熔石英光学元件亚表面损伤紫外吸收钝化机制研究

The UV laser induced surface damage of fused silica optics at fluence far below the intrinsic damage threshold severely limits the laser operational fluence level and lifetime of optics. Recent studies suggest that two sources of sub-band absorption exist that are primarily responsible for laser induced surface damage of fused silica optics at the present operational fluence of UV laser. One is the photoactive impurity, and the other is a thin layer of electronically defective material associated with even minute fractures of subsurface damage inevitably produced during traditional grinding and polishing processing. In this work, we investigate the physical mechanism of reconstructure of defective material layer of subsurface damage that is not contaminated by photoactive impurities under advanced thermal annealing or laser annealing treatment to modulate the UV absorption of subsurface damage. By systematically studying the detailed parameters that influence the effect of UV absorption passivation for the defective layer on the subsurface cracks without modifying the main macroscopic morphology and shape of subsurface damage, the change principles of structure and light absorption properties of defective layer of subsurface cracks are explored, which is of importance for further understanding the action mechanism of subsurface defect on the laser induced damage. The study of this project can provide technical and theoretical supports for improving the laser damage resistance performance of subsurface damage and developing new and economic surface processing techniques for fused silica optics.

熔石英光学元件在远低于其本征损伤阈值的通量下的紫外激光诱导损伤问题严重限制了激光的运行通量水平和元件的使用寿命，最新的研究结果指出在目前的紫外激光器运行通量下导致熔石英元件表面产生激光诱导损伤主要有两大类亚禁带吸收性前驱体，一类是光敏杂质，另一类是传统研磨和抛光不可避免引入的亚表面损伤中的微裂纹表面存在的电子缺陷材料层。本项目针对无光敏杂质的亚表面损伤，研究微裂纹表面缺陷层在先进的热退火或激光退火作用下进行重构改变其紫外吸收特性的物理机制，通过系统研究在亚表面损伤宏观形貌基本不变的情况下缺陷材料从微观上进行重构钝化其紫外吸收性质的具体参数，探索亚表面微裂纹缺陷层结构和光吸收特性的变化规律，深入认识亚表面损伤在激光诱导损伤中所起的作用机制，为改善亚表面缺陷的抗激光损伤性能以及开发新型的元件表面加工技术提供科学依据和理论指导。

大口径熔石英光学元件的紫外激光诱导损伤问题严重限制了高功率固体激光装置的激光的运行通量水平和元件的使用寿命，熔石英亚表面紫外吸收性缺陷是在高通量紫外激光作用下引起熔石英元件表面损伤及其增长的根本因素。目前光学元件表面的激光诱导损伤仍然是限制高功率激光装置通量的瓶颈，抑制光学元件表面损伤及其增长以保证激光通量水平并延长元件使用寿命是大型高功率激光装置长期稳定运行需要解决的关键问题之一。本项目通过对熔石英光学元件亚表面损伤紫外吸收类缺陷的系统研究，发现激光损伤阈值与亚表面紫外吸收类缺陷的密度严格负相关，通过钝化亚带隙紫外吸收类缺陷减小其密度可以极大提升激光损伤阈值。本项目开发了方便快捷地利用CO2激光钝化乃至消除紫外吸收缺陷的方法，研制了基于假想温度调控的CO2激光熔石英元件损伤修复工艺，在我国最新型的神光系列高功率激光装置应用表明，研制的修复工艺可以有效抑制光学元件表面损伤及其增长，保证激光通量水平，并延长元件使用寿命，维持了大型高功率固体激光装置长期高效稳定运行。