Removal of scratches on fused silica optics by using a CO 2 laser

We investigate the efficiency of local CO2 laser 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 CO2 laser 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.