Nonlinear Optics and Photonic Applications of Photorefractive Polymeric Composite Materials
Until very recently the photorefractive effect has been observed exclusively in inorganic crystals, such as BaTiO3, doped GaAs, BSO, and others. The organic polymeric photorefractive films define an entirely new and very promising class of media exhibiting photorefractive response. The crucial functions for photorefractivity are photoconductivity and electro-optic activity. Known inorganics show high X(2) nonlinearities and moderate to high carrier mobilities. However, there is an inherent limitation is imposed on the photorefractive figure of merit, n3reff/є (where n is the refractive index, reff the effective electro-optic coefficient, and є the material's dielectric constant), for these systems due to the ionic polarizability origin of their nonlinearities resulting in high values of є.1 Secondly, these materials are very difficult to fabricate and process. Organics differ from their inorganic counterparts in that they are easy to process and, due to the localized nature of their electronic properties, combine low dielectric constants and relatively high electro-optic coefficients.
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