Photon energy dependence of vacuum ultraviolet light-induced stress in silica glass

The photon energy dependence of vacuum ultraviolet light-induced stress was investigated for two types of silica glass, type I (GE214) and type III (S uprasil P20). Samples of both glass types were irradiated under three condi tions: (1) with xenon (Xe) arc light directly, (2) through three kinds of f iltered Xe arc light, and (3) with a high-pressure mercury (Hg) lamp. To ev aluate the samples, the absorption spectra were measured in vacuum ultravio let (VUV), UV, and infrared regions. The irradiation-induced stress was als o measured. The relative shape of the Xe arc spectrum was derived, and the absorption spectra of GE214 and Suprasil P20 were determined in the VUV reg ion at the Xe lamp operation temperature. The measured stress was converted to strain energy, which was then corrected with respect to the hydroxyl gr oup (=SiOH) content and the irradiation time. The results revealed that the corrected strain energy was linearly proportional to the amount of absorbe d light within the measurement error. The photon energy threshold for induc ing the strain was evaluated to be 5.6 eV for GE214, at which the absorptio n coefficient was similar to 10 cm(-1). In contrast, light absorption occur red at photon energy not less than 6.5 eV for Suprasil P20. Therefore, ther e is a photon energy dependence on the VUV induced stress. This dependence varies not only with the type of silica glass but also its ambient temperat ure which, in turn, controls the absorption coefficient. In fact, the estim ated absorption coefficient at 7.5 eV and at 743 K for GE214 was about two orders of magnitude higher than that measured at room temperature. The bond cleavage and rearrangement of the silica glass network should be enhanced by heat. The analysis of these photon energy dependences also suggested tha t Suprasil P20 was strained more effectively than GE214, probably due to ab sorption of VUV light by = SiOH s contained in silica glass. (C) 1999 Ameri can Institute of Physics. [S0021-8979(99)02610-9].