Damping dispersion of excitonic polaritons in CdS

We extract the damping dispersion {Γ}({ω}) of excitonic polaritons in CdS on the basis of precise measurements of the transmission and reflectance. On the low-energy side of the Aₙ₌₁ exciton, the damping, which corresponds to the inverse dipole dephasing time, is independent of temperature, due to the scattering with impurities. On the high-energy side the damping increases with temperature and with the detuning from the resonance frequency due to the scattering with acoustic-phonons between different polariton modes. The probability of exciton-phonon scattering mediated by the deformation potential and by the piezoelectric effect is calculated and the measured damping spectrum is described qualitatively and quantitatively. By analyzing our results different relaxation channels of acoustic-phonon scattering are clearly discriminated.