Studies on subsurface damage detection and wet-etching process of K9 optics

Effects of wet-etching with four kinds of etching solution on the surface of K9 optical components were examined. By investigating the change pattern of wet-etching rate at different depth and surface parameters before and after corrosion, the depth of polishing redeposition layer was estimated. When etched to the depth of 600 nm, the loose polishing redeposition layer and the subsurface damage of the optics were mostly removed, hence the laser damage threshold was improved. However, with 1500 nm in etching depth, the subsurface flaws and cracks appeared which lowered the laser damage threshold of the optics. The result shows that certain solution etches K9 optics with controllable rate and the laser damage threshold of the optics is improved.