Effect of ion beam figuring and subsequent antireflective coating deposition on the surface absorption of CaF 2 at 193  nm

The surface absorption of CaF at 193 nm after surface treatment by ion beam figuring (IBF) and the subsequent antireflective (AR) coating process was investigated by using the laser-induced deflection technique. In comparison to a standard pitch polishing, enhanced surface absorption (subsurface damage) is observed after IBF treatment. However, after AR coating deposition, the total surface absorption of IBF treated samples does not exceed values obtained for pitch polished samples. The experimental results provide indication that IBF treatment yields both fluorine displacement and deficiency in the CaF subsurface region, which is annealed during the coating process by the high temperature and the fluorine supply from the fluoride coating materials, respectively.