Résumé
The broadening of polariton lines by acoustic phonons is investigated in a semiconductor microcavity by means of interferometric correlation measurements with subpicosecond resolution. A decrease of the polariton-acoustic phonon coupling is clearly observed for the lower polariton branch as one approaches the resonance between exciton and photon states. This behavior cannot be explained in terms of a semiclassical linear dispersion theory but requires a full quantum description of the microcavity in the strong-coupling regime.