Femtosecond dynamics of resonantly excited excitons in room temperature GaAs quantum wells.

We use tunable optical pulses of 150 fs duration to measure the dynamics of exciton absorption in optically excited room temperature GaAs/AlGaAs multiple quantum well structures. We observe a prompt efficient bleaching of the exciton peak and a partial recovery of that bleaching in 300 fs. We interpret this recovery in terms of ionization of the excitons by optical phonons.