Volume hologram recording and charge transfer process in Bi12SiO20 and Bi12GeO20

Bi12SiO20 and Bi12GeO20 are photoconductive and electro‐optic crystals in which hologram recording is performed using the photorefractive effect; their sensitivity and optical quality are comparable with the high‐resolution photographic plate. Hologram formation and erasure are analyzed in terms of a simple two‐level charge transfer model. The photocarrier’s displacement length, comparable with fringe spacing and the nearly unity quantum efficiency, allows the attainment of the ultimate photosensitivity. The trapping centers concentration being much smaller than the absorption centers concentration, the saturation recording time and diffraction efficiency are found limited only by the trap‐filling mechanism.