Photoinduced deformations in chalcogenide glasses: What are the driving forces?

Chalcogenide glasses including As2S3 and Se are known to exhibit a variety of photoinduced deformations such as volume expansions, anisotropic shape changes, and surface ripples. These deformations are produced by photoinduced viscous material flows which are caused by some driving forces, while the origins are controversial. We propose a guiding idea that the driving force arises from atomic and optical mechanisms; the former from structural disordering and intermolecular alignment and the latter from radiation force and torque. Previously proposed models such as Coulombic and electric-gradient forces are criticized. We also compare these deformations with those in azobenzene-containing organic materials.