Round-robin measurements of the laser-induced damage threshold with sub-picosecond pulses on optical single layers

The standardization and comparison of laser-damage protocols and results are essential prerequisites for development and quality control of large optical components used in high-power laser facilities. To this end, the laser-induced-damage thresholds of two different coatings were measured in a round-robin experiment involving five well-equipped damage testing facilities. Investigations were conducted at the wavelength of 1 mu m in the sub picosecond pulse duration range with different configurations in terms of polarization, angle of incidence, and environment (air versus vacuum). In this temporal regime, the damage threshold is known to be deterministic, i.e., the continuous probability distribution transitions from 0 to 1 over a very narrow fluence range. This in turn implies that the damage threshold can be measured very precisely. These characteristics enable direct comparison of damage-threshold measurements between different facilities, with the difference in the measured values indicating systematic errors or other parameters that were not previously appreciated. The results of this work illustrate the challenges associated with accurately determining the damage threshold in the short-pulse regime. Specifically, the results of this round-robin damage-testing effort exhibited significant differences between facilities. The factors to be taken into account when comparing the results obtained with different test facilities are discussed: temporal and spatial profiles, environment, damage detection, sample homogeneity, and nonlinear beam propagation. (C) 2020 Society of Photo Optical Instrumentation Engineers (SPIE)