Direct comparison of laser-induced damage threshold testing protocols on dielectric mirrors: effect of nanosecond laser pulse shape at NIR and UV wavelengths

Abstract

As a rule of thumb, laser-induced damage threshold (LIDT) is often reported in terms of a single number, without even mentioning the testing details. However, meaning of reported LIDT numbers could be different depending on the testing protocol used. Such differences are not always obvious to practitioners that are designing or building laser systems (users of LIDT numbers). Furthermore, the properties of laser sources used for LIDT testing could also be very different among various testing laboratories. Thus, in order to exemplify possible effects of LIDT testing details on reported values an experimental study is conducted, where direct comparison of the most popular testing protocols, namely 1-on-1, S-on-1, R-on-1, and Raster Scan, is made. Experiments were organized in such a way that all the tests for the wavelength of interest were done on the same sample (conventional high-reflectivity HR mirror) by using both injection-seeded pulses (single longitudinal mode) as well as non-seeded (multimode) pulses with comparable effective pulse duration. Two sufficiently large dielectric mirrors were tested. Experiments were conducted for fundamental- (1064 nm) and third- (355 nm) harmonic wavelengths of Nd:YAG laser. The LIDTs obtained by using distinct testing protocols as well as pertinent damage morphologies are directly compared and discussed.