Excitonic ac Stark splitting in quantum wells

The evolution of the absorption spectrum of a specially designed single In0.04Ga0.97As quantum well as a function of the growing excitation density was reported. The excitation is provided by a pulsed Ti:sapphire laser and the measurements are taken in a pump-probe geometry. The pump pulses is spectrally filtered and selectively excite the exciton line, thus reducing the creation of free electron-hole pairs; the probe pulses are instead left broadband in order to detect the whole spectrum at the same time. Results show that the two dispersive Stark sidebands, which, for growing pump intensities, shift from the exciton line towards low and high energies.