裂纹或气泡对熔石英损伤修复坑场调制的近场模拟

建立了含有裂纹或气泡的高斯型修复坑的3维模型, 用3维时域有限差分方法研究了熔石英后表面该类缺陷对355 nm入射激光的近场调制. 研究表明, 裂纹的调制明显大于气泡或者高斯坑本身, 因此为了抑制修复元件的初始损伤, 应尽量避免任何未修复的裂纹存在, 尤其是与入射光呈夹角约25°的裂纹, 同时应避免尺寸大于5 λ 的气泡存在. 当裂纹或气泡位于近表面层3 λ 以内且靠近修复坑环边缘时, 对场的调制最明显. 随着侧移的增加, 近表面区缺陷诱导场叠加, 强点总数涨落较大且易形成极大峰值, 特别是含有裂纹的情形; 远表面区强点总数逐渐增大并趋于稳定. 随着嵌深的增加, 强点的数目大体呈减弱趋势, 当嵌深大于3 λ 时, 逐渐趋于平缓振荡. 如果裂纹或气泡位于坑点正下方几个波长内, 激光辐照下其效果相当于延长了高斯坑的深度.

Near-field modulated simulation of repaired site contained crack or bubble in fused silica subsurface

Three-dimensional(3D) model of Gaussian repaired site contained crack or bubble is establishd,and 3D finite-difference timedomain method is used to simulate near-field modulation of 355 nm laser incidence by those defects on fused silica rear-surface.The results show that we should avoid any unrepaired cracks,especially cracks with incident angle of 65°,and the size of bubbles should be less than 5 A.All of the above can contribute to the weakening of the modulation around repaired pit.When crack or bubble distributes in the near-surface area(< 3λ) and close to the edge of pit ring,the field modulation is obvious.With the increasing of lateral gap, there will be a maximum due to electric field fluctuations near the surface area,especially when cracks are contained.And the electric field gradually stabilized when lateral gap is far from the surface.As the vertical gap increases,the number of large electric field grid points decreases,and stabilized oscillation emerges when vertical gap is larger than 3 A.If cracks or bubbles are located below Gauss repaired sites within a few wavelengths,its depth seems to be enlarged under irradiation.