Brittle scratches (microcracks) are important damage precursors to fused silica optics under 351/355nm laser irradiation. HF-based etching is an economical way to mitigate the influence of scratches on laer-induced damage. In this paper the authors describe how they employed ultrasonic/megasonic-assisted HF etching to alleviate the damage precursors. Samples were treated by being submerged into 6 wt% HF solution under various conditions, that is, without acoustic power and with acoustic power at different powder density to etch various materials away from fused silica surfaces. The evolution of scratch morphologies was monitored and damage performance tested against the surfaces without brittle scratches (control samples). The results show that the scratches can be enlarged and the microcracks can be opened and blunted by means of wet chemical etching. Around 25um material removal is sufficient to remove the lateral cracks that accompany the brittle scratches. It is shown that wet chemical etching can increase the laser-induced damage threshold (LIDT) at the scratches up to a factor of 1.77, while the addition of acoustics has marginal effects on the LIDT. However, the acoustic-assisted etching can increase slightly the etching rate of fused silica and more powerful acoustics can lead to a little higher etching rate.
