Femtosecond coherent control of absorption and free induction decay in a GaAs multiple quantum well

Excitonic polarizations are coherently excited using two phase-locked pulse s. By probing the linear propagation of the pulses through a GaAs/AlGaAs mu ltiple quantum well sample, we directly demonstrate the intriguing interact ion between the coherent exciton polarizations and the controlling pulses. It is shown that the second pulse can be either strongly amplified by takin g up energy gained from the destruction of the exciton polarization or dras tically decreased by giving up all its energy to excitons. The temporal sig natures of the transmitted pulse shapes agree well with model calculations.