Quasi-nondestructive readout of holographically stored information in photorefractive Bi12SiO20 crystals

Abstract

The hologram fixing process in a Bi₁₂ SiO₂₀ crystal arises due to the formation of a complementary grating of positive charges localized in shallow traps. Uniform illumination of the crystal with blue or green light erases the electronic charge pattern but leaves the positive charge grating undisturbed. Due to the smaller mobility lifetime product of holes, this grating decays at room temperature with a time constant that is much longer than that of the electronic grating. We show in this letter that the readout time constant can be further increased considerably by cooling the crystal. Images retrieved from a crystal kept at 0 °C temperature and under continuous illumination for a few hours are presented. The energy levels of the hole trapping sites involved in this process are found to be situated at 0.56 and 1.1 eV above the valence band.