Scratch Types and Damage Thresholds of Fused Silica

Atom force microscopy (AFM) is used to investigate micro-morphology of various types of scratches in the fused silica surface and sub-surface. Based on the shape, scratches can be classified as lateral scratch, radial scratch, Hertizan cone scratch, and trailing indent scratch. From forming mechanism, scratches can be classified as plastic scratch, brittle scratch and mixed scratch. The statistical damage thresholds of three kinds of common scratches are obtained through raster scanning at different laser fluences. The results show that the damage threshold of radial scratches is the highest and that of the trailing indent scratches is the lowest. In addition, for the samples etched in different concentration buffered hydrofluoric acid solutions for different etching time, the damage thresholds are also obtained. The high concentration and long-time etching can effectively enhance the damage threshold of scratches. Brittle scratches are easier to damage than plastic scratches. Two kinds of mechanisms are responsible for the laser damage: local electrical intensification and mechanical weakness induced by scratches. This work is a reference for further investigation on damage threshold enhancement and damage mechanism of scratches in fused silica.