Study of the picosecond laser damage in HfO2/SiO2 -based thin-film coatings in vacuum

The laser-damage thresholds of various HfO2/SiO2 based thin-film coatings, including multilayer dielectric (MLD) gratings and high reflectors of different designs, prepared by e-beam and plasma-ion-assisted deposition (PIAD) methods were investigated in vacuum and after air/vacuum cycling. Single- and multiple-pulse damage thresholds and their pulse-length scaling in the range of 0.6 to 100 ps were measured using a vacuum damage test station operated at 1053 nm. The e-beam-deposited high reflectors showed higher damage thresholds with square-root pulse-length scaling, as compared to PIAD coatings, which typically show slower power scaling. The former coatings did not appear to be affected by air/vacuum cycling, contrary to PIAD mirrors and MLD gratings. The relation between 1-on-1 and N-on-1 damage thresholds was found to be dependent on coating design and deposition methods.