Noise reduction in photorefractive image amplifiers and applications

We propose and experimentally demonstrate two original methods for suppressing the beam fanning noise of photorefractive amplifiers. The first one involves two wave mixing in a slowly rotating crystal, while the second requires to tilt the crystal with respect to the recording beams. This method applies to materials which exhibit a sharp resonance of the gain versus the pump-probe beam angle. With both methods a large improvement of the $S/N$ ratio is achieved and virtually noise free image amplifiers are demonstrated. In Bi$_{12}$SiO$_{20}$, subpicowatt optical signals are detected and amplified. By using combinations of LiNbO$_3$/Bi$_{12}$SiO$_{20}$, as storage and amplification crystals respectively a long term readout (more than 20 hours) of a photorefractive memory is achieved

Nonlinear transport in semiinsulating gaas - critical fields and nucleation of high-field domains

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