Removal of scratches on fused silica optics by using a CO₂laser

We investigate the efficiency of local CO₂laser processing of scratches on silica optics in order to enhance the nanosecond UV-laser damage resistance. The surface deformations induced by the process have been measured for different CO₂laser parameters and then the pulse duration and the beam diameter have been chosen accordingly to limit those deformations below 1 µm. From the study of the laser damage resistance as a function of different material modifications we identify a range of optimal radiation parameters allowing a complete elimination of scratches associated with a high threshold of laser damage. Calculation of the temperature of silica using a two-dimensional axi-symmetric code was compared with experiment, supporting an optimization of the laser parameter as a function of the maximal dimensions of scratches that could be removed by this process.