熔石英亚表面三维Hertz锥形划痕附近光强分布的数值模拟

Numerical simulation of light intensity distribution in the vicinity of three-dimensional Hertzian conical scratch on fused silica subsurface

熔石英亚表面划痕对入射激光的调制是导致光学材料损伤的主要因素.本文建立了熔石英后表面上三维Hertz锥形划痕模型,采用三维时域有限差分方法对划痕周围的电场强度进行了计算模拟,并分别讨论了划痕的深度、半径以及倾斜角度对入射光场调制作用的影响.结果表明:Hertz锥形划痕中心区域的电场增强效果最明显,最容易被辐照损伤;划痕的深度从λ变化到9.5λ的过程中,熔石英内的最大电场强度逐渐增大;半径小于1.5λ的Hertz锥形划痕较容易引起熔石英的损伤,当半径大于1.75λ时,熔石英内的最大电场强度都维持在2.5V/m,不再受半径大小影响;当入射激光在划痕的内侧界面和熔石英后表面之间发生内全反射时,光场增强效果愈加明显.

The main factor of laser induced damage is the modulation caused by the scratch in the subsurface of the fused silica.The three-dimensional Hertzian conical scratch（HCS） model on the exit surface is establised in this article.Three-dimensional finite-difference time-domain method is used to calculate and simulate the electric field intensity distribution in the vicinity of HCS.The effects of depth,radius and gradient angle of the HCS on incident light field modulation are analyzed,respectively.The results show that the electric field enhancement in the center of HCS is the largest.This area is apt to be damaged.The maximal electric field intensity in the fused silica will be enhanced as the depth of the HCS changes from λ to 19λ/2.The fused silica is liable to be damaged while the radius of HCS is below 1.5λ.When the radius is larger than 1.75λ,the maximal electric fields in the fused silica tend to be 2.5 V/m.And the maximal electric fields are independent on the radius.The effect of light intensity enhancement is more obviously when total internal reflection occurs between internal interface of HCS and the rear surface of fused silica.