EN
We report on cw optical experiments performed in a semiconductor microcavity containing a single quantum well in the strong coupling regime. Angularly resolved photoluminescence measurements under non-resonant excitation show the collapse of a relaxation bottleneck as the excitation power is increased. As a result, the emission close to k_{∥}=0 presents a non-linear behavior. In a two-beam experiment we resonantly inject polaritons at k_{∥}=0 and show that relaxation from states with large in-plane wave vector toward k_{∥}=0 is stimulated by the polariton final state population.