Non-destructive evaluation of UV pulse laser-induced damage performance of fused silica optics

Jin Huang,Qingzhi Li,Wanguo Zheng,Hongjie Liu,Dunlu Sun,Xiaodong Jiang,Xin Ye,Laixi Sun,Fengrui Wang,Weidong Wu,Feng Geng

doi:10.1038/s41598-017-16467-2

Abstract

The surface laser damage performance of fused silica optics is related to the distribution of surface defects. In this study, we used chemical etching assisted by ultrasound and magnetorheological finishing to modify defect distribution in a fused silica surface, resulting in fused silica samples with different laser damage performance. Non-destructive test methods such as UV laser-induced fluorescence imaging and photo-thermal deflection were used to characterize the surface defects that contribute to the absorption of UV laser radiation. Our results indicate that the two methods can quantitatively distinguish differences in the distribution of absorptive defects in fused silica samples subjected to different post-processing steps. The percentage of fluorescence defects and the weak absorption coefficient were strongly related to the damage threshold and damage density of fused silica optics, as confirmed by the correlation curves built from statistical analysis of experimental data. The results show that non-destructive evaluation methods such as laser-induced fluorescence and photo-thermal absorption can be effectively applied to estimate the damage performance of fused silica optics at 351 nm pulse laser radiation. This indirect evaluation method is effective for laser damage performance assessment of fused silica optics prior to utilization.

Highlights

As the most commonly used ultraviolet (UV) optic material in large high-power laser facilities such as the National Ignition Facility in the United States, the Laser MegaJoule in France, and the ShenGuang (SG)III laser facility in China, transparent fused silica optics have many advantages, such as low absorption at UV wavelength, high chemical stability, and excellent anti-damage performance[1,2,3,4]
Magneto-rheological finishing (MRF), which is based on flexible machining, can decrease the sub-surface damage (SSD) induced by mechanical polishing and is an attractive post-process method[24,25,26]
The results indicate that laser-induced fluorescence imaging (LIFI) can reflect the influences of dynamic chemical etching and MRF on the sub-surface defects of fused silica optics

Summary

Introduction

As the most commonly used ultraviolet (UV) optic material in large high-power laser facilities such as the National Ignition Facility in the United States, the Laser MegaJoule in France, and the ShenGuang (SG)III laser facility in China, transparent fused silica optics have many advantages, such as low absorption at UV wavelength, high chemical stability, and excellent anti-damage performance[1,2,3,4]. Two main kinds of defects are responsible for inducing laser damage of fused silica[13,14,15], absorptive contaminants (e.g., Ce and La) in the Beilby layer from polishing and sub-surface damage (SSD) from grinding and/or polishing of brittle material surfaces These precursors could decrease the laser-induced damage thresholds by directly absorbing UV laser energy, reducing the mechanical strength, or providing a highly enhanced local optical field. By characterizing the absorptive defects of fused silica surface and clarifying the influence of defect parameters on the damage performance of fused silica, we can realize non-destructive evaluation of laser-induced damage performance for fused silica optics. We analyzed the quantitative relationship of absorptive defect parameters and laser damage performance, and demonstrated the process of realizing non-destructive evaluation of laser induced damage performance by characterization of absorptive defects

Methods

Results

Discussion

Conclusion