  We predict a complete TM-TE transformation of the polarization of terahertz
electromagnetic waves reflected from a strongly anisotropic boundary of a
layered superconductor. We consider the case when the wave is incident on the
superconductor from a dielectric prism separated from the sample by a thin
vacuum gap. The physical origin of the predicted phenomenon is similar to the
Wood anomalies known in optics, and is related to the resonance excitation of
the oblique surface waves. We also discuss the dispersion relation for these
waves, propagating along the boundary of the superconductor at some angle with
respect to the anisotropy axis, as well as their excitation by the
attenuated-total-reflection method.
