  We explore the generation of anti-Stokes fluorescence from strongly coupled
organic dye microcavities following resonant ground-state excitation. We
observe polariton emission along the lower polariton branch, with our results
indicating that this process involves a return to the exciton reservoir and the
absorption of thermal energy from molecules in a vibrationally excited
ground-state. We speculate that the generation of a population of "hot"
polaritons is enhanced by the fact that the cavity supresses the emission of
Stokes-shifted fluorescence, as it is located energetically below the cut-off
frequency of the cavity.
