Optical anisotropy in As2S3 glass induced with sub-bandgap illumination

Mechanism of photoinduced anisotropy in chalcogenide glasses

“…16 He has proposed that isotropic dielectric tensors characterizing annealed glasses become anisotropic with illumination, since structural elements having the tensor components parallel to the electric field of illumination are excited preferentially, which may be rotated to other directions when relaxed. Therefore, consistent with experimental observations, 10,19 the negative anisotropy is induced; that is, the birefringence ⌬nϭn( ʈ )Ϫn(Ќ) and the dichroism ⌬␣ ϭ␣͑ ʈ ͒Ϫ␣͑Ќ͒ are negative, where n is the refractive index at transparent wavelengths and ␣ is the absorption coefficient at around optical absorption edges, and the symbols ʈ and Ќ refer to the electric field vectors of probe light parallel and perpendicular to that of excitation light.…”

“…19 Probe light was provided from a He-Ne laser, the photon energy and the intensity being 2.0 eV and ϳ1 mW/cm 2 . In this instrument, the phase difference between the two orthogonally-polarized light transmitted through a sample could be measured.…”

“…Chalcogenide glasses are known to exhibit a variety of photoinduced phenomena, 1-4 among which the photoinduced anisotropy 5,6 has aroused considerable interests in fundamental [7][8][9][10][11][12][13][14][15][16][17][18][19][20] and applied researches. 21,22 The phenomenon refers to the observations that chalcogenide glasses exhibit optical anisotropies, i.e., birefringence and dichroism, when exposed to linearly polarized light.…”

“…It is also demonstrated very recently that even circularly or unpolarized light can induce the anisotropy, if light is incident upon a sample from sideward directions. 16,17,19 The mechanism of the photoinduced anisotropy can be understood in a phenomenological sense through Fritzsche's model. 16 He has proposed that isotropic dielectric tensors characterizing annealed glasses become anisotropic with illumination, since structural elements having the tensor components parallel to the electric field of illumination are excited preferentially, which may be rotated to other directions when relaxed.…”

“…9,12 In a model, which may be termed as the crystalline model, structural elements similar to, but not necessarily the same with, the corresponding crystalline structure are assumed to be oriented with illumination. 5,6,8,19 In order to elucidate the microscopic mechanism of the photoinduced anisotropy, the structural element responsible for the optical anisotropy should be revealed. The present experimental studies including x-ray and birefringence measurements for elemental and stoichiometric chalcogenide glasses strongly suggest that the crystalline model is more plausible.…”