Dependence of defects induced by excimer laser on intrinsic structural defects in synthetic silica glasses

Effects of intrinsic defects on defect formation by excimer-laser irradiation were examined in synthetic silica glasses prepared by different methods. In samples containing oxygen-deficient centers (ODC’s), laser-induced E’ centers were stable at room temperature. In contrast, in samples heat treated in ${\mathrm{H}}_2$ atmosphere, in which almost all ODC’s changed into Si-H bonds, the induced-E’-center concentration increased by about two orders of magnitude, and the resulting E’ centers were unstable, decaying at room temperature. We thus conclude that the formation efficiency of E’ centers from Si-H bonds is much higher than that of ODC’s and that the induced-E’ centers recombine with radiolytic molecular ${\mathrm{H}}_2$ to restore Si-H bonds. It is suggested that a trace amount of Si-H bonds plays an essential role in defect creation and annihilation in OH-containing silica glasses.