance in the range of 400 nm~630 nm is 95.76%, and the average transmittance in the range of 655 nm~800 nm is 0.06%. The sample passes the salt spray test and the mechanical firmness test, and the preparation results meet the design requirements.
Probabilistically shaped optical transmission method based on cascaded ROADM
LI Linan, ZENG Junjie, PU Minglong, XIE Suofei, LIU Wei, ZHANG Lei, REN Junqiang, XIN Ning
2022, 43(2): 228-233. doi: 10.5768/JAO202243.0201007
Aiming at the probabilistically shaped dual-polarization 64-ary quadrature amplitude modulation in coherent optical transmission systems, the impact of bandwidth narrowing caused by cascaded reconfigurable optical add-drop multiplexer (ROADM) on bit-wise achievable information rate (BW AIR) was experimentally studied. The three probabilistically shaped distributed signals based on Maxwell-Boltzmann distribution were adopted by transmitter. The experimental device included the generation of probabilistically shaped symbol sequence, the variable bandwidth optical filters that simulated ROADM cascade narrowing the overall frequency response bandwidth, and the simplified detection as well as the BW AIR calculation. The results show that the impact of the bandwidth narrowing is similar for different constellation entropies, and for the given optical signal-to-noise ratio (OSNR), the constellation entropy which produces the maximum BW AIR depends on the extent of bandwidth narrowing caused by cascaded ROADM. Finally, the BW AIR can be maximized by choosing the appropriate probabilistically shaped constellation distribution.
Auxiliary alignment technology for aerial refueling based on real-time image processing
ZHANG Jianhua, GAO Shuaihua
2022, 43(2): 234-239. doi: 10.5768/JAO202243.0202001
Aiming at the difficult problem of refueling docking in aerial refueling flight test, an auxiliary alignment system for refueling docking section based on real-time image processing was designed. The accurate relative position between the fuel receiving head and the center of the refueling cone sleeve was calculated through image measurement technology, so as to realize the real-time synchronous display of position parameters and video images, which was used for the auxiliary alignment of air refueling docking. The key technologies involved in the system, such as cone tracking technology under complex optical conditions, camera calibration technology based on constraints and real-time measurement technology of relative position of oil feeding and receiving components were studied. The experimental results show that the algorithm can realize fast and stable recognition and tracking of cone images in complex air environment. Binocular vision forward intersection measurement was used to calculate the relative position between the refueling cone sleeve and the fuel receiving head in real time. Compared with the post-processing results, the accuracy is better than 0.1 m, which can assist the pilot in air refueling docking operation and improve the success rate of refueling and receiving docking.
FPGA-based real-time Bayer demosaicking algorithm and its implementation
ZHANG Zeyu, ZHANG Hong, WU Lingfan, YANG Yifan, LI Xuliang
2022, 43(2): 240-247. doi: 10.5768/JAO202243.0202002
The Bayer array is widely applied in the front-end sensors such as complementary metal oxide semiconductor/charge-coupled device (CMOS/CCD), in order to compress and encode the color images. The Bayer array is restored to red, green and blue color arrays by demosaicking algorithm, and the performance of the algorithm affects the imaging effective resolution and texture details. With the development of semiconductor technology and proposal of demand of new applications such as target recognition, the image devices move toward high resolution and low latency, and the original demosaicking algorithm encounters performance bottlenecks. A real-time demosaicking algorithm based on the field programmable gate array (FPGA) was proposed, which could accurately extract the local gradient direction of the image and guide the interpolation restoration of the color. The overall algorithm only needed 7 lines of data delay, and fully considered the hardware characteristics of FPGA, and designed the modules such as line buffer, gradient operator and gradient direction interpolation to reduce the hardware cost. The experimental results show that the algorithm can achieve the micron-level latency, and maintain the restoration effect of texture detail area of the image. The average peak signal to noise ratio (PSNR) on Kodak data set can reach to 38.26 dB.
