Spectral Emission by Polaritons in LiF

Abstract

The upper branch of the polariton dispersion curve has been experimentally obtained by measuring the thermal emission spectra of thin films of LiF at oblique emission angles. The formulation based on the virtual mode theory is given for determination of the dispersion relation. The dispersion curve has been obtained from the resonance frequency and width of the thermal emission due to 0 TH mode which is the lowest mode at higher frequency region than LO frequency.
Measurements have been performed at temperatures 420°K and 605°K and at emission angles ranging from 45° to 80°. The results agree fairly well with the theory.