TIME-RESOLVED STUDIES OF EXCITONIC POLARITONS

The kinetic properties of the secondary emission of excitonic polaritons are reviewed, based on experiments on molecular (anthracene) and semiconductor (CdS, GaAs, InP, etc.) crystals at low temperatures. First, coherent propagation effects are considered, including group velocity renormalization, the appearance of optical precursors and photon echo type responses. Second, the problem of the radiative lifetime of polaritons is addressed, elucidating the appearance of gigantic oscillator strengths and the light (polariton) trapping phenomenon. Third, the kinetic characteristics of the luminescence spectrum are discussed with the emphasis on polariton relaxation, propagation, the distinction between Raman scattering and luminescence. Fourth, time-resolved reflection experiments are explained in the polariton framework.