  We demonstrate ultrafast incoherent depopulation of a quantum dot from above
to below the transparency point using LA-phonon-assisted emission stimulated by
a redshifted 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.
