Research On Surface Damage And Internal Stress Of High-power Short-pulse Laser On Optical Components

Fused silica is widely used in high-power and intense laser systems due to its good optical properties and excellent chemical stability.At high power laser density,fused silica optical components are prone to damage due to complex physical and chemical mechanisms,laser damage will generate stress inside the fused silica optical element,and modulate the subsequent incident laser,resulting in uneven laser output,which may cause more cascading damage to the downstream optical components of the optical path.As a result,the performance of the high-power and intense laser device drops sharply.On the basis of traditional research on the temperature field of laser-induced optical components,this paper establishes a finite element model of laser-induced damage to fused silica optical components,and studies the characteristics of the damage morphology near the damage pit of fused silica optical components,the stress changes inside the optical material after laser-induced damage,and grasps the physical mechanism of laser damage.By comparing the initial damage morphology,temperature field and stress field distribution in the presence or absence of bubbles,the influence of internal bubble defects on the damage and its damage characteristics are analyzed.The specific research content is as follows:(1)Based on the theory of thermodynamic,this paper establishes a finite element numerical model of the interaction between millisecond pulsed laser and fused silica,and studies the initial damage morphology,internal temperature distribution and three-dimensional stress distribution inside the optical component after the material is cooled when the pulse is stopped.The results obtained are consistent with the three-dimensional stress measured by the experiment,which verifies the feasibility and accuracy of the model.This paper analyzes the formation mechanism of the surface damage of fused silica under millisecond laser irradiation,especially the internal residual stress.The radial and circumferential stress distributions at different depths inside the sample are obtained,and the influence of different pulsed laser energy on the stress field inside the sample is analyzed.The calculation results show that the radial compressive stress(negative value)near the damage pit will gradually transform into tensile stress(positive value)along the depth direction,and the circumferential stress along the radius will gradually transform from compressive stress to tensile stress.In addition,with the continuous increase of pulsed laser energy,the magnitude of radial and circumferential stress and its influence range have increased significantly.(2)Considering that bubble defects are prone to appear in the fused silica during the actual preparation process,by setting an air area inside the existing model,this paper establishes a fused silica model with bubble defect,and analyzes the influence of the presence or absence of bubble and the different positions of the bubble on the damage morphology,temperature field and stress field.The results show that the initial damage depth of the sample surface will increase when there is bubble,and there will be an extreme value of tensile stress around the bubble.Under the influence of bubble,the ability of fused silica to resist laser damage is reduced,and damage pit appears on the surface of the sample faster.At the same time,after increasing the incident laser energy,the tensile stress around the bubble of the sample will further increase,resulting in the fused silica being more prone to damage inside the fused silica under higher energy pulsed laser irradiation.In addition,as the position of the bubble continues to move downward,its influence on the internal stress of the sample,especially the stress around the bubble,is gradually weakened.The research results in this article will not only help to deepen the understanding of the damage process and damage mechanism of fused silica optical elements with or without bubbles under the action of millisecond pulsed lasers,and analyze the influence of internal bubble defects on the ability of fused silica to resist laser damage,but also provide theoretical references for improving the preparation and processing technology of fused silica optical elements and subsequent damage repair work.