F2 laser ablation process of silica glass

The laser ablative figuring of the silica glass has been investigated experimentally. F2 laser and ArF excimer lasers are used as the laser light source for efficient ablation of silica glass material. The output beam of F2 and ArF laser were focused on to the surface of silica glass plate. The ablation rate were measured by a surface profilometer. The process on the surface was done by scanning in X-Y direction and a uniform ablation was observed. However the surface roughness was large as compared with the case of PMMA. The waveform of incident and transmitted laser light was measured by high speed photo-tubes to observe the time dependence of the absorption. The measured waveform indicates that the absorption was small at the leading edge of the laser pulse, and a strong ablation was induced at the latter part of laser pulse due to the excited state absorption. These phenomena are quite similar to both in F2 and ArF laser light. We have developed a simple model in which the instantaneous absorption is defined by the absorbed energy prior to the moment.