Anisotropic structural change induced by sub-bandgap lights in As-S glasses studied by low-frequency Raman scattering

Changes in low-frequency vibrational modes with illumination of linearly po larized sub-bandgap light have been investigated by monitoring the formatio n of Bragg gratings in As-S glasses in order to determine photoinduced anis otropic structural rearrangements in a mesoscopic region. We found that the low-frequency vibrational modes show an intriguing change to us, which we suggest is some mesoscopic structural anisotropy due to fragmentary rearran gements induced by polarized sub-bandgap light. The relaxation dynamics of the anisotropic structural rearrangements have also been studied by erasing the Bragg gratings at a temperature lower than the glass transition temper ature. We suggest that the thermokinetic structure of the relaxation is low -dimensional and the cooperatively rearranging regions an anisotropic. (C) 2000 Elsevier Science B.V. All rights reserved.