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

Abstract

We study Laser-Induced Contamination (LIC) as a potential cause of optical losses and Laser-Induced Damage (LID) 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 515nm operated in ambient air. Based on the development of an experimental set-up for real time 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.

Laser-induced contamination deposit growth mechanisms on space optics

“…22 In consequence, we can say that the light-substrate interaction is the most important mechanism driving the first stage of LIC deposit growth and that the mechanism seems to have a thermal component even for the first growth stage where the deposit is only weakly absorbing. This model is also compatible with the observation of different c 1 values for different high reflective thin film stacks 8 differing at least by the fabrication method used (one electron beam deposited and the other IBS) and possibly by the high index material. Any of these differences may cause slightly different absorption of the mirrors.…”

“…The growth rate of LIC deposits as function of laser fluence in otherwise stable experimental conditions has been reported to be described by a simple proportionality law, 5 , 8 r=c1 F, with the proportionality factor c1 depending on the irradiated optical component (shortly called “substrate” in the following) 8 . The same proportionality law was also observed in UV light-induced CVD, where the substrate is heated in addition to the laser irradiation.…”

“…(a) Using the proportionality model as in Refs. 5 and 8. The proportionality between fluence and growth rate does not hold for toluene contamination on a silica-coated substrate that is described by three-photon absorption.…”

“…The usage of high power lasers in contaminated vacuum or sealed environments often leads to deposits that absorb a part of the light and may cause important problems as reduced laser output power 1 or laser-induced damage after many laser pulses 2 , 3 . This effect, 4 often short-hand named laser-induced (molecular) contamination (LIC), 5 , 6 is mostly known not only from satellites carrying laser-based instruments 1 , 7 but also from sealed lasers 4 and high repetition rate lasers in the visible or the ultraviolet (UV) 8 , 9 …”

“…2,3 This effect, 4 often short-hand named laser-induced (molecular) contamination (LIC), 5,6 is mostly known not only from satellites carrying laser-based instruments 1,7 but also from sealed lasers 4 and high repetition rate lasers in the visible or the ultraviolet (UV). 8,9 The LIC deposit formation mechanism has been studied for 1064-nm irradiation in a sealed environment and was modeled as interaction between laser light-and surface-adsorbed contamination molecules. 4 In satellites, the molecular contamination, which is at the origin of the absorbing deposits, is provided by polymers that are used in adhesives, electrical insulation of cables, vibration dampers, and many more.…”