Surface molecular structure defects and laser-induced damage threshold of fused silica during a manufacturing process.

Laser induced damage of fused silica is a serious problem for high power laser systems, and damage precursors are mainly induced by manufacturing processes. In this work, fused silica samples were prepared from a manufacturing process including grinding, polishing and etching procedures. The chemical disorder of the prepared samples was inspected by using fluorescence microscopy and ultra-violet fluorescence spectrometer. The physical disorder was characterized by using Infrared and Raman spectrometer. Laser induced damage thresholds (LIDTs) were measured in R-on-1 mode by 355 nm 6.4 ns laser pulse. Results showed that with the manufacturing processes transforming from grinding to etching, the magnitude of fluorescence point defects reduced while their types did not change, the Si-O-Si bonds of prepared samples were strained and the strained bonds were mitigated. The LIDTs increased with the reducing of fluorescence defects and strained Si-O-Si bonds. However, these structural defects can not be eliminated by the current manufacturing process. Improvements may be needed to eliminate the structural defects for a higher LIDT of fused silica.