Dispersionless polaritons at symmetrically oriented surfaces of biaxial crystals

A set of dispersion relations is derived for surface polaritons in optically biaxial crystals at the surfaces parallel to the symmetry planes of the permittivity tensor epsilon. The domains of existence, as well as the sectors of the propagation directions of dispersionless surface polaritons which arise at positive components of the tensor epsilon, are analyzed. Three nonoverlapping domains of the dielectric-anisotropy parameters where dispersionless polaritons can exist are found for weakly anisotropic crystals. In each of these domains, polaritons exist at two different mutually orthogonal surfaces of the crystal. In optically biaxial crystals, in contrast to optically uniaxial media, polaritons arise not only in positive but also in negative crystals. The evolution of the optical-axis configuration is traced as the anisotropy parameters vary in the domains of existence of polaritons. (C) 2002 MAIK Nauka/Interperiodica.