1077-nm, CW mirror thin film damage competition

Abstract

This year’s competition proposed to survey the damage resistance of near-IR high reflectors designed for continuous-wave (CW) laser applications. The requirements for the coatings were a minimum reflection of 99.5% at normal incidence for 1077-nm light. The participants in this effort selected the coating materials, coating design, and deposition method. Samples were damage tested at a single testing facility using a kW fiber laser source capable of delivering up to 10 MW/cm2 peak irradiance on target. A double blind test assured sample and submitter anonymity. The damage performance results, sample rankings, details of the deposition processes, coating materials and substrate cleaning methods are shared. We found that multilayer coatings using tantala or hafnia as high index materials were top performers under CW laser exposure within several coating deposition groups. Namely, dense coatings by ion-beam sputtering (IBS), plasma-enhanced atomic layer deposition (PEALD) and magnetron sputtering (MS) exhibited the lowest absorption & temperature rise upon CW laser irradiation without damage onset up to the maximum power density level available in this study.