Effects of laser conditioning with different pulse widths on picosecond laser-induced damage resistance in HfO₂/SiO₂ high-reflectivity coatings

Current optimizations in the fabrication processes of multilayer dielectric (MLD) high-reflection (HR) coatings remain difficult to meet the demand for picosecond (ps) laser damage resistance in high energy petawatt laser systems. This study pioneers a systematic investigation of laser conditioning (LC) effects on electron beam (e-beam) HfO2/SiO2 HR coatings using 250 ps, 500 ps, 800 ps, and 10 nanosecond(ns) laser pulse widths. Results demonstrate a 13% enhancement in the laser-induced damage threshold (LIDT) under ~10 ps laser irradiation for 500 ps conditioned samples compared to those unconditioned, while negligible LIDT variations are observed for other pulse widths. While defect density and the damage types in samples exhibit no statistically alteration. This indicates that nanoscale defects are not eliminated by LC, but only increased their LIDT. A physical model of the interaction between sub-ns laser pulses and localized defect states is proposed, combining ionization rate equations with the two-temperature model (TTM). Thereby revealing the improvement mechanism of 500 ps LC on the ps laser-induced damage resistance of the samples. This work provides new strategies and practical methodologies for enhancing the ps laser-induced damage resistance of MLD HR coatings.