Through in-situ measurements of surface and subsurface scratches in fused silica,the relationships between HF acid etching time and surface root mean square(RMS) roughness,as well as width and depth of scratches are investigated.The damage thresholds are also tested on fused silica after etching for different time.The results show that the surface RMS roughness,width and depth increase with the etching time.The damage threshold is increased when the etching time is from 1 min to 10 min,while it is decreased...