Optical absorption defects created in SiO2 by Si, O and He ion irradiation

Three types of fused silica with different OH and impurity content (KU1, KS-4V and Infrasil 301) have been irradiated with high energy ions: Si4+ (24.37 MeV), O4+ (13.5 MeV) and He+ (2.46 MeV), at different fluences (from 5 × 1012 to 1.6 × 1015 ions/cm2). After ion implantation the optical absorption of the samples was measured at room temperature from vacuum ultraviolet (VUV) to near infrared (NIR). A saturation of the absorption spectra was observed in the samples implanted with Si and O when fluence increases, which indicates a defect density saturation with the ion fluence. A surface cracking was observed in all samples irradiated with Si and O ions at fluences (ion beam shutdown) corresponding to energy densities of irradiation between 1023 eV/cm3 and 1024 eV/cm3. No macroscopic cracks were detected at fluences for which an optical absorption saturation was reached.