Effect of high-temperature ablation on protective coating of ZnS optical windows

While infrared (IR) hard protective film of ZnS optical window is used in high temperature environment, its optical and mechanical stabilities are the premise of the IR optical system. IR hard protective film is deposited on ZnS optical windows by chemical vapor deposition (CVD), and ablation experiments are done to the maximum temperature the film can endure. The effects of ablation temperature on the optical and mechanical properties of the protective films are investigated by surface profiler, Fourier-transform infrared (FTIR) spectrometry, IR ellipsometer, and Metallographic microscope. It is shown that the optical and mechanical properties of ZnS hard protective film change little before 500°C, and film refractive index and optical thickness reduce while ablation temperature surpassing 500°C, forming crater-like ablation structure, which leads to the reduction of film combination signif icantly. © 2013 Chinese Optics Letters.