Ultraviolet laser-induced damage growth characteristic and mechanism on the surface of fused silica

The growth of laser induced damage on the surface of fused silica plays a major role in determining the operation fluence and optics lifetime in high power laser system. In this paper, the damage growth characteristic of fused silica and possible growth mechanisms were investigated. The morphology of damage site was measured by scanning electron microscopy (SEM) and optical microscopy (OM). The finite difference time domain (FDTD) method was used to calculate the electric field distribution around the damage site. Furthermore, energy dispersive spectrometers (EDS) micro-analysis technique, x-ray photoelectron spectrometer (XPS) and Raman spectroscopy were applied to detect the chemical composition, point defect and microstructure of damage site in order to explore the growth mechanism. It's found that the growth threshold is greatly affected by the size of damage site, and the growth threshold of damage site is much lower than that of undamaged area. Theoretical calculation demonstrated that the rough damage site can strong modulate the distribution of electric field and result in the enhancement of local light field around the damage site. Results also showed that the oxygen defect was generated and the structure was changed after initial laser damage. Based on the above analysis, a mechanism of laser-induced damage growth on fused silica surface was proposed.