Polariton-acoustic-phonon interaction in a semiconductor microcavity

The broadening of polariton lines by acoustic phonons is investigated in a semiconductor microcavity by means of interferometric correlation measureme nts with subpicosecond resolution. A decrease of the polariton-acoustic pho non coupling is clearly observed for the lower polariton branch as one appr oaches the resonance between exciton and photon states. This behavior canno t be explained in terms of a semiclassical linear dispersion theory but req uires a full quantum description of the microcavity in the strong-coupling regime.