Photorefractive systems and methods

The method of creating substantially permanent holograms in a photorefractive crystal comprising the steps of:

• electrically shorting the crystal;
• neutralizing space charge fields by heating the electrically shorted crystal;
• generating a metastable electronic space charge hologram by exposing the crystal to light in a selected pattern while maintaining the crystal electrically shorted;
• replicating the created metastable hologram in the form of a distributed ionic space charge pattern by heating the crystal while maintaining it electrically shorted;
• and
• illuminating the crystal with uniform high intensity electromagnetic wave energy while maintaining the crystal open circuited to erase the metastable hologram and leave only an optically readable ionic space charge pattern.

The method of converting metastable gratings in a photorefractive medium to substantially permanent gratings comprising the steps of:

• generating at least one electron charge grating in a medium having a geometry and dopant concentration and with electrical characteristics such that the limiting electronic space charge field E.sub.q is comparable to the diffusion field E.sub.d ;
• fixing an ionic charge grating in the medium by heating the medium to a thermal state of ion mobility;
• and
• developing the at least one grating by illuminating the medium with electromagnetic wave energy while maintaining E.sub.q comparable to E.sub.d.

A method for generating permanent ionic gratings in a photorefractive material by the steps of:

• generating at least one hologram in a reflection mode geometry by writing the hologram at an elevated fixing temperature while the crystal is short circuited to simultaneously create an electron charge pattern and compensating ionic pattern;
• cooling the material down to below the fixing temperature;
• and
• developing the at least one hologram by illuminating the medium with electromagnetic wave energy while maintaining E.sub.q comparable to E.sub.d.

The method of forming an enhanced holographic image in a crystal which is photorefractively sensitive to electromagnetic wave energy in a predetermined range, comprising:

• generating an electric field variation E.sub.1 in the crystal by illuminating the crystal with beams of electromagnetic waves to form an interference pattern in the crystal;
• concurrently maintaining the crystal in an electrically shorted state;
• inducing maximum photovoltaic current in the crystal;
• and migrating electrons within the crystal to trapping positions within the crystal until a space charge field is defined in accordance with the photorefractive property of the crystal.

The method of recording a holographic image in a photorefractive crystal comprising the steps of:

• establishing steady state electric field potentials across the crystal;
• generating an optical interference pattern within the crystal in the photorefractivity sensitivity band of the crystal to incident light,
• establishing E.sub.q approximately equal to E.sub.d, wherein E.sub.q is a limiting space charge field and E.sub.d is a diffusion field at ambient temperature, and
• redistributing photoexcited electrons within the crystal until a space charge field is established.