Driving vehicle elements detection method based on optimized YOLOv4 algorithm
CHEN Yaozu, GU Yuhai, CHENG Xia, XU Xiaoli
2022, 43(2): 248-256. doi: 10.5768/JAO202243.0202003
The rapid increase in the number of vehicles also brings a series of management problems. The intelligent transportation system is an effective solution. Due to the traditional target recognition method was greatly affected by factors such as weather, distance, angle, and illumination, and the accuracy of the information detection of driver's face, hand which was based on the original YOLOv4 algorithm was not high, a detection and positioning method based on the optimized YOLOv4 algorithm was proposed. While adding a smaller detection scale to the original YOLOv4 network, a fuzzy ISODATA dynamic clustering algorithm was used to optimize the number of a priori frames, and the experiments using the real intersection data set were carried out. The experimental results show that the optimized network has an average accuracy of 98.56% between classes in the training set and a detection frame rate of 41.43, which are higher than those of the original network.
Fish stock detection algorithm based on zebrafish image features
GUO Guisong, LIN Bin, YANG Xia, ZHANG Xiaohu
2022, 43(2): 257-268. doi: 10.5768/JAO202243.0202004
The computer vision methods are increasingly applied to the study of zebrafish stock behavior. However, due to the large form changes and many occlusions in the swimming process of zebrafish, it is still a very challenging problem to accurately and robustly detect the zebrafish. To solve this problem, a fish stock detection algorithm based on zebrafish image features was proposed. Firstly, by analyzing the target characteristics, a detection method using fish head and fish tail instead of the whole fish was proposed, which solved the problem that the traditional whole fish detection failed in the case of fish stock cross occlusion. Then, the training set was automatically constructed based on zebrafish image features, which avoided the time-consuming and laborious problem of manual annotation in deep learning. Through the processing and verification of the actual zebrafish videos, and compared with the existing algorithms, the proposed method has better experimental effects in the performance indexes such as annotation rate, recall rate and occlusion detection rate (ODR). In terms of annotation performance, the total annotation rate of the proposed automatic annotation method is 87.40%. In terms of the effect of training set, the automatic annotation algorithm combined with manual correction reduces the annotation time by 93.11% compared with the manual annotation method, and the mean average precision (mAP) is 79.80%. In terms of target detection, when the target occlusion rate is 42.72%, the proposed detection algorithm can obtain the recall rate of 82.0% and the occlusion detection rate of 58.02%.
SLAM algorithm of dynamic environment based on semantic prior and geometric constraints
ZHANG Haocheng, WANG Xiaohua, WANG Wenjie
2022, 43(2): 269-277. doi: 10.5768/JAO202243.0202005
The feature points of moving objects in the actual environment are added to the calculation of camera pose, and the feature points in the static environment are over-sparse, which will lead to the low accuracy and poor robustness of the traditional visual simultaneous localization and mapping (SLAM) algorithm of mobile robot in pose estimation. A bilateral semantic segmentation algorithm based on branching hole convolution was designed to divide the environment into potential motion region and static region. Combined with geometric constraints to perform secondary judgments of static feature points and judgments of mobile feature points without prior dynamic markings, the dynamic feature points were removed from all the feature points uniformly extracted in advance, and only the static feature points were used to solve the camera pose and construct the static environment map. The experiment on the TUM common dataset shows that the positioning accuracy of SLAM in dynamic environment of the proposed algorithm is obviously better than that of other existing methods. The mapping experiment was carried out in the real environment with moving objects, and compared with the ORB-SLAM2 algorithm, the map constructed in the dynamic environment was clearer.
Fluorescence spectrometer based on SiPM single photon detector
ZHANG Fei, ZHAO Tianqi, CHEN Yi, ZHANG Xuecheng, JIN Shangzhong
2022, 43(2): 278-283. doi: 10.5768/JAO202243.0203001
In order to solve the main problems of the laser-induced fluorescence detection system, such as complex optical structure, large volume, high cost and insufficient sensitivity, a sensitive and miniaturized fluorescence spectrometer was proposed. The spectrometer used a 349 nm semiconductor laser as the excitation light source, adopted an orthogonal optical path, coupled a 4×4 narrowband filter array and a silicon photomultiplier (SiPM) array with single photon sensitivity, which could realize multi-channel detection of spectral information. It had the advantages of compact structure, low cost and good stability. Sodium fluorescein was used for performance evaluation of the spectrometer. The experimental results show that the detection limit of the spectrometer is better than 5×10−11 mol·L−1. The linear correlation coefficient of the fluorescence intensity is 0.998 39 with the concentration from 5×10−11 mol·L−1 to 1×10−9 mol·L−1. In addition, the spectrometer also has good repeatability, and the relative standard deviation of the fluorescence peak intensity is less than 10%. Therefore, the spectrometer has the advantages of high sensitivity, good linearity, strong repeatability and reliability, and can meet the needs of on-site real-time detection.
