Polarization holograms and diffraction anisotropy in amorphous chalcogenides

Abstract

Polarization hologram recording based on the effect of photoinduced anisotropy (PA) is reviewed, focusing on amorphous chalcogenides (ACh). Possible PA mechanisms in ACh are considered. Polarization holographic grating recording in amorphous As?S?Se (a-As?S?Se) films is experimentally studied and analysed in comparison with scalar recording. It is holographically established that linearly polarized 632.8 nm light produces photoinduced anisotropy and the chalcogen related D+, D? centre reorientation and generation mechanism is proposed. It is used to explain the observed peculiarities of polarization (vector) recording in comparison with scalar recording based on photoinduced structural changes: much lower diffraction efficiency (4 ? 10?3?% versus?4%), much larger specific recording energy (6400?J/(cm2?%) versus 20?J/(cm2?%)), difference in spatial frequency response, instability (vector hologram lifetime of about two days versus practically permanent scalar holograms), the absence of hologram self-enhancement (present in scalar recording), and near perfect reversibility. It is also experimentally found that light diffraction from the polarization holographic gratings in a-As?S?Se films is indeed anisotropic since the readout wave polarization diffracted in the minus first order is changed in such a way that the linear signal wave polarization orthogonal to the reference wave polarization is reconstructed. The results obtained are discussed.