Seeding of polariton stimulation in a homogeneously broadened microcavity

In time-resolved light emission from a high-quality semiconductor microcavi ty after pulsed excitation suitable for angle-resonant polariton-polariton scattering on the lower-polariton branch, we find strong evidence for final -state stimulation of this process. The self-stimulated emission, following single-pulse excitation, appears on a fast time scale of only a few lens o f ps with a maximum at 15 ps. This is in striking contrast to the photolumi nescence decay time of 110 ps observed in the low-density limit. By injecti on of polaritons into the final state by a seeding pulse, the dynamics and the intensity of this emission can be controlled. The time-resolved data an d the density dependences are in agreement with a rate equation model negle cting polarization mixing effects. This model gives a coupling coefficient of b(LP,k)=0 = 2.4 x 10(-9) cm(4) s(-1) for the stimulated angle-resonant p olariton-polariton scattering process.