Coherent response of a quantum dot exciton driven by a rectangular spectrum optical pulse

We observe strong nonlinear absorption in the excitation profile of a single InGaAs quantum dot exciton driven by a rectangular spectrum optical pulse, in a region of detuning where the linear response is weak. Here the exciton is resonant with the temporal side-lobes of the pulse, which drive a damped Rabi oscillation. Good agreement is found between experiment and a two-level atom model. In the nonlinear regime the excitation profile exhibits features from both the rectangular spectrum and the two peaks present in the spectrum of the autocorrelation of the pulse.