Role of atomic electronic structure defects in initiating laser-induced modification and failure of brittle-hard fused silica optics

Laser-induced modification and failure are prone to occur on fused silica surfaces, seriously restricting their high-performance applications. However, it remains challenging to predict where and which type of damage would occur under specific laser conditions since the dominant traceable micro-structures in fused silica and corresponding influencing mechanisms have not been determined. It hinders effective solutions for damage issues. Herein, the damage and steady-state photoluminescence features of fused silica were explored to determine the dominant micro-structures. Furthermore, the influence mechanisms of these micro-structures under laser irradiation were studied based on the developed electron-transition and particle-in-cell plasma simulation models. It was, to our knowledge, first found that the electronic structure defects could govern the occurrence and types of laser-induced modification/failure. Accordingly, a non-destructive modification/failure prediction strategy based on steady-state photoluminescence detection was first proposed, whose accuracy was more than 90%. Furthermore, it was found that the initial electronic structure defects and laser intensities jointly determine the steady-state free-electron densities. Two vital intrinsic critical free-electron densities were found and defined (“first” and “second” free-electron densities). We found that the initial electronic defects could only induce defect “slow proliferation” as the steady-state free-electron density is smaller than the first critical value. The stress-induced damage could be induced when the steady-state free-electron density reaches the first critical value. The plasma ablative damage would be caused as the steady-state free-electron density reaches the second critical value. This work is meaningful for addressing the laser-induced damage issues of fused silica and other similar silicate glass, which could promote their application in intense-laser fields.