Optical Coatings for High Average Power XeF Lasers: Final Report

摘要

Porous silica, calcium and magnesium fluorides were investigated for potential use as antireflective coatings for XeF lasers. Excellent optical properties were obtained for all types, and laser damage thresholds were in the range 18-25 Jcm sup 2 at 350 nm for 25 ns pulses at 25 Hz pulse repetition frequency. Studies of the effects of the XeF laser environment on these coatings were incomplete. Three oxides, ZrO sub 2 , HfO sub 2 , and Ta sub 2 O sub 5 were investigated as the high index components to be paired with low index porous SiO sub 2 for highly reflective dielectric coatings. Single oxide layers had indices in the 1.7-1.8 range and HfO sub 2 coatings had the highest damage threshold at about 5 Jcm sup 2 . An unexpected problem arose on attempts to prepare multilayer coatings. Stress in the coating after 6-8 layers had been put down, gave rise to crazing and peeling. This could not be avoided even on extending the curing process between coats. (ERA citation 13:036961)