Distribution of Inclusions in Fused Silica Sub-Surface and Its Influence on Laser-Induced Damage

Fused silica with different etching time were obtained by HF acid etching. The variation and distribution of inclusions were analyzed by synchrotron X-ray fluorescence spectrometry. The relative concentrations of main inclusions, such as Fe, Cu and Ce, are decreased with the increase of etching time. The AFM and Wyko images of the samples show that the surface roughness increase with the increase of etching time. The R:1 test procedure has been adapted to the pre-etching samples. The laser induced damage threshold (LIDT) increases within 30 min etching time and rapidly decreases to the threshold of non-etching fused silica level. The result indicates that Cu, Ce concentrations plays important role at low etching time, whereas when etching time is too long, the decreased LIDT is attributed to the increment of surface roughness.