Two-step gated holographic recording in photorefractive materials using cw lasers

DETAILED DESCRIPTION What is claimed: 1.
A method of writing to a holographic recording medium containing a ferroelectric material that contains no more than about 0.
01% atomic of an optically active impurity, the method comprising the following steps: separating a first radiation beam of a first wavelength into a reference beam and an object beam; spatially modulating the object beam to produce a spatially modulated object beam; combining the reference beam and the spatially modulated object beam to form an interference pattern on a first region of said holographic recording medium; and directing a gating radiation beam containing at least a second wavelength onto a second region at least partially coextensive with said first region of the holographic recording medium, whereby photons of the first and second wavelengths together promote electrons or holes of the hologaphic recording media to a conduction band or a valence band, respectively, by a two-photon process such that the interference pattern is recorded in said holographic recording medium, wherein at least one of the first radiation beam and the gating radiation beam is produced by a laser at an intensity of at most about 1000 watts/cm.
sup.
2, wherein said two-photon process employs intermediate states that are defects in the ferroelectric material, which intermediate states may be populated with said electrons or holes excited by radiation over at least a 50 nm range of wavelengths in the electromagnetic spectrum.
and wherein said first and second wavelengths are not in resonance with said optically active impurity.
2.
The method of claim 1 wherein the the laser is a continuous wave laser.
3.
The method of claim 1 wherein the laser provides radiation at an intensity of between about 20 and 200 watts/cm.
sup.
2.
4.
The method of claim 1 wherein the first radiation beam is produced by a continuous wave laser.
5.
The method of claim 1 wherein the gating radiation beam is produced by a continuous wave laser.
6.
The method of claim 1 wherein the ferroelectric material contains no more than about 10 parts per million of optically active impurity