Coherent exciton-polaritons modified by population dynamics and strong coupling

The exciton-polariton response in a monolithic semiconductor microcavity containing an InGaAs quantum-well is explored with 3-pulse multidimensional coherent spectroscopy (MDCS). Rephasing spectra are measured at three values of detuning between the exciton and cavity modes as a function of the population (mixing) time delay between the second and third pulses. Changes in the complex 2D spectrum with population time probe various interactions typically attributed to population dynamics. Our results show commonly seen Raman coherent contributions and energy transfer from the upper- to lower-polariton. Additionally, a change in amplitude and spectral phase shift associated with the lower and upper exciton-polaritons have been observed. Previous studies of population time dependence of excitons in a GaAs quantum well revealed persistent many-body effects arising due to polarization-polarization scattering between photoexcited bright states within the light-cone and dark states outside the light-cone. Finally, the spectral phase shift is also correlated with a slight change in the peak separation of the two polariton branches (at a single detuning), which would indicate that polarization-polarization scattering may affect the strength of the vacuum Rabi splitting.