The lifetime of silica optics in high power laser facility as the Laser MégaJoule (LMJ) is typically limited by the initiation of surface damages and their subsequent growth. To prevent this problem, a mitigation technique is used: it consists in a local melting of silica by CO2 laser irradiation on the damage site. Because of the difficulty to produce efficient mitigated sites with large depth, the characterization of damage site to mitigate is very important. In this context, confocal microscopy appears to be an efficient solution to detect precisely cracks present under the damage site.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.