Generation and Recombination of Defects in Vitreous Silica Induced by Irradiation with a Near-Infrared Femtosecond Laser

Properties of defects induced by irradiation with a near-infrared femtosecond laser beam into vitreous silica are reported. Three photoluminescence bands with photon energy of 1.9, 2.7, and 4.4 eV were observed under an excitation of 5.0 eV. An isochronal annealing experiment revealed that unrelaxed oxygen vacancies ODC(II) and interstitial oxygen were generated as dominant species during the irradiation. In the annealing, diffusion of the interstitial oxygen was thermally activated, leading to a direct reduction of oxygen-deficiency-related defects such as ODC(II) and E‘ center. The concentration of oxygen-excess-related defects such as peroxy radicals, together with nonbridging oxygen−hole centers, increased first with annealing then decreased with the exhaustion of oxygen and their precursor, the E‘ center. The recombination of oxygen vacancies with interstitial oxygen is characterized as the major process occurring during the annealing.