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Low-scattering and highly efficient orientational gratings are obtained, exploiting polarization holography to modulate the in-plane anchoring axis at both surfaces of a planar nematic cell. Polarization-sensitive azo-dye-doped polyimide films are used as aligning layers. For proper values of cell thickness and spatial periodicity of the gratings, the director configuration in the nematic bulk is a perfect replica of the polarization gratings recorded on the aligning layers. High first-order diffraction efficiency, up to 98%, is observed in thin grating regime. External ac voltage allows to adjust the efficiency over the whole range for arbitrary cell thickness.
Provenzano et al. (Mon,) studied this question.