Dispersion of Phonon‐Like Surface Polaritons on α‐Quartz Observed by Attenuated Total Reflection

The dispersion of ordinary and extraordinary phonon‐like surface polaritons on α‐quartz has been measured on two crystallographic faces parallel and perpendicular to the c‐axis in the frequency range 350 to 1200 cm −1 , covering all reststrahlen bands except the two lowest for polarization perpendicular to the optical axis. The method used was the attenuated total reflection method for transverse magnetic polarized radiation. The results are in very good agreement with theoretical calculations of the dispersion curves, using literature values for the freguencies of transverse and longitudinal optical phonons. Cut‐off wave vectors for so called “virtual excitation” surface polaritons are observed in agreement with theory.