Photorefractive processes

Autowave light scattering

One of the most interesting specific kinds of photoinduced light scattering is autowave scattering. If we use a steady laser radiation as an exciting light, all the processes of photoinduced light scattering are also at least quasi stationary. The scattering intensity could smoothly vary, in some time it reaches a saturation value and then remains invariable. This is right for all known kinds of photoinduced light scattering except one strange kind named autowave scattering. This scattering essentially differs from the kinds of photoinduced light scattering. It is substantially non-stationary.

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Photoinduced dispersion

A situation similar to four wave cross scattering could be displayed if we use two ordinarily polarized pumping beams with different wave lengths (in our experiments – green and yellow components λ1=0.5106 μ, λ2=0.5782 μ of cupper laser radiation)

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Four wave cross scattering

The real samples used in holographic experiments have limited dimensions and usually are enough transparent so that there always exists reflection by rear side of the crystal.

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Photoinduced light scattering

In a word, photorefractive phenomenon is a change of medium refractive index under action of electromagnetic radiation of light range. Of course refractive index could change in nonlinear optics. But photorefractive effect is not a nonlinear-optical one. First, photorefractive effect does not demand presence of strong light excitation. Just comparatively weak light radiation (with intensity about some mW per square cm) can induce significant (at least observable) change of refractive index of a medium (some units multiplied by ten in minus third or fourth power) (third or fourth digit after point). Secondly, photorefractive changes do not occur instantly and can be observed in some time (seconds, minutes) after switching on light illumination.

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