Physical Disorder and Optical Properties in the Vacuum Ultraviolet Region of AmorphousSiO2

The optical absorption of point-defect-free ${\mathrm{SiO}}_2$ glass in the vacuum ultraviolet region is primarily controlled by the concentrations of three- and four-membered ring structures composed of heavily strained Si-O-Si bonds. The main channel of color center formation by ${\mathrm{F}}_2$ excimer laser (7.9 eV) irradiation is not Frenkel-defect generation of oxygen via two-photon absorption processes but a pair generation of $E^{\prime }$ and nonbridging oxygen hole centers by the one-photon excitation of these strained bonds with 7.9 eV photons.