Combined non-destructive evaluation of the damage precursors in fused silica optics

Combined non-destructive evaluation methods for fused silica's damage precursors including UV photothermal weak absorption, ultrafast fluorescence, steady-state fluorescence, Raman spectroscopy, and stress distribution, are proposed to explain the damage mechanism from multiple perspectives. The correlation between each non-destructive characterization method and damage behaviors is simultaneously verified, in general, the damage threshold test of R on 1. The results have shown that regions with high photothermal absorption are accompanied by low damage thresholds, because the photothermal conversion process is associated with laser-induced damage. The damage threshold is also lower at locations of bright ultrafast fluorescence signals with a lifetime ranging from 1.2∼3 ns, as ultrafast fluorescence is associated with high densities of defects. A complementary relationship between the distribution of ultrafast fluorescence and the distribution of photothermal absorption signals is constructed. This indicates that the steady-state fluorescence cannot accurately evaluate the precursor's damage performance. Furthermore, Raman spectroscopy is utilized to identify the structural changes in bond lengths and angles, as well as locations of damages coinciding with stress distribution.