Nonvolatile Hologram Storage in BaTiO 3

A key obstacle to the development of high-capacity three-dimensional information mass storage systems using photorefractive crystals is that readout of holograms stored in the conventional manner is destructive. Thus hologram fixing in these materials is important if practical systems are to be built. High-temperature (801200C) photorefractive grating writing results for a variety of pure and doped barium titanate (BaTiO3) crystals are presented. Strong fixable secondary gratings were found to be correlated with increasing levels of Fe and Ni in doped crystals. Fixing was not observed in our pure crystals or those doped with V, Rh, or Co. Fixing was enhanced in an iron-doped crystal reduced by high-temperature annealing at low oxygen partial pressures, but not in reduced undoped, Co-doped or V-doped crystals. It was also found that the diffraction efficiency of a fixed grating in BaTiO3 is a strong function of temperature, grating period and crystal orientation. Diffraction efficiency was improved by at least two orders of magnitude (from 0.1% to 10% ) over earlier ionic fixing processes in BaTiO3. Lower temperatures lead to longer storage times. The ionic carriers forming the fixable gratings have thermally activated mobilities of 1.77 eV and 0.76 eV. Thesis Supervisor: Cardinal Warde Title: Professor of Electrical Engineering