Abstract

We use time-resolved differential transmission spectroscopy with time resolution better than 100 fs to determine the intersubband relaxation of optically excited electrons in GaAs/AlGaAs quantum wells. We perform pump-probe measurements by using near-infrared pump pulses tunable from 1.44 to 1.56 eV and a white-light continuum probe. Pump-induced transmission changes are recorded as differential-transmission spectra (DTS). For quantum wells, these spectra mainly show excitonic absorption saturation at the various excitonic transitions because of carrier-induced loss of excifon oscillator strength and exciton broadening. It has been shown previously that the former effect can be separated from pure broadening by integrating the DTS over the width of the broadened exciton line. This integrated transmission change is directly related to the population of the subbands that contribute to the exciton under consideration. It is, however, not sensitive to intrasubband carrier relaxation.¹

© 1994 Optical Society of America