Dispersion of surface polaritons in uniaxial Al/sub 2/O/sub 3/

The dispersion of ordinary and extraordinary surface polaritons in uniaxial Al/sub 2/O/sub 3/ crystals has been measured with use of the attenuated-total-reflection method. Some additional reflectivity minima are observed, which are not associated with the excitation of surface polaritons, but are due to the low-reflectivity regions bounded by the optical-phonon-mode frequencies and the bulk-polariton dispersion curve. The discrepancies among the theoretical surface-polariton dispersion curves calculated with the use of various methods are discussed.