Study on correlation between the stray light protection functional film thickness and irradiation damage

Contamination in high-energy laser systems by stray light irradiating on 6061 aluminum alloy components is one of the common problems that hinder the operation of inertial fusion systems. We proposed a functional film based on anodization to improve light absorptivity and damage threshold. And obtained the effects of the oxide layer thickness on the optical properties and fundamental frequency laser damage of the films are experimentally studied. On this basis, the optical–thermal–mechanical coupling simulation of the film optical properties and the irradiation damage process is carried out using finite-difference time-domain and impurity doping finite element methods. This study have shown that functional thin film can effectively suppress the reflection of fundamental frequency stray light and the damage mechanism changes from explosive brittle splashing to melting/ablation with the increase in functional film thickness. The critical thickness depends on the incident laser parameters. For single-pulse irradiation with radius of 375 μm and the energy density of 0.5–1.0 J/cm², the critical thickness is 9–20 μm.