Time-resolved excitonic coherent polarization dynamics in GaAs multiple quantum wells

We investigate pump induced modulation in the temporal evolution of the excitonic coherent polarization generated by a probe pulse in GaAs multiple quantum wells. For this, we perform femtosecond time resolved (TR) pump-probe differential reflectivity (PPDR) measurements using frequency upconversion at both positive and negative pump-probe delays. Comparison of the data with a theoretical model highlights the importance of the contribution arising from interference of excitonic linear and nonlinear polarizations for understanding the TR-PPDR measurements.