Intersubband absorption dynamics in coupled quantum wells

We apply an interband pump/intersubband probe technique to monitor the temporal evolution of the electron population in the first and second subband of an undoped GaAs/AlGaAs asymmetric double quantum well after interband optical excitation. The spacing between the two subbands is smaller than the longitudinal optical phonon energy. The time dependence of the intersubband absorption can be explained by a simple rate equation model. We extract an intersubband lifetime of T-21=100 ps and a recombination time of tau =410 ps at an excitation density of n(S)=2x10(11) cm(-2). (C) 2001 American Institute of Physics.