Microcavity polariton depopulation as evidence for stimulated scattering

We report on a c.w. two-beam experiment unambiguously evidencing the polariton transfer from initial states to final states which takes place through a stimulated scattering process. One beam is nonresonant while the other resonantly creates a large occupation factor in the lower polariton final state. Gain, resulting in a deepening of the lower polariton reflectivity dip, is observed on the resonant beam. Simultaneously, the luminescence of large in-plane wave-vector states decreases linearly with the resonant power.