High-temperature ultrafast polariton parametric amplification in semiconductor microcavities

Cavity polaritons, the elementary optical excitations of semiconductor micr ocavities, may be understood as a superposition of excitons and cavity phot ons(1). Owing to their composite nature, these bosonic particles have a dis tinct optical response, at the same time very fast and highly nonlinear. Ve ry efficient light amplification due to polariton-polariton parametric scat tering has recently been reported in semiconductor microcavities at liquid- helium temperatures(2-11). Here we demonstrate polariton parametric amplifi cation up to 120 K in GaAlAs-based microcavities and up to 220 K in CdTe-ba sed microcavities. We show that the cut-off temperature for the amplificati on is ultimately determined by the binding energy of the exciton. A 5-mum-t hick planar microcavity can amplify a weak light pulse more than 5,000 time s. The effective gain coefficient of an equivalent homogeneous medium would be 10(7) cm(-1). The subpicosecond duration and high efficiency of the amp lification could be exploited for high-repetition all-optical microscopic s witches and amplifiers. 10(5) polaritons occupy the same quantum state duri ng the amplification, realizing a dynamical condensate of strongly interact ing bosons which can be studied at high temperature.