We have studied the dynamics of the light emitted by a semiconductor microcavity paying special attention to the time-evolution of the degree of polarization, P of the photoluminescence. P depends strongly on the excitation power-density, an abrupt increase occurs when the emission becomes stimulated. Furthermore. we have found that a finite time is needed to reach the highest value of spin orientation. in contrast with the case of excitons in quantum wells where the spins are aligned almost instantly after a pulsed excitation. The faster emission dynamics of the polaritons that undergo stimulated emission, as compared with that of the polaritons with opposite spin, produces a very fast and efficient reversal of the polarization in the nonlinear regime. (C) 2001 Elsevier Science Ltd. All rights reserved. References: 92
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