Beam shifts on reflection of electromagnetic radiation off anisotropic crystals at optic phonon frequencies

We discuss possible beam shifts on external reflection of electromagnetic radiation off an anisotropic crystal around its optic phonon frequencies. In certain situations, these displacements may oppose the energy flow within the crystal. We show examples for reflection off crystal quartz in various configurations. Displacements of the order of a wavelength should occur with significant reflected intensity. (paper)