Femtosecond 1030-nm mirror thin film damage competition

This year’s laser damage competition involves short pulse laser damage on high reflectors tuned for near normal incidence and >99.5% reflectance for 1030 nm. All laser damage testing was done by Lidaris Ltd. via a near Gaussian laser beam from a commercial laser system (Yb:KGW, Kerr lens mode-lock) operating at 500 kHz repetition rate with 200-fs pulse duration (FWHM). All testing was done in a similar fashion to the ISO 21254-1 and 21254-2 S-on-1 standards, yielding data on laser damage for 10x number of shots, where x = 0, 1, 2, 3, 4, 5, 6. Laser-matter interaction either leads to material removal and ablation or a more subtle coating admittance change. The former is referred to as catastrophic damage while the latter is referred to as color change. The choice of coating materials, design, and deposition method were left to the participants. A double-blind test assured sample and submitter anonymity. The damage performance results (LIDT), sample rankings, details of the deposition processes, coating materials and substrate cleaning methods are shared. These results are compared both to the nanosecond 1053-nm laser damage testing on high reflectors from the 2018 competition as well as the nanosecond-femtosecond damage testing study from the 2020-2021 years. All samples exhibited a fatiguing effect in the laser damage performance at high number of shots, but this was particularly noticeable for the color change damage type. We found that ion beam sputtered HfO₂/SiO₂ multilayer coatings of approximately 30 total layers did the best for the short pulse regime. This is in sharp contrast to the 1053-nm nanosecond study, which has demonstrated that electron beam deposited HfO₂/SiO₂ high reflectors are the clear winners.