Giant angle-resonant polariton amplification

We discuss recent theoretical results on the polariton parametric amplifica tion from semiconductor microcavities in the strong exciton-photon coupling regime. A microscopic treatment of the interacting polariton system leads to a clear description of the phase-matched four-polariton mixing. The resu lts excellently explain the recent observation of giant angle-resonant ampl ification in pump-probe experiments with co-circularly polarized beams.