Parametric analysis of damage probability: a tool to identify weak layers within multilayer coatings.

The role of defects, inherent to fused silica substrate due to polishing and deposition processes, is interpreted in terms of laser-induced damage probability. Changes of damage threshold behavior are observed in bare substrate, monolayer, and multilayer coatings after irradiation with UV (355 nm) nanosecond laser pulses at different angles of incidence (0° and 45°) and polarizations (s and p). Statistical damage probability models are constructed for experimental data approximation. Effects of light intensification by standing waves within multilayer coatings and localization of the defects (surface, interface, and bulk) are considered as key factors within this work. Polishing defects are shown to be the limiting factor in the case of uncoated fused silica sample, as well as SiO₂ and HfO₂ monolayer coated substrates. The obtained results also suggest that damage threshold of almost identical sublayers constituting highly reflective multilayer HfO₂/SiO₂ coating with central 355 nm wavelength is a function of sublayer depth.