Influence of nonstimulated polariton relaxation on parametric scattering of microcavity polaritons

摘要

Stimulated parametric scattering of polaritons has been investigated in a GaAs-based microcavity for varied depths of the lower polariton (LP) branch energy minimum with respect to the free exciton level. We find that despite overall growing losses in the polariton system, for the deep LP branch (with the band minimum > 3.3 meV below the exciton level) the threshold for stimulation W_(th) strongly decreases with temperature T. We show that for a deep LP branch the LP population arising from incoherent polariton relaxation at elevated T plays the role of an efficient "seed" for the highly coherent process of the polariton parametric scattering. The influence of efficient nonstimulated relaxation on W_(th) at low T is also confirmed in the experiments when additional laser excitation above the band gap of GaAs is used to enhance the polariton relaxation. Our observations indicate that in addition to the four-wave-mixing formalism describing only four waves participating in the parametric process, the full physical picture including other relaxation channels should be taken into account to reproduce the observed nonlinear behavior accurately.