Study On Damage Characteristics Of Optical Glass Induced By Combined Pulsed Laser

In high-energy laser systems,the anti-laser damage performance of optical glass limits the life of the entire equipment and even restricts the development of the entire system.At present,short-pulse lasers are mostly used in the research of laser damage of optical materials.In this paper,the mechanism and characteristics of K9 glass damage caused by combined pulsed lasers are studied from both experimental and numerical simulations,and the acoustic emission characteristics during the damage process are analyzed.In this paper,a combined pulsed laser(CPL,composed of millisecond laser and nanosecond laser separated by a certain time)experimental platform was built to study the effects of millisecond laser energy density and delay time on the damage characteristics and acoustic signals of K9 glass.The results show that the front surface is dominated by fusion damage,and the damage morphology can be divided into three types: ablation damage,fusion damage and cone damage;the back surface is mainly stress damage,and the damage morphology can be divided into small ones on the order of hundreds of microns.Size damage and large size damage on the order of centimeters.The laser damage process on the front surface is accompanied by strong acoustic emission,and its frequency spectrum is mainly distributed in the frequency range of 0-10 k Hz.Both the front and rear surfaces have the best time delay area,the corresponding damage probability and damage size are the largest,and when the time delay is the same,the sound signal attenuation duration of different laser energy densities is similar,indicating the same laser action process.As the energy density increases,the probability of damage on the front surface increases,and the probability of large damage on the back surface increases.At the same time,the damage size of the front and rear surfaces increases with the increase of the energy density.Compared with a single millisecond laser,the combined pulsed laser significantly improves the damage probability and damage size of the material.In addition,through the attenuation duration of the waveform oscillation and the sudden change of the acoustic signal,the degree of interaction between the laser and the material and the time of damage can be determined respectively.The temperature field and stress field distribution around the cone pit after the laser irradiation is calculated numerically.The calculation results show that hoop stress and radial stress are the main causes of stress damage to K9 glass.The stress damage at the surface of the molten deposit is mainly caused by compressive stress,and the surrounding area of the deposit is mainly tensile stress.The increase of the thickness of the molten deposits around the pits and the size of the conical pits will cause the stress to increase,which is consistent with the experimental results.This study is helpful to grasp the damage mechanism and physical laws of laser-induced component damage,and provides a certain reference for the research on the damage mechanism and damage process of single millisecond laser and CPL interacting with optical glass.