We demonstrate ultrafast emph{incoherent} depopulation of a quantum dot from above to below the transparency point using LA-phonon-assisted emission stimulated by a red-shifted laser pulse. The QD is turned from a weakly vibronic system into a strongly vibronic one by laser driving which enables the phonon-assisted relaxation between the excitonic components of two dressed states. The depopulation is achieved within a laser pulse-width-limited time of 20~ps and exhibits a broad tuning range of a few meV. Our experimental results are well reproduced by path-integral calculations.
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