Investigation of laser-induced damage threshold improvement mechanism during ion beam sputtering of fused silica

Abstract

In this paper, the influence of ion beam sputtering (IBS) process on laser damage resistance as a function of sputtering depth and typical defects which associated with laser damage performance was investigated. Damage test results reveal that the damage resistance of HF etched surface can be further enhanced about 30% by appropriate IBS removal depth (less than ~1000nm). Within this removal depth, the IBS process can remove the redeposited reaction products during HF acid etching process, improve surface quality and reduce chemical structure defects concentration. However, further ion sputtering often results in a decrease rather than an increase of damage threshold with enhanced surface densification and increased chemical structure defects of ODC and NBOHC which generated from sputtering damage. Moreover, the sputtered surface will accelerate the chemical reaction of surface atoms with water molecules. Thus the newly obtained hydroxylation layer rich in highly absorptive products can result in the decrease of laser damage resistance. The study reveals the improvement mechanism by IBS process, and provides both technical guidance and theoretical basis for the optimization of the post-process of fused silica.