1. Physics Department, Swiss Federal Institute of Technology Lausanne, PH-Ecublens, CH-1015 Lausanne-EPFL, Switzerland
2. Centre National de la Recherche Scientifique, L2M-CNRS, 92225 Bagneux Cedex, France
3. Laboratoire de Spectrometrie Physique, Université J. Fourier-Grenoble, F-38402 Saint Martin d'Hères Cedex, France
4. Dipartimento di Fisica and Istituto Nazionale di Fisica della Materia, Università degli Studi di Cagliari, I-09042 Monserrato, Italy

Correspondence to: M. Saba¹ Correspondence and requests for materials should be addressed to M.S. (e-mail: Email: Michele.Saba@epfl.ch).

Abstract

Cavity polaritons, the elementary optical excitations of semiconductor microcavities, may be understood as a superposition of excitons and cavity photons¹. Owing to their composite nature, these bosonic particles have a distinct optical response, at the same time very fast and highly nonlinear. Very efficient light amplification due to polariton–polariton parametric scattering has recently been reported in semiconductor microcavities at liquid-helium temperatures^{2, 3, 4, 5, 6, 7, 8, 9, 10, 11}. Here we demonstrate polariton parametric amplification up to 120 K in GaAlAs-based microcavities and up to 220 K in CdTe-based microcavities. We show that the cut-off temperature for the amplification is ultimately determined by the binding energy of the exciton. A 5-m-thick planar microcavity can amplify a weak light pulse more than 5,000 times. The effective gain coefficient of an equivalent homogeneous medium would be 10⁷ cm^-1. The subpicosecond duration and high efficiency of the amplification could be exploited for high-repetition all-optical microscopic switches and amplifiers. 10⁵ polaritons occupy the same quantum state during the amplification, realizing a dynamical condensate of strongly interacting bosons which can be studied at high temperature.