Double-doped batio.sub.3 crystal for holographic storage

Abstract

A new photorefractive material comprises BaTiO.sub.3 double-doped with two dopant species, both of which have at least two valence states, with one of the dopant species (e.g., cerium) having an ionization level that is near the middle of the barium titanate bandgap and the other dopant species (e.g., rhodium) having an ionization level that is closer to the valence band edge of barium titanate, such that both dopant species are sensitive to visible light, but only one dopant species (the one closer to the valence band edge) is sensitive to infrared radiation. The double-doped BaTiO.sub.3 provides a unique combination of photorefractive properties, thereby improving its performance as a holographic storage medium. The double-doped barium titanate crystal is employed as a holographic recording element. The double-doped barium titanate crystal has a dark storage time at room temperature of several years or more and may be nondestructively read out at an infrared wavelength. Recording information on the double-doped barium titanate crystal is done by first sensitizing the double-doped barium titanate crystal with a substantially uniform beam of radiation at one wavelength and then either simultaneously or subsequently storing information in the barium titanate crystal with an incident recording beam that has a wavelength that is longer than that of the sensitizing beam. Nondestructive read-out is accomplished using only the second (writing) beam.