Polarization conversion from diffraction gratings made of uniaxial crystals

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Abstract
We study polarization conversion in the diffraction of light at the periodically corrugated boundary between an isotropic medium and a uniaxial crystal. To do so, we extend a rigorous method originally developed for diffraction gratings made of isotropic materials to include the case of anisotropic media. The theoretical formalism relies upon the use of easy coordinate transformations that map the periodic interface onto a plane. We consider a general configuration in which the incident beam is associated to waves coming either from the isotropic or from the uniaxial side, with any orientation with respect to the grooves of the grating for the plane of incidence (conical diffraction) and for the optical axis of the crystal. The analysis involves no restrictions on the surface relief profile. We apply the method to study conversion between polarization states upon reflection in two situations: (i) incidences from an isotropic, lossless dielectric onto a crystal near total reflection and (ii) from a crystal onto a metal near the resonant excitation of surface plasmons. Good results have been obtained for a groove height-to-period ratio up to 1. © 1996 The American Physical Society.