Model of holographic recording in amorphous chalcogenide films using subband-gap lightat room temperature

The subband-gap light holographic recording in amorphous as-evaporated ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ films at room temperature is experimentally studied. Properties are considerably different from those of usual holographic recording based on the band-gap light induced structural changes. The most important characteristic features of this nonpermanent recording include photoinduced refractive index increase, weak photobleaching, the absence of the photoinduced thickness changes, light polarization dependence, large exposures, holographic grating shifts during the exposure and a peculiar two maxima spatial frequency response. The first order diffraction efficiency up to 4.1% is achieved. These features as well as possible recording mechanisms are discussed. A subband-gap light holographic mechanism is proposed based on the photoinduced reorientation and generation of chalcogenide related ${\mathrm{D}}^{\mathrm{-}}$ and ${\mathrm{D}}^{+}$ centers counteracted by the photostimulated relaxational structural changes. The results obtained for amorphous ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ films can be applied also to other amorphous chalcogenide films.