Angle-dependent polariton collisional broadening in semiconductor microcavities

The polariton nonlinear dynamics in a II–VI semiconductor microcavity has been studied using angle-resolved four-wave mixing. The low-energy polariton dephasing time is found to decrease at large angles, when polariton can escape towards the excitonic reservoir, in good agreement with a calculation of the angle-dependent collisional broadening. Moreover, we find that the parametric amplification of k=0 polaritons is associated to a strong quenching of the coherence at the magic angle.