Photorefractive (PR) effect is a light-induced change in the refractive index that involves photogenerated charge redistribution. The main mechanisms involved in the PR effect are space-charge field build-up, caused by photogeneration, transport and trapping of charge carriers, and refractive index change in the electric field due to anisotropic polar molecules reorienting in the electric field. The distinct feature of the PR effect is that the light-intensity pattern and a refractive-index patterns are phase-shifted with respect to each other, which results in an asymmetric energy transfer between two light beams, called two-beam coupling effect, utilized in numerous applications. Experimental geometries utilized in characterization of PR materials and in applications are two-beam coupling and four-wave mixing. In terms of PR organic materials design, most successful materials classes include polymer composites, amorphous glasses, fully functionalized polymers, and polymer-dispersed liquid crystals. Applications demonstrated in high-performance PR organic materials include data storage, image processing, optical limiting, switching, optical wave guiding, and many others.

In summary, the complexity of the PR effect in organic materials is fascinating, since a variety of physical processes contribute to the PR performance. The need to optimize all these processes represents a challenge in the material design. Nevertheless, over the past years, tremendous progress in both physical understanding of the PR effect in organics and in the development of high-performance materials has occurred, and many applications of PR organic materials have been demonstrated. The field of PR organic materials keeps evolving, and emergence of novel, improved materials will undoubtedly enable new exciting applications.

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