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The photorefractive effect
Support: EU (INTAS), Danish Government
The study of dynamic holograms recorded in photorefractive materials has uncovered a wealth of interesting physics and potential applications, including image amplification and correlation, phase conjugation and optical neural computing. Unlike nonlinear optics making use of the nonlinear polarisation, the 'strength' of the photorefractive effect does not depend on the incident optical intensity, which opens up the possibility of nonlinear optical signal processing using cheap, low power semiconductor diode lasers. Recent work has concentrated on using a novel experimental geometry to study the origin of sub-harmonic gratings that arise during two-wave mixing. We have proven that these gratings are a result of non-linearity in the material equations and do not require beam coupling. A consequence is that these subharmonic gratings may be present in materials that do not exhibit the linear electro-optic effect and which are therefore not photorefractive.
Relevant publications:
1. H. C. Pedersen, P. M. Johansen, and D. J. Webb, "Photorefractive
subharmonics -a beam-coupling effect," accepted for publication in J.
Opt. Soc. Am. B (1997).
2. H. C. Pedersen, D. J. Webb, and P. M. Johansen, "Influence of
beam-coupling on photorefractive parametric oscillation in a DC field
biased Bi12SiO20 crystal," submitted to J. Opt. Soc. Am. B (1997).
3. H. C. Pedersen, D. J. Webb, E. V. Podivilov, P. M. Johansen, B. I.
Sturman, and K. H. Ringhofer, "Resonance-instability of running
gratings in sillenite crystals," submitted to Phys. Rev. Lett. (1998).
Staff Involved:
Dr. D.J.Webb
Dr. H.K. Pedersen