Cleaning Methods for Multilayer Dielectric Pulse Compression Gratings

Two cleaning methods for multilayer dielectric pulse compression gratings (MDG) were studied. The first method is SPM (Sulfuric-Peroxide Mixtures, 98wt%H2SO4+30wt%H2O2) + megasonic, and the second method is Oxygen plasma + HPM (Hydrochloric/Peroxide Mixture, 37wt%HCl+30wt%H2O2+DIH2O) + megasonic. To compare the cleaning effectiveness, the element content of sample surface, diffraction efficiency, surface roughness, temperature rising and laser damage induced threshold (LIDT) were measured. The 1-on-1 LIDT of samples cleaned by the first and the second methods are 7.55 and 5.32 J/cm(2) respectively, with 1064 nm laser pulse (12 ns, s-polarized) at incidence angle of 70 degrees. In addition, the sample cleaned by the second method has lower surface contamination content, but the sample cleaned by the first method has better performance in diffraction efficiency, surface roughness and temperature rising. By further analyzing, we find that element Fe brought by oxygen plasma cleaning process in the second method is the factor that affects the damage performance and temperature rising. Therefore, the cleaning method based on the first one, the SPM + megasonic is better for improving the laser damage performance of MDG.