Multiple grating formation in photorefractive polymers with azo-dye chromophores

Photorefractive polymers which incorporate azo-dyes as the nonlinear chromophore element, can be used not only for generating gratings by the photorefractive effect, but also by photoisomerization of the azo-dye. In the latter mechanism, repeated trans-cis isomerization causes the chromophore molecules to become aligned at right angles to the laser polarization direction, thereby making the material birefringent. These two phenomena are to a large degree independent, and can be studied separately, by appropriate choice of polarization direction of the interacting beams. Furthermore, the diffraction efficiency of the photorefractive gratings is a very sensitive function of the poling field strength, while that of the photoisomerization gratings is less so. In this work, we investigate the components diffracted from each of these gratings formed in a hybrid photorefractive polymer material PVK:TNF:DEACST:disperse red 1. We then explore the possibility of performing some simple optical processing applications, exploiting the flexibility provided by this multiple grating process. A scheme for producing a novelty filter, which displays only the moving parts of a scene is considered. The limitations of these films for such processing applications are discussed.