Abstract
We study the coherent response of an optically dense exciton system in GaAs quantum wells (QWs). For this, we resonantly excite $1s$ heavy-hole excitons in the QWs at 8 K with subpicosecond laser pulses. The excitonic polarization is probed using time integrated (TI) degenerate four wave mixing (DFWM) measurements in self-diffraction geometry. The average power density ${(I}_{1})$ of the leading laser pulse is systematically increased to large values, keeping that of the delayed pulse small and fixed. The dephasing rate of the excitonic coherent polarization (determined by the rate of decrease of the TI-DFWM signal with delay between the exciting pulses) attains saturation at large ${I}_{1}$ after an initial rise at small ${I}_{1}.$ In comparison, the coherent polarization (as given by the DFWM signal at a fixed delay) increases initially with ${I}_{1},$ reaches a peak and then decreases at large ${I}_{1}.$
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