Exciton-Polariton Dispersion of Alkali Bromides Observed with Interference Method

The dispersion of exciton-polaritons in RbBr has been studied in the vicinities of the halogen-doublet Γ(3/2,1/2) and Γ(1/2,1/2) exciton resonances by using an interference method. The results are combined with the data of the upper branch of the Γ(3/2,1/2) exciton-polariton obtained by Fröhlich's group, and are analyzed with use of the dispersion formula based on a two-oscillator model. The analysis yields fundamental exciton parameters for each of the halogen-doublet states, such as the transverse resonance energy, the longitudinal-transverse splitting and the background dielectric constant. From these values, the oscillator strength and the analytic exchange energy are also deduced for the excitons in RbBr.