<title>Stress and environmental shift characteristics of HfO2/SiO2 multilayer coatings</title>

Abstract

HfO<SUB>2</SUB>/SiO<SUB>2</SUB> polarizer coatings for 1054 nm have been produced that have low stress at explicit environmental conditions without the employment of backside stress- compensation films. In this process hafnia is condensed from a metallic melt and silica from an oxide source, both via electron-beam evaporation. Specifically, this process has been adopted for multilayer designs with stringent requirements on spectral control and wavefront distortion. Efforts to meet these requirements have prompted various investigations of coating stress and spectral behavior, especially under changing environmental conditions. Results have shown that coating stress and optical thickness vary significantly with humidity. THese quantities have been measured under both ambient air and dry nitrogen atmospheres. The effects of coating parameters on stress and environmental stability have been examined for an experimental hafnia/silica polarizer coating. The aforementioned parameters are hafnia deposition rate, oxygen pressure during hafnia deposition, and oxygen pressure during silica deposition. Results indicate a strong correlation of coating stress to oxygen pressure during the silica evaporation. Data on the aging of stress in hafnia/silica coatings will also be presented. The HfO<SUB>2</SUB>/SiO<SUB>2</SUB> process has ben utilized in high-laser-damage- threshold coatings for the OMEGA laser system and for National Ignition Facility development coatings at the Laboratory for Laser Energetics.