Laser-induced damage-growth threshold at 351 nm in the nanosecond regime in dielectric coatings employing different high-index materials

The laser-damage performance of HfO₂/SiO₂ and Al₂O₃/SiO₂ mirrors was investigated at a laser wavelength of 351 nm with nanosecond pulse durations. A method was developed to quantify the laser-induced damage-growth threshold under conditions relevant to high-repetition-rate, large-aperture laser systems. The results suggest that the damage-growth performance cannot be inferred from the corresponding damage-initiation threshold that is commonly used to evaluate the performance of optical materials. A systematic difference was also observed in the performance between these two groups of high-index materials, with the Al₂O₃/SiO₂ mirrors exhibiting about twofold improvement in the damage-growth threshold.