Threshold power and internal loss in the stimulated scattering of microcavity polaritons

Circularly polarized excitation (sigma(+)) and detection (sigma(+),sigma(-)) techniques are employed to demonstrate the role of internal losses in determining threshold powers and spectroscopic energies in the regime of stimulated polariton scattering. Very marked increases of linewidth with temperature and excitation intensity are found for the nonstimulated sigma(-) minority spin orientation, and provide a direct probe of the internal losses. The losses thus determined provide a very good explanation for the increases of threshold power and the blueshifts in signal and idler energies with temperature found for the stimulated sigma(+) emission. Good semiquantitative agreement with recent theories is found.