Stress measurement of transparent elements based on polarized camera
GAO Yang, WAN Xinjun, XIE Shuping
2022, 43(2): 284-290. doi: 10.5768/JAO202243.0203002
The stress measurement is of great significance for the manufacture and use of optical elements. Based on the principle of stress birefringence, a method to measure the stress distribution by polarized camera was proposed. The stress value and calculation formulas of stress direction were derived from Stokes matrix and Mueller matrix, and the main errors affecting the measurement accuracy of the system were analyzed theoretically. In order to verify the feasibility of the method, a device for measuring the stress distribution was constructed. A quarter wave plate of 633 nm was measured by this device, and the error was 0.86 nm. The full-field stress phase retardation and stress direction diagrams of headlight lens were obtained by further measurement. The measured phase retardation was used to calculate the stress birefringence value of central region of the lens of 9.21 nm/mm and the principal stress difference of 2.45 MPa. The symbolic rules were used to adjust the stress direction of the lens, and the results accorded with the principle of stress continuity. This method measures the stress distribution without rotating the optical elements, which can realize the real-time measurement of stress retardation and stress direction.
Calibration method of 3D scanner tilt angle based on IMU
XI Shaojie, ZHANG Zonghua, GAO Nan, MENG Zhaozong
2022, 43(2): 291-297. doi: 10.5768/JAO202243.0203003
The 3D scanner has been widely used in 3D scene reconstruction, intelligent manufacturing, automatic driving, virtual reality and other fields due to its advantages of high accuracy, fast speed, automatic processing and good stability. At present, most 3D scanners are installed on tripods, which is easy to cause an angle between the rotation axis of the scanner and gravity direction due to uneven ground. Therefore, the panorama and point cloud are skewed, which is a key problem affecting the accuracy of 3D reconstruction. To solve this problem, a method to calibrate the tilt angle of 3D scanner by using inertial measurement unit (IMU) was proposed. The proposed method used the acceleration information output by IMU to establish the connection between IMU and 3D scanner through an area array camera. The acceleration information of IMU was transferred to the central axis of scanner. Using the transferred information to calculate the angle between the rotation axis of scanner and gravity direction, then compensating this tilt angle to the generated panorama and point cloud, and the skew model can be corrected. Through experiments to compare the calculated angles before and after the calibration, the experimental results show that the tilt angle measurement error can be controlled within 0.5°. And after calibration, the accuracy is increased by at least 20%, which verifies the reliability and accuracy of the entire calibration method.
Differential confocal measurement method of linear scanning based on dual linear array camera
LAI Dongming, KONG Linghua, LIAN Guofu, YI Dingrong, ZHU Xingxing
2022, 43(2): 298-303. doi: 10.5768/JAO202243.0203004
Current microscopic 3D surface topography measurement technology has low detection efficiency and small measurement range. To address these problems, a linear scanning differential confocal 3D morphology measurement method based on dual linear array camera was proposed. The linear scanning light source and linear scanning stitching algorithm were adopted to synthesize pre-focus and post-focus images respectively. The differential image of the sample in the measurement area was obtained by using the differential algorithm. Combined with the pre-calibrated axial response curve, the 3D morphology of the sample was restored to achieve a large range of efficient measurement. The experimental results show that the measurement range and the measurement efficiency of the linear scanning differential confocal three-dimensional topography measurement method based on the dual line array camera are 16.48 times and 6.59 times of that of the white light interferometer respectively in the same time. Moreover, this method does not require to pause in the measurement process, and it can scan and detect the sample continuously and uninterruptedly only achieving one focus. The research results provide a basis to meet the requirements of on-line, real-time, efficient and large-range measurement in intelligent manufacturing.
