Monitoring the dynamics of a coherent cavity polariton population

We report on time-resolved photoluminescence measurements on a II-VI CdTe∕CdMnTe semiconductor microcavity in the strong-coupling regime. Under nonresonant excitation, we observe the buildup of a large population in the polariton states close to the Brillouin-zone center with occupation factors larger than 10. A spectacular spectral narrowing is measured, together with a strong acceleration of the polariton relaxation. A simple rate equation model describing the stimulated polariton-polariton scatterings toward the lowest-energy polariton states gives a good overall description of the measured dynamic.