Quasi-Nondestructive Readout of Holographically Stored Information in Photorefractive Bi12SiO20 Crystals

We report the existence of a room temperature hologram fixing process in certain Bi12SiO2 (BSO) crystals, which appears to be due to the formation of a complementary grating of positive charges that compensates the photo-induced electronic space-charge field(1,2). Uniform illumination of the crystal with green light, in presence of an external D.C. electric field, erases the deep-level electronic charge pattern and reveals the positive charge grating which then decays with its own characteristic decay time. We believe, in agreement with the work of Strohkendl(3), that the hole charge pattern involves shallow traps. Since these traps can be thermally activated, the decay time constant can be further increased significantly by lowering the crystal temperature.