  We investigate temperature-dependent resonance fluorescence spectra obtained
from a single self-assembled quantum dot. A decrease of the Mollow triplet
sideband splitting is observed with increasing temperature, an effect we
attribute to a phonon-induced renormalisation of the driven dot Rabi frequency.
We also present first evidence for a non-perturbative regime of phonon
coupling, in which the expected linear increase in sideband linewidth as a
function of temperature is cancelled by the corresponding reduction in Rabi
frequency. These results indicate that dephasing in semiconductor quantum dots
may be less sensitive to changes in temperature than expected from a standard
weak-coupling analysis of phonon effects.
