Analysis of laser-induced contamination at 515 nm in the sub-ps/MHz regime

We study laser-induced contamination (LIC) as a potential cause of optical losses and laser-induced damage of optical components for ultrashort pulse lasers with high average power in the MHz regime. Our work is conducted on dichroic mirrors designed for maximum reflection at 515 nm operated in ambient air. Based on the development of an experimental set-up for realtime monitoring of LIC and accelerated test protocols, we have conducted a parametric study on LIC development and studied its growth dynamics and morphology. We show that LIC is a main limitation of short-wavelength, high average power fs/ps lasers, with the formation of nanometric highly absorbing layers of carbonate compounds on the laser footprint, with evidence of thermal effects. It is also found that the last layer of the stack, at the interface between air and coating stack, is critical in the LIC growth which can open some perspectives for limitation of this effect. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)