In-situinvestigation of damage processes on fused silica induced by a pulsed 355nm laser with high repetition rate

Abstract

Pulsed lasers with high repetition rate have attracted more and more attention in recent years, due to the increased demand in many fields, including industrial applications such as laser processing and micromachining. However, the damage thresholds of optics exposed to high repetitive laser pulses, especially at the 355 nm wavelength, remain a major concern. Previous work about laser damage in optics was performed mainly by using pulsed lasers with 1-on-1 test or N-on-1 test but with very low pulse repetition rate (for example, from several Hz to hundreds of Hz). The results obtained, however, cannot be directly extended to analyze and understand the damage processes induced by high repetitive laser pulses. In this paper, we present our recent progress on investigation of damage processes on fused silica induced by a pulsed 355 nm laser with high repetition rate. By using a system based on photothermal effect, we have realized in-situ monitoring of laser-material-interaction dynamics through measuring the laser-induced absorption evolution. The results demonstrate that the initiation of laser-induced damage process occur far before any physical damage observable using high-resolution optical microscopes. The damage processes typically are long term accumulation effects of laser-induced increase in absorption, that itself is depending on both the irradiation fluence and repetition rate. The photothermally measured results are also compared with results obtained by using light scattering technique. The results show that such a photothermal technique is a very useful tool for in-situ studies of the damage process induced by high repetitive laser pulses at 355 nm wavelength.