COHERENT REFLECTED PULSES OF EXCITON POLARITONS IN MULTIPLE-QUANTUM WELLS AT BREWSTERS-ANGLE INCIDENCE

A coherent emission of excitons in semiconductor multiple quantum well s was investigated by using transient Brewster reflection spectroscopy . The method reduced nonresonant background reflection greatly and all owed us to observe the coherent dynamics of the excitons clearly. The coherent signal showed not only the quantum beats of the heavy-and lig ht-hole excitons but also the oscillatory modulation structures that r esulted from the radiative coupling of exciton polaritons. In the line ar regime, these observations were compared with results calculated fr om the transfer-matrix method involving multiple-reflection effects, a nd good agreement was obtained. As the excitation density of the incid ent pulses was raised, the decay rate of the coherent signal increased due to the exciton-exciton scattering.