Photoexpansion in As2S3 glass

Mechanisms of photoexpansion in chalcogenide glasses have been studied in three respects. A detailed x-ray investigation of As2S3 shows that the photoexpansion can be connected with asymmetric broadening of the first sharp diffraction peak. Comparison between radiation-induced volume changes and density ratios of glassy-to-crystalline forms in As2S3 and SiO2 implies that As2S3 can expand since the glass is as dense as its crystal. When As2S3 is exposed to illumination, the photoexpansion appears earlier and later than the photodarkening for bandgap and subbandgap illumination, respectively. These observations are discussed from a microscopic point of view.