Femtosecond time‐resolved free‐induction decay of room‐temperature excitons in GaAs quantum wells

We directly resolve the femtosecond free‐induction decay of excitons in GaAs quantum wells at room temperature by upconverting the diffracted signal from a transient four‐wave‐mixing experiment. At high laser intensities, we find significant deviations from the temporal evolution of the time‐integrated and peak amplitude signals, which we attribute to many‐body Coulomb effects.