Coherent reflected pulses of exciton polaritons in multiple quantum wells at Brewster’s-angle incidence

A coherent emission of excitons in semiconductor multiple quantum wells was investigated by using transient Brewster reflection spectroscopy. The method reduced nonresonant background reflection greatly and allowed us to observe the coherent dynamics of the excitons clearly. The coherent signal showed not only the quantum beats of the heavy- and light-hole excitons but also the oscillatory modulation structures that resulted from the radiative coupling of exciton polaritons. In the linear regime, these observations were compared with results calculated from the transfer-matrix method involving multiple-reflection effects, and good agreement was obtained. As the excitation density of the incident pulses was raised, the decay rate of the coherent signal increased due to the exciton-exciton scattering.