The microcavity AC Stark triplet: Excitation in the exciton continuum

The coherent optical response of high quality microcavities containing quan tum wells is investigated. The dynamics of the ac Stark effect is investiga ted by degenerate pump-probe experiments, by exciting the quantum well exci tons at various intensities and detunings. The evolution from a simple dyna mical excitonic Stark shift to a splitting is dearly observed, even when th e excitation is degenerate with the continuum states. The experimental resu lts agree well with the predictions of a theoretical model based on the sem iconductor Maxwell-Bloch equations.