Optical Component Damage Threshold Test System Based On Machine Vision

Optical element is an important part of high-power laser device.The damage of optical element under high-power laser irradiation is the key to improve the load capacity and reduce the operating cost of high-power laser device.Therefore,the damage threshold and damage growth threshold are important indicators to evaluate optical elements.In this paper,machine vision technology is applied to the damage test of optical elements under high-power laser irradiation.Focusing on the target of accurately obtaining the energy density distribution of target surface,the damage test of optical elements under high-power laser irradiation and the calculation method of target surface energy density based on machine vision are carried out,and the damage data analysis software is developed,The surface damage of DKDP crystal and the surface damage growth of fused silica were verified.The research content includes the following four aspects:1.Design and construction of optical component damage test platform based on machine vision.An on-line beam quality acquisition and damage imaging system is built to realize the real-time monitoring,damage judgment and image acquisition of the beam quality,spot position and damage condition of the laser beam.An optical system with the functions of wavelength separation,beam combination,energy adjustment,beam splitting and focusing is built.2.Research on target energy density method based on machine vision.Aiming at the test error caused by the average energy density ratio in the traditional laser damage test and analysis method,the error minimization analysis and the energy density calculation method based on image processing are studied.According to the instability of the spot area and the uneven distribution of laser energy on the target surface,the image processing method for calculating the energy density of the target surface is studied.The results show that the energy density of each wavelength at each point of the target surface can be accurately obtained by using the image processing method,and the overlap of the spots among the wavelengths can be accurately judged,The energy density corresponding to the initial damage point and the total pulse energy of irradiation in the damage pit can be given accurately.3.Research on target surface energy density algorithm and damage data analysis based on machine vision.In order to accurately match the beam energy distribution with the location of the damage point,a laser spot center detection algorithm with improved threshold segmentation is proposed.The algorithm builds a threshold segmentation function by comparing the correlation coefficient between the light intensity value and the gray value,combining the laser spot energy distribution model and the effective area;finally,according to the laser spot contour shape,the center point is obtained by fitting based on the least squares method.Experimental results show that the IOU and LY values of this algorithm are 0.85 and0.14,respectively,which are better than the traditional adaptive threshold segmentation algorithms compared.The damage data analysis software was developed and the function test was completed.4.Application verification of optical component damage test based on machine vision.The experimental study on the initial damage law of the front and rear surface of DKDP crystal and the damage growth law of fused quartz optical element under 3? and 1? irradiation and double wavelength irradiation were compared.The results show that the target energy density processing method based on image processing can improve the accuracy of the damage growth threshold test results of small aperture non-uniform light spot,and effectively reduce the aperture effect in the damage threshold measurement,compared with the traditional method which uses the ratio of pulse energy to target spot area to determine the target energy density,It can solve the problem of energy density instability in the irradiation region caused by the incomplete overlap between the spot and the pulse under dual wavelength irradiation at the same time.