Ultrafast spectroscopy of carriers and excitons in semiconductor microcavities

Experiments probing both the linear and nonlinear response of strongly coupled GaAs/AlGaAs microcavities using femtosecond spectroscopy are described. Vacuum-Rabi oscillations are observed following resonant coherent impulsive excitation, with a decay time equal to twice the cavity lifetime as expected. Off-resonant excitation results in a long (approximate to 600 ps) decay, resulting from the slow scattering of excitons into k approximate to 0 states, and thermalized luminescence, In the nonlinear response, a dynamic reduction in the normal-mode splitting is observed. In nonresonant excitation, this is followed by gain-switched lasing.