Sub-bandgap light hologram recording in amorphous chalcogenides

Sub-bandgap light recording (SBLR) of holograms is studied basing on the experiments in a-As2S3 films and literature data. Holographic grating recording with focused (light intensity I = 14 - 124 W/cm2 ) and unfocused (I = 0.50 - 0.78 W/cm2) 632.8 nm He-Ne laser sub-bandgap light in non-annealed and annealed a-As2S3 films has been experimentally studied. The focused light recording is found to be much more efficient (diffraction efficiency up to 14.9%, specific recording energy down to 216 J/(cm2%)) than the unfocused light recording (0.11%, 72400 J/(cm2%)). Some other properties are also different. The focused light recording is explained by the photothermally stimulated relaxational structural changes (RSC) accompanied by the photoinduced generation and recharging of D-centers. The unfocused light recording is explained by the photorientation of D-centers with some contribution of RSC . SBLR in materials other than a-As2S3 films was considered and the conclusion was made that amorphous sulfides and selenides are expected to be the best SBLR recording materials. SBLR is advantageous because of its bulk nature enabling the production of homogeneous holographic optical volume elements and devices.