Thickness dependence of damage thresholds for 193 nm dielectric mirrors by predamage sensitive photothermal technique

HR layer stacks with increasing number of HL pairs of fluoride materials deposited on different substrates have been successfully investigated with respect to the laser radiation damage threshold at 248 nm and 193 nm. In this paper the investigation has been extended on resonant as well as nonresonant oxide coatings deposited by ion beam sputtering (IBS). Compared to conventional evaporation and plasma ion assisted evaporation technique, IBS coatings exhibit a higher packing density, thus preventing water to enter the film which would degrade the quality of the coatings. In contrast, the thermal stress is increased in IBS layer stacks. The measurements were carried out by use of the pulsed thermal lens technique enabling us to measure the advent of optical breakdown induced by laser fluences in the subdamage range.