Directional dispersion of polar phonons measured by infrared reflection

Abstract

AbstractThe dispersion of all polar optical phonons may be measured by the attenuated total reflection method. It is shown how the directional dispersion of the extraordinary polar phonons in uniaxial crystals is obtained in a similar way. In the (ω, k) diagram the areas of high reflectivity for transverse magnetic polarized incident radiation are determined by curves which have for k → 0 the same frequencies as extraordinary phonons propagating in an infinite crystal for k → ∞. At arbitrary crystal cuts these curves are boundaries for the existence of surface phonon‐polaritons. The method allows measuring the complete directional dispersion of t—t and l—l branches of Raman‐inactive polar phonons, too.