Photorefractive BaTiO3 Crystal Research Articles

Model for mutually pumped phase conjugation

A model is proposed and demonstrated for mutually pumped phase conjugation when two mutually incoherent laser beams pump each other, producing a pair of phase-conjugate beams through a cross-readout process. The model considers the buildup of two independent counterpropagating oscillations in a ring resonator containing two-beam-cbupling gain media. The experimental demonstration of the model using two photorefractive BaTiO3 crystals in a ring cavity gave simultaneous phase-conjugate images with good fidelity and no image cross talk. As expected, the counterpropagating oscillations were slightly detuned in frequency (∼1 Hz) from the corresponding pumping beams with frequency shifts related to the ring-cavity length. Frequency shifts were also observed in the phase-conjugate beams, with their magnitudes dictated by energy conservation for nondegenerate four-wave mixing.

Digital optical processing with photorefractive materials: Applications of a parallel half-adder circuit to algorithmic state machines

Theoretical and experimental results are presented for a real-time parallel half-adder circuit with the use of nonlinear interactions in photorefractive media. The two-valued intensity input bit planes contain 256 bits in a 16×16 format. They are processed in parallel by three photorefractive BaTiO3 crystals operating in a two-wave mixing configuration. Sequential algorithms for binary arithmetic can be implemented by providing the processor with a feedback loop. A prototype photorefractive algorithmic state machine that performs multibit operations between two arrays of numbers is proposed. The addition of two sequences of 5-bit numbers is experimentally demonstrated, and improved performances are expected with the use of phase conjugation techniques.

Self Bragg matched beam steering using the double color pumped photorefractive oscillator

A new method for steering light beams with automatic (self-aligning) Bragg matching is presented. This device enables, in principle, a large beam deflection range which is not limited by the Bragg condition. It is based on a double color pumped photorefractive oscillator. Two input beams of different colors induce and pump a dynamic four-wave mixing process in a photorefractive BaTiO3 crystal in which two other beams and a common grating are self-generated. Steering is achieved by wavelength tuning of one of the pump beams. A deflection range of about 1.7°, with an efficiency ranging from 50 to 90%, is measured for a wavelength difference Δλ of ±30 nm for the two pumps (using argon ion laser lines). A deflection of 4.7° with an efficiency of 10% is seen for Δλ=144.8 nm (corresponding to pumps at 488 and 632.8 nm).

Beam coupling in photorefractive BaTiO_3 crystals

Beam-coupling experiments are carried out with two BaTiO(3) crystals as a function of the intensity and wavelength. We demonstrate in these experiments that hole-electron competition is not the only mechanism responsible for the anomalous behavior of photorefractive BaTiO(3) crystals. We find that the intensity-dependent absorption coefficient plays a major role in beam-coupling experiments.