激光诱导损伤是导致熔石英真空光学元件突发破裂的根本原因。本工作采用神光-Ⅲ原型装置终端光学组件的熔石英真空光学元件制作了标准样品, 统计分析了熔石英玻璃样品表面损伤形貌特征, 探究了激光诱导损伤对熔石英玻璃样品弯曲强度的影响。结果表明: 激光诱导熔石英玻璃损伤点形貌为典型的半椭球体, 损伤点深度随其长度增大呈上升趋势, 深度极限基本不超过2 mm; 损伤点对熔石英玻璃弯曲强度影响非常明显, 含损伤点的样品平均弯曲强度仅为不含损伤点样品平均弯曲强度的41%。随着损伤点长度和深度增大, 熔石英玻璃的弯曲强度总体呈下降趋势, 但当损伤点长度大于15 mm, 弯曲强度下降趋势明显缓和, 损伤点长深比对弯曲强度无明显影响。熔石英玻璃真空窗口光学元件安全设计, 应考虑玻璃弯曲强度离散性及持久应力作用综合影响, 且在损伤点位置处的最大弯曲拉应力不应超过其弯曲强度设计值。

Laser-induced damage is the fundamental cause of sudden rupture of fused silica vacuum optical elements. To investigate this damage on bending strength weakening to find safety design method, standard samples were made with fused silica vacuum optical elements in the final optics assembly of the SG-III prototype laser facility. The surface damage morphological characteristics of fused silica glass samples were statistically analyzed, and the influence of laser-induced damage on bending strength of fused silica glass samples was investigated. The results show that the damage morphology of laser-induced fused silica glass is typically semi-ellipsoid, the depth of the damage point increases with its length which is no more than 2 mm; The damage point has obvious influence on the bending strength of fused silica glass, whose average bending strength with damage point is only 0.41 times that of the samples without damage point. With increase of the length and depth of the damage point, the bending strength of the samples generally decrease. But when the length of the damage point exceeding 15 mm, its bending strength downward trend is significantly moderated, the ratio of length to depth of the damage point has no obvious effect on the bending strength. These data suggest that designing safe optical elements of fused silica glass vacuum window should comprehensively take into account dispersion of glass bending strength, persistent effect of the stress, and the maximum bending tensile stress distributed near the damage point should not exceed the design value of bending strength.