Dynamics of the transition from strong to weak coupling regime in a system of exciton polaritons in semiconductor microcavities

The dynamics of polaritonic emission of a GaAs-based microcavity with embedded quantum wells under nonresonant optical excitation is studied. Kinetic dependences of the intensity, spectral position, and linewidth of spontaneous and stimulated emission of the microcavity are measured. It is established that the dynamics of the high-frequency shift of the emission line is qualitatively similar to the dynamics of the emission intensity, but the spectral shift attains its maximum value before the peak intensity is reached. The emission linewidth is maximal immediately after the excitation pulse. Under the conditions of spontaneous emission, the linewidth decreases steadily with time, approaching the value corresponding to low polariton densities. Under lasing conditions, the linewidth is at a minimum when the stimulated-emission intensity attains its peak value. The experimental data are analyzed on the basis of a theoretical model that describes relaxation processes taking into account exciton-exciton and exciton-free carrier interactions.