Two color picosecond time resolved PL studies of anti-Stokes PL in GaAs/AlGaAs asymmetric double quantum wells

We have performed two color, picosecond time-resolved PL experiments on the anti-Stokes PL (ASPL) in GaAs/AlGaAs ADQW at 10 K. By using independently tunable, synchronized picosecond Ti:sapphire laser system combined with a streak camera, we probe the time evolution of the ASPL from the narrow well when one picosecond laser excites the wide well (WW) only, and the other is tuned below the heavy hole exciton energy of the WW where it cannot create any carriers on its own. We have demonstrated that the forbidden two step absorption process has strong contribution to the ASPL in our ADQW samples. In addition, we found that the very long lived states play an important role in the two step absorption process of ASPL, which is invisible by other experimental methods.