Fused silica optics were treated by dynamic etching using buffered hydrofluoric acid (BHF) with different etching depths. The transmissivity of fused silica slightly increases in deep UV (DUV) range after dynamic etching. Surface qualities of fused silica were characterized in terms of surface roughness, surface profile and photoluminescence (PL) spectra. The results show that dynamic etching has a slight impact on surface RMS roughness.PL defects gradually reduces by dynamic etching, and laser damage resistance of fused silica continuously increases with etching depth extending. When removal depth increases to ~12μm, the damage threshold is the double that of the unetched surface. However, surface profile continuously deteriorates with etching depth increasing. Appropriate etching amount is very important for improving damage resistance and mitigating surface profile deteriorating of fused silica during etching process simultaneously. The study is expected to contribute to the practical application of dynamic etching for mitigating laser induced degradation of fused silica optics under UV laser irradiation.
The laser-induced damage of fused silica optics significantly restricts the output ability of large laser systems. Hydrofluoric (HF)-based etching is an effective processing to eliminate impurities and mitigate subsurface defects. Traditional polished fused silica samples were etched for different time in a HF-based etchant (2.3% HF and 11.4% NH4F) assisted by a 1.3 MHz megacoustic field. The laser-induced damage thresholds (LIDT) were measured by R-on-1 method, and fourier transform infrared absorption spectras of the samples were obtained. The results of the LIDT demonstrated that the LIDTs of the fused silica samples increased after megacoustic field assisted etching. The more surface materials were removed, the higher LIDT was obtained. The analysis of the infrared spectra illustrated that structural densification materials were removed during the etching, and thus the LIDT can be improved.
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