Influence of secondary treatment with CO2 laser irradiation for mitigation site on fused silica surface**Project supported by the National Natural Science Foundation of China (Grant Nos. 61505170, 61505171, and 51535003), the Joint Fund of the National Natural Science Foundation of China, the Chinese Academy of Engineering Physics (Grant No. U1530109), and the China Postdoctoral Science Foundation (Grant No. 2016M592709).

Abstract

The ablation debris and raised rim, as well as residual stress and deep crater will be formed during the mitigation of damage site with a CO2 laser irradiation on fused silica surface, which greatly affects the laser damage resistance of optics. In this study, the experimental study combined with numerical simulation is utilized to investigate the effect of the secondary treatment on a mitigated site by CO2 laser irradiation. The results indicate that the ablation debris and the raised rim can be completely eliminated and the depth of crater can be reduced. Notable results show that the residual stress of the mitigation site after treatment will reduce two-thirds of the original stress. Finally, the elimination and the controlling mechanism of secondary treatment on the debris and raised rim, as well as the reasons for changing the profile and stress are analyzed. The results can provide a reference for the optimization treatment of mitigation sites by CO2 laser secondary treatment.