Ultrafast polariton relaxation dynamics in an organic semiconductor microcavity

We study an organic semiconductor microcavity operating in the strong-coupling regime using fs pump-probe spectroscopy. By probing the induced absorption associated with the one-exciton to two-exciton transition, we are able to characterize the time-dependent population densities of states in the upper- and lower-polariton branches following impulsive excitation. We model the time-dependent polariton dynamics and provide direct evidence of a scattering process that returns upper-branch cavity polaritons to states in the exciton reservoir having a rate of (150 fs)^-1. A slower process similarly populates lower-branch polaritons by return scattering from the exciton reservoir.