Spectroscopic investigation of SiO2 surfaces of optical materials for high power lasers

High quality surfaces of fused silica optical materials were studied using microscopic fluorescence imaging as well as Raman and emission micro-spectroscopy. For as-polished surfaces optically active defect formations were detected on the surface of the material which vary in geometry, relative intensity and concentration depending on the polishing process. A partial correlation of these defects with subsequent laser damage sites was indicated. Following laser-induced damage the Raman and photoluminescence spectra indicated extensive material modification within the damage site. Emission spectra show at least three characteristic luminescence bands centered at 1.9 eV (650 nm), 2.2 eV (560 nm) and similar to 4.7 eV (similar to 440 nm). Raman scattering indicates that laser irradiation leads to compaction.