Angle-resonant stimulated polariton amplifier

We experimentally demonstrate resonant coupling between photons and exciton s in microcavities which can efficiently generate enormous single-pass opti cal gains approaching 100. This new parametric phenomenon appears as a shar p angular resonance of the incoming pump beam, at which the moving excitoni c polaritons undergo very large changes in momentum. Ultrafast stimulated s cattering is clearly identified from the exponential dependence on pump int ensity. This device utilizes boson amplification induced by stimulated ener gy relaxation.