Evolution of point defects in mechanical cracks of fused silica after CO<sub>2</sub> laser melting
Zhichao Liu, T. Tan, Feng Geng, Shengfei Wang, Jian Zhang, Hongjun Liu, Qinghua Zhang, Fei Fan, Jian Wang, Qiao Xu
Abstract
The traditional polishing method inevitably results in subsurface cracks in the fused silica, which seriously degrades their ultraviolet laser damage resistance. CO 2 laser irradiation can melt these cracks and improve their laser induced damage threshold (LIDT). Photoluminescence spectrum and SEM-FIB were employed to investigate the changes in the material microstructure at the crack location with CO 2 laser melting. The density of the oxygen-deficient centers of type II (ODC II) defects decreases, while the density of the non-bridging oxygen hole center (NBOHC) defects increases after high-temperature melting. The reason for this change is related to the dihydroxylation reaction and the participation of environmental oxygen in the defect type conversion. The reduction of ODC II defects is most likely the reason for the improvement of LIDT.