DAMPING DISPERSION OF EXCITONIC POLARITONS IN CDS

We extract the damping dispersion GAMMA(omega) of excitonic polaritons in CdS on the basis of precise measurements of the transmission and r eflectance. On the low-energy side of the A(n=1) exciton, the damping, which corresponds to the inverse dipole dephasing time, is independen t of temperature, due to the scattering with impurities. On the high-e nergy side the damping increases with temperature and with the detunin g from the resonance frequency due to the scattering with acoustic-pho nons between different polariton modes. The probability of exciton-pho non scattering mediated by the deformation potential and by the piezoe lectric effect is calculated and the measured damping spectrum is desc ribed qualitatively and quantitatively. By analyzing our results diffe rent relaxation channels of acoustic-phonon scattering are clearly dis criminated.