Influence mechanisms of the “Si-enrichment” phenomenon and the consequent rapid increase of damage-triggering electronic defects on laser damage resistance of fused silica

First-onset intense laser-induced damage of fused silica and other optics would cause severe damage propagation and rapid component failure within a short subsequent period. Although this ubiquitous phenomenon has been widely acknowledged, its traceable dominant causes and corresponding action mechanisms remain undetermined. It hinders further understanding of and effective solutions to the rapid scrapping of damaged optics. In this study, the special and critical first-onset damage products (local “Si-enrichment” regions) in the plasma-induced phase-change zones were first discovered. Interestingly, these hazardous first-onset damage products were also identified on damaged BK7 glass surfaces, suggesting a previously unrecognized universal effect. Based on steady-state photoluminescence spectrum/imaging characterization, laser-induced damage tests, elemental analysis and photoelectron theories, the influence of “Si-enrichment” regions was systematically studied. The occurrence of “Si-enrichment” regions significantly increased the densities of various absorbing electronic defects (ODCII, STE, E’-Center and NBOHC) and the proportions of more hazardous electronic defects (ODCII and STE) containing more seed electrons, seriously weakening the laser damage resistance of optical components. Based on the TRPP detection, the developed electron excitation model under defect levels, and thermal-plasma-induced damage molecular dynamics simulation, the formation mechanisms of “Si-enrichment” regions were revealed. These regions would form in phase-change damage zones within ∼ ns after damage initiation. The “explosive” phase-change-induced elemental decomposition converted massive covalent Si and O elements into corresponding free states, which constituted the first cause of the formation of “Si-enrichment” regions. Active free-state O atoms could combine to form the oxygen gas released into the air, resulting in significant loss of O elements. In contrast, massive relatively stable Si elements could ultimately deposit on damaged surfaces, causing the “Si-enrichment” phenomenon. This constitutes the second cause of the formation of “Si-enrichment” regions. To sum up, this work determines the traceable dominant causes of the rapid scrapping issues of damaged optics and corresponding action mechanisms. It is meaningful for understanding and addressing the damage-induced rapid scrapping issues of fused silica and other agnate silicate glass applied in intense laser fields.