  Using angle-resolved Raman spectroscopy, we show that a resonantly excited
ground-state exciton-polariton fluid behaves like a nonequilibrium coolant for
its host solid-state semiconductor microcavity. With this optical technique, we
obtain a detailed measurement of the thermal fluxes generated by the pumped
polaritons. We thus find a maximum cooling power for a cryostat temperature of
$50$K and below where optical cooling is usually suppressed, and we identify
the participation of an ultrafast cooling mechanism. We also show that