Vacuum-Induced Deoxygenation and Dehydroxylation Mechanisms Drive Point Defect Evolution in Laser-Irradiated AR Coatings

Abstract

The significant degradation of the laser-induced damage threshold (LIDT) of optical coatings under vacuum environments poses a critical bottleneck for high-power space laser systems, as the underlying atomic-scale point defect evolution mechanisms remain unclear. This study integrates multi-scale characterization with reactive force field molecular dynamics (ReaxFF-MD) simulations to elucidate the environmental dependence of point defects and their impact on laser damage behavior, with a systematic focus on oxygen loss, dehydroxylation, and the evolution of the non-bridging oxygen hole center (NBOHC). The results show that point defect propagation is significantly enhanced under vacuum compared to air, leading to more severe LIDT degradation. Laser irradiation induces surface oxygen loss in the form of O2 molecules, accompanied by the formation of oxygen-related defects dominated by ODC(I), which exhibit more pronounced concentrations under vacuum. Meanwhile, dehydroxylation driven by the condensation of adjacent Si-OH predominantly releases H2O molecules and introduces defect precursors rather than directly propagating the NBOHC. The evolution of the NBOHC is governed by the interplay between propagation and reduction paths. Under low-power irradiation, the evolution of the NBOHC is dominated by multipath reduction, primarily forming defect precursors with an E’center, with a secondary contribution from Si5 and E’center recombination, whereas very few peroxy linkages (POLs) are formed via NBOHC coupling. Under high-power irradiation, it is dominated by precursor-driven propagation, with the propagation rate under vacuum being approximately 115% higher than that in air. This study provides the first insight into the evolution mechanisms of oxygen loss and dehydroxylation under vacuum, establishing a theoretical foundation for enhancing the laser damage resistance of optical components in extreme environments.