Small-Angle Oblique-Incidence Infrared Reflection in Polar Materials: I. Model Approach

概要

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Nearly normal off-axis infrared reflection due to polar optical phonons has been examined numerically for cubic and uniaxial crystals. Even at a small angle of incidence, Brewster’s law causes null reflection to the ρ-polarized light at frequencies just above LO modes, since the dielectric function monotonically increases from zero with increasing frequency above an LO mode. The total reflection due to Snell’s law may also take place in s- and ρ-polarizations. These effects give rise to steep minima and maxima, depending on the orientation and phonon structure of the crystal examined, in the reflection spectrum around LO modes. Although the structures are suppressed strongly by damping, they may become sufficiently intense to be experimentally observed in real bulk crystals if the angle of incidence is elevated up to approximately 10. On the basis of these findings, we propose that small-angle oblique-incidence reflectometry is a reliable method of characterizing optical phonons in polar materials.