Enhanced nanomechanical properties of fused silica surface by wet etching and its implication on laser induced damage

Abstract

Wet etching of fused silica is known to alter its surface quality and optical performance, but its correlation with nanomechanical properties remains unclear. In this study, the effect of typical wet etching (KOH and HF) on nanomechanical and surface quality of fused silica is investigated with nanoindentation, water contact angle measurments, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Experiment results show that as the wet etching depth increases from 1 μm to 5 μm, the concentration and depth of metallic contamination in fused silica surface decreases significantly, and the water contact angle of fused silica surface also decreases. In contrast, the elastic modulus and nanohardness of fused silica surface increases with etching depth. Further analyses indicate the reduced concentration and depth of metallic contamination, along with the increased densification in fused silica surface, are responsible for the enhanced nanomechanical properties. Moreover, the correlation between the densification and laser induced damage threshold of fused silica is discussed. These findings advance the understanding the nanomechanical properties of fused silica and provide insights for optimizing the optical fabrication process and extending the lifespan of fused silica optics used in intense laser systems.