We have developed a compact closed-form solution of the band transport model for high-contrast gratings in photogalvanic crystals. Our solution predicts the effect of the photoconductivity and the electric field grating enhancement due to the photogalvanic effect. We predict a pronounced dependence of the steady-state photogalvanic current on the contrast of the interference pattern and an increase of holographic storage time due to the enhancement of the photoconductivity grating contrast. In the high contrast limit and a large photogalvanic effect the refractive index grating will be shifted from the position of the intensity modulation pattern, contrary to the usually adopted model of unshifted gratings.
We present experimental results on the photorefractive two-beam coupling constant and response time of two Cr-doped strontium barium niobate crystals with different dopant concentrations. Both showed significantly faster response times over Ce-doped SBN:60, but with corresponding decreases in their coupling constants.
A new approach to holographic storage that uses lensless phase-conjugate holograms is proposed and demonstrated. Near-field holography is used for data recording, and a phase-conjugate reference beam is used for data retrieval. The data array can be directly transferred from the storage medium to the sensor without the need for imaging optics. It is shown that large space -bandwidth product holographic images (N x N x 10(6)) with pixel sizes of a few micrometers are feasible with a reasonable-sized recording material.
We present the results of experimental study of the absorption coefficient, two-beam photorefractive coupling constant, and photorefractive response time of a doubly Ce- and Ca-doped Sr0.6Ba0.4Nb2O6. This crystal displays enhanced photorefractive response at near infrared wavelengths when compared to Ce-doped SBN:60. The temperature dependence of the coupling constant over the range from −30 to 40 °C has also been studied.
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