Nonlinear errors correction based on trapezoidal plus sinusoidal phase shifting algorithm
ZHANG Guoming, HAO Zhidong, ZHAO Qi, ZHANG Zhiwen, CAI Bolin, LI Bing
2022, 43(2): 304-310. doi: 10.5768/JAO202243.0203005
The phase shifting profilometry (PSP) is a widely used optical three-dimensional measurement method. Its accuracy is affected not only by the phase unwrapping algorithm, but also by the nonlinearity of the projector and camera in the measurement system. Theoretically, the effect of nonlinear errors can be reduced by projecting more fringes, but definitely increases the measuring time. To improve the efficiency of errors correction, a measurement method based on trapezoidal plus sinusoidal phase shifting was proposed. This method required two groups of improved trapezoidal phase shifting fringes and only one sinusoidal fringe. The trapezoidal fringe provided the information of image intensity and fringe order. The image intensity information could be used to obtain the nonlinear response curve of the system and further eliminate the nonlinearity of the system. The sinusoidal fringe could obtain the additional fringe by Hilbert transform to calculate the truncated phase information, and the corrected truncated phase information could be used to obtain the three-dimensional information with higher precision. Compared with the previous trapezoidal plus sinusoidal errors correction method, the measurement efficiency of proposed method increased by 28%.
Spectral responsivity measurement technology for UV detector based on cryogenic radiometer
LI Yan, FAN Jihong, YU Bing, YUAN Lin'guang, SUN Yu'nan, QIN Yan, MA Li
2022, 43(2): 311-316. doi: 10.5768/JAO202243.0204001
By developing the vacuum multi-optical path switching component, the Y-type vacuum comparison channel and detector vacuum chamber were combined. A rapid switching of laser, ultraviolet continuous tunable monochromatic light and vacuum ultraviolet monochromatic light was realized with ultra-high vacuum environment guaranteed. Utilizing a cryogenic radiometer as the measurement datum and a UV-enhanced silicon trap detector as the transfer standard, the absolute spectral responsivity of UV detectors from 115 nm to 400 nm were measured. Experimental results show an absolute spectal responsivity measurement uncertainty of 0.8%~1.5% (k=2) from 115 nm to 230 nm, and 0.5%~1.0% (k=2) from 230 nm to 400 nm.
Influence of InAlAs concentration on In0.83Al0.17As/In0.83Ga0.17As infrared detector characteristics
YE Wei, DU Pengfei, XIAO Sheng, LI Mengfei
2022, 43(2): 317-324. doi: 10.5768/JAO202243.0204002
The performance of infrared detector is affected by the doping concentration of each layer of internal structure, and the doping concentration of multiplication layer will significantly change the performance of the device. In order to reduce the dark current and improve the performance of the device, the ternary compound In0.83Al0.17As was used as the multiplication layer material, and with the help of simulation software Silvaco, the effects of the doping concentration in the multiplication layer of In0.83Al0.17As/ In0.83Ga0.17As infrared detector on the electric field intensity, current characteristics and optical responsivity of the device were studied in detail. The results show that with the increase of doping concentration in the multiplication layer, the peak value of electric field intensity in the multiplication layer increases, and the dark current and optical responsivity of the device decreases respectively. It is further found that when the doping concentration in the multiplication layer is 2×1016 cm−3, the device obtains the optimal performance, the dark current density is 0.621 44 A/cm2, and when the wavelength is 1.5 μm, the optical responsivity and specific detectivity are 0.954 4 A/W and 1.947 5×109 cmHz1/2W−1, respectively.
Optical chopper applied for calibration of vacuum ultraviolet detector
LU Fei, ZHANG Boni, QIN Yan, HU Tieli, YU Bing, SUN Yu’nan, CAO Feng
2022, 43(2): 325-330. doi: 10.5768/JAO202243.0204003
In order to precisely calibrate the absolute spectral responsivity of detector from 115 nm~400 nm based on cryogenic radiometer, an optical chopper used in vacuum was developed. The optical chopper consisted of blade, rotation axis, servo motor, U-shaped photoelectric switch, cooling module, bracket and controlling circuit could be used to modulate the weak vacuum ultraviolet-ultraviolet (VUV-UV) radiation signal to the alternating radiation signal which the frequency was known in vacuum cryogenic environment, and measured by lock-in amplifier. The experimental results show that the stability of the optical chopper is ±0.05 Hz at the frequency of 80 Hz, which meets the requirements of absolute spectral responsivity calibration of detector at 115 nm~400 nm in the vacuum environment of 10−4 Pa.
Simulation modeling of infrared images of space targets in jitter state
LIU Peijin, LI Mingyang, ZHANG Licai
2022, 43(2): 331-338. doi: 10.5768/JAO202243.0204004
The space targets are susceptible to jitter by space junk collision and interference. Aiming at the problem of model construction of infrared images of space targets in jitter state, the main noise of space-based infrared imaging system was analyzed, and the effect of stray light was considered. Based on the combination of Creator and Vega software platform, a modeling method of infrared images of space targets with surface defects in jitter state was proposed. The infrared radiation characteristics of space targets were analyzed according to their basic characteristics, and the 3D modeling of space target defects was carried out in Creator. The temperature field of the 3D model was analyzed according to the infrared radiation characteristics of the target and background, and the infrared image model was obtained by combining the analysis results with Vega infrared module. The mathematical model of jitter image was determined and the jitter effect was applied to the simulation image, and then the stray light effect was applied to obtain the final simulation image. The experimental results show that the infrared images of space targets in jitter state generated by this method are highly similar to the experimental images, which can provide an effective simulation system for space target detection and situation awareness.
High precision measurement method of laser beam pointing stability
YAO Linhai, LU Peiguo, YANG Yong'an, LONG Jingyu, YANG Xiulin, BU Yinghua
2022, 43(2): 339-344. doi: 10.5768/JAO202243.0207001
The laser beam pointing stability is a key index in the application research of high energy laser. The measurement of laser beam pointing stability is an important part of the performance realization of high energy laser system. A high-precision laser beam pointing measurement device was constructed with a long-focal focusing mirror and a high-resolution charge coupled device (CCD) as the main components. The gray centroid method was used to locate the center of the laser spot, the center location of the ideal laser spot and the real laser spot was verified, and the error was less than 1 pixel. The CCD high frequency sampling was used to count the center displacement of the laser spot in unit time, so as to obtain the index of laser beam pointing stability. The accuracy of measurement examples can reach to 1.25 μrad. The proposed method is simple and feasible, and has high measurement accuracy, which is suitable for laser beam pointing measurement of various wavelengths and for measurement of other related parameters.
Evaluation method of continuous laser interference effect
WU Fengling, LI Yongtao
2022, 43(2): 345-351. doi: 10.5768/JAO202243.0207002
The improved image correlation computing method was adopted. On the basis of accurate registration of images before and after interference, the image correlation was computed in pixels, the interference threshold was determined according to the human eye recognition effect, the statistic value of image effective interference pixels was calculated, and the laser interference effect was quantitatively described. The experiments of multi-band laser interference imaging system were carried out, and the laser interference images under different interference power were collected to evaluate the interference effect. The results show that the proposed method can accurately identify the local changes of the images, objectively reflect the image quality changes, and give scientific evaluation results for the laser interference imaging images under different power in each band, and the processing speed of a single pair of images is better than the second level, which has certain engineering application value.
Experimental study on laser cleaning of paint layer on white marble surface
YANG Yiran, YU Lidong, ZHA Rongwei, LI Long, BAI Yang
2022, 43(2): 352-358. doi: 10.5768/JAO202243.0207003
In order to effectively remove the surface paint of the cultural relic of white marble, the area extrapolation method and laser-induced plasma spectroscopy (LIPS) method were used to obtain the ablation threshold power of the gold, silver paint layer and white marble surface. On the basis of this, the optimal laser power for removing paint without damaging the white marble substrate was determined. The image processing method was used to study the cleaning degree and variation trend of cleaning rate of the gold and silver paint on the surface of 10 mm×10 mm white marble by laser cleaning, and the optimal laser spot overlap rate and the optimal cleaning times were obtained. Finally, the image processing method was used to evaluate the cleaning effect of laser cleaning of paint layer on the white marble surface. More than 93% of the cleaning degree shows that the synergistic use of the area extrapolation method, LIPS method and image processing method can effectively improve the laser cleaning efficiency of the paint layer on white marble surface.