Nanosecond 2053nm mirror thin film damage competition

We report the results of the 18th thin-film laser damage competition associated with the SPIE Laser Damage conference, organized to benchmark high-reflector (HR) multilayer dielectric mirrors for operation at 2053 nm — an increasingly important regime for thulium/holmium laser systems, but one with comparatively limited community laser damage performance data. Participants supplied 2-inch diameter HR mirrors specified for >99.5% reflectance at 2053 nm. In total, 49 samples were submitted by 26 organizations across eight countries; due to schedule constraints, 29 samples were tested under blind, anonymized conditions. Damage testing was performed in air at near-normal incidence using a longitudinally diode-pumped Tm:Ho:YLF source delivering 2053 nm pulses of 9.6 ns FWHM at 100 Hz, with a near-Gaussian spatial profile. A typical raster protocol was used to probe both stable damage initiation and catastrophic (propagating) damage; prompt “plasma” events without observable surface modification were also recorded as a separate category. Across the cohort, thresholds span more than an order of magnitude, underscoring the continuing sensitivity of nanosecond LIDT to design, materials, deposition method, and defect populations. Seven samples exhibited no observable damage up to the testbed limit of 130 J/cm². The top-performing optic was an HfO₂/SiO₂ stack deposited by ion-assisted deposition (23 layers), showed neither plasma nor damage to 130 J/cm², establishing a benchmark for ~10 ns at 2053 nm. Trends by deposition process, material system, substrate choice, and layer count are discussed, including strong performance for several densified coatings via ion beam sputtering and ion assisted electron-beam, weak performance for magnetron-based coatings in this dataset, and an apparent advantage for lower layer-count designs (~20–30 layers) among the highest performers.