Pulse-length scaling of laser damage at 249 nm in oxide and fluoride multilayer coatings

We have measured laser damage thresholds of a variety of fluoride-based multilayer coatings at 249 nm by using pulse lengths between 450 fs and 25 ns. Rare-earth fluoride materials yield coatings with damage resistance approximately three times greater than conventional oxide multilayers. In the scaling law, where the damage threshold is proportional to the nth power of the pulse length, the value of n changed between 1 and 0.25 over the range of pulse lengths employed.