In the running of ICF facilities, Sol-gel anti-reflective SiO₂ film of UV optics, for instance Grating Debris Shield (GDS), would inevitably get contaminated with tritium. These contaminated films need to be removed during the recycling of the hosting optics. The conventional wet ultrasonic cleaning method, however, would produce tons of tritiated water, which compared with gaseous or solid-state tritide, is much more toxic and difficult to dispose. In this work, we proposed a dry film removal method based on ion beam etching. The tritide is bombarded away along with SiO₂ film in form of volatile or solid-state particles. The volatile and solid tritide can be collected through filtration of tail gas and periodic cleaning of the chamber, respectively. Ion beam parameters are theoretically and experimentally optimized obtain a selective and gentle etching. The weakly bonded coating is etched much faster than the fused silica substrate, which ensures the selective etching of coating over the fine optics. Experiments on different off-line samples as well as the actual recycled optics from high power laser system show that this method is very effective. We also investigate the possible effects this method having on the optics performances, and no degradations are observed. Surface roughness and surface shape barely change after treatment. Laser damage resistance even increases slightly, probably due to the removal of redeposition layer introduced during polishing process.
 

Sol-gel,SiO2 film,dry removal,ion beam etching