The excitation of surface plasmons at a flat interface between a uniaxial crystal and a metal is investigated theoretically. We show that strong couplings between surface plasmons and light incident from the crystal can be obtained without corrugation of the surface. These couplings are associated with significant reductions in the reflectivity of the structure and with strong enhancements of the electromagnetic field on the surface of the crystal. Numerical examples obtained for a flat interface between sodium nitrate and gold show the existence of critical orientations of the optic axis for which all the incident power is absorbed by the metal.
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