Photorefraction birefringent materials

Electro-Optic and Electric-Field-Induced Birefringent Materials. As can be seen from the analysis of The Photorefractive Process section, one material parameter to be optimized is the electro-optic and orientational response. This can be accomplished either by finding compatible materials with large linear electro-optic coefficients or by optimizing the orientational effects using materials with large birefringence (polarization anisotropy). One major difference in these approaches is the response speed of the photorefractive effect in that the orientational approach is expected to be slower, but submillisecond responses of low Tg materials have been demonstrated (93-96). 

As shown previously, nematic liquid crystals reorient easily in weak electric fields and their high birefringence provides an efficient electro-optic mechanism that makes them excellent candidates for photorefractive materials. However, charge transport relies on the generation of mobile anions or cations. These mobile charges obey the current density (/) equations given by [82,83]... 

The material has to simultaneously possess photoconductivity and electro-optical effect to have photorefractive properties. Typical candidate materials have low glass transition temperature, frequently reduced by the plasticizer. Diffraction efficiency is improved by addition of the plasticizer because chromophore groups have higher rotational mobility and increase their contribution of birefringence to the total refractive index modulation. ... 

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