Spatial light modulation by beam coupling in GaAs crystals

Hot-carrier enhancement of photorefractive space-charge fields in zinc-blende semiconductors

We observe an order-of-magnitude enhancement of the photorefractive effect in undoped CdTe on ~1-ps time scales that is caused by an overshoot in the two-photon-produced Dember space-charge field associated with hot-carrier transport.

Photorefractive nonlinearities caused by the Dember space-charge field in undoped CdTe

The photorefractive nonlinearity associated with the Dember space-charge field between electrons and holes produced by two-photon absorption is unambiguously isolated and studied in undoped CdTe by using a nondegenerate, forward-probing, polarization-sensitive, transient-grating technique with a temporal resolution of <5 ps.

Picosecond separation and measurement of coexisting photorefractive, bound-electronic, and free-carrier grating dynamics in GaAs

A novel transient-grating geometry, which is nondegenerate, copropagating, phase matched, and polarization sensitive, is used to isolate and measure independently the ultrafast dynamics of multiple coexisting gratings in GaAs:EL2 with a temporal resolution of <5 psec. This technique permits the measurement of the evolution of the photorefractive grating in materials with zinc blende symmetry, where the photorefractive grating is usually obscured by the stronger free-carrier and instantaneous bound-electronic gratings.

Matrix-vector multiplication in thin photorefractive GaAs crystals

Optical matrix-vector multiplication using four-wave mixing in a thin photorefractive GaAs crystal is demonstrated. Using a thin wafer of GaAs offers the potential to integrate the encoding spatial light modulators directly on the wave-mixing medium.

Optical correlators with fast updating speed using photorefractive semiconductor materials

An updatable optical correlator which uses a photorefractive compound semiconductor to generate real-time matched filters is proposed. Using compound semiconductors offers high speed with low optical input intensities. Here we discuss issues affecting the performance of this correlator. This includes an analysis of the Bragg diffraction and a discussion of the speed and power considerations of these materials. Experimental results obtained using photorefractive GaAs are also presented.

Index grating lifetime in photorefractive GaAs

The index grating lifetime in liquid encapsulated Czochralski-grown undoped semi-insulating GaAs was measured using a beam coupling technique. The largest lifetime measured was ~8 s under a read beam intensity of 0.7 mW/cm(2) with the grating periodicity being 0.63 microm. The measured value decreases to milliseconds as the read beam intensity and the grating periodicity increase to ~10 mW/cm(2) and 4 microm, respectively. This range of grating lifetime in this material is adequate for its use in real-time spatial light modulators, reconfigurable beam steering devices, and dynamic memory elements for optical computing. In addition, the results suggest that, the lifetime is sensitive to residual imperfections in the crystal.

Cross-polarization beam coupling in photorefractive GaAs crystals

We report theoretical and experimental investigations on the cross-polarization coupling of two contradirectional laser beams in a photorefractive GaAs crystal. There is good agreement between these results.