Formation of redeposit in chemical etching process of fused silica and its effect on laser-induced damage

Chemical etching is one of the major post-processing techniques to improve laser-induced damage performance of fused silica optics, but deposits adhered to the surface of etched optics affect the surface quality, transmission performance and laser-induced damage resistance of fused silica a lot. In this work, optical microscope and atomic force microscope (AFM) were used to characterize the surface morphology of deposits adhered to the etched surface of fused silica. In addition, the formation process of the deposits was analyzed. Energy dispersive X-ray analysis shows that deposits adhered to the surface of etched fused silica are mainly composed of metallic salts of Fe, Ni and Al elements. Damage threshold test results show that the areas with high density deposits on fused silica surfaces have lower damage thresholds than the areas with few deposits. So redeposits adhered to the etched surface have the great influence on laser damage performance of fused silica, they are precursors inducing laser-damage of fused silica.