Determination of photobleaching rate and its application in quantitatively evaluating the fracture degree of fused silica optical surfaces

Photoluminescence detection is a promising approach to characterize electronic structural defects (i.e., point defects) in optical components and non-destructively predict their anti-laser damage performance via pump laser-excited photoluminescence properties, facilitating defect repair and optics recycling. However, photoluminescence intensity declines drastically under continuous excitation (i.e., photobleaching). Meanwhile, photoluminescence properties are highly sensitive to the differences in point defects dominated by surface fracture, which determines the laser damage resistance of optical surfaces. Clarifying the effect of fracture degree on photoluminescence properties, especially photobleaching, is crucial for efficiently and non-destructively identifying the defects that degrade optical performance. Herein, how surface fracture degree affects photoluminescence intensity and photobleaching rate is investigated to support fracture degree quantification. It is innovatively found that photoluminescence intensity decreases biexponentially with excitation duration (R² = 0.99), and its initial intensity (t = 0 s) is positively linearly correlated with the stable intensity. Meanwhile, photobleaching rate (k) is proposed to describe the process. Surprisingly, the initial intensity, stable intensity, and k all increase with material fracture degree, supporting their utility as quantitative indicators of defect brittleness. Notably, variations in the stable intensity among fractured surfaces are modest, making it only applicable to preliminary determination of surface fracture via this parameter. Furthermore, regular Raman intensity drift with excitation duration also verifies the prominent photobleaching of fractured surfaces. This work develops three indicators for optical surface fracture degree, effectively mitigating photobleaching-induced inaccuracies and providing robust support for reliable non-destructive evaluation of laser damage resistance via photoluminescence detection.