Critical issues on the assesment of laser induced damage thresholds of fluoride multilayer coatings at 193nm

Optimization of deposition technologies improves the laser resistivity of fluoride multilayer coatings at wavelengths as short as 193nm Nevertheless, some problems of practical interest seem to be still unanswered: 1. Experimental data suggest, that these improvements of the LIDT of the coatings might be only temporal effects with a pronounced dependence on the storage time after deposition. 2. Can the LIDT of a long time stored sample become recreated to its as -deposited value by a conditioning process? 3. While 1-on-1 - LIDT indicates improvements, what happens when the coatings are stressed under multi pulse irradiation?. Investigations on the aging and the conditioning of fluoride multilayer coating were performed to give some detailed insights. Additionally, results of multi pulse LIDT experiments at 193nm on MgF2/LaF3 and AlF3/LaF3 dielectric mirrors are presented showing a remarkable decrease in LIDT with increasing pulse number.