Laser-induced damage of optical thin films submitted to 343, 515, and 1030 nm multiple subpicosecond pulses

Optical materials submitted to multiple subpicosecond irradiations are known to exhibit a decrease of the laser-induced damage threshold (LIDT) with the applied number of pulses, an effect referred to as "fatigue" or "incubation." In this work, we experimentally investigate this effect for the case of optical thin films submitted to multiple exposures with 500 fs pulses at different wavelengths: 1030, 515, and 343 nm. Niobia, hafnia, and silica films made with dense coating techniques (magnetron sputtering, ion-assisted deposition, and reactive low voltage ion plating) are studied, as well as the surface of a fused silica substrate. These samples have been exposed to different pulse numbers (from 1 to 100,000) at a low-frequency repetition rate (less than 1 kHz) and the LIDT has been measured. The results reveal the differences between materials and for the various wavelengths such as the decrease rate of the LIDT or the stabilization level that is reached after multiple exposures. All the results evidence the role of native-and laser-induced defects that we discuss on the basis of published works on the subject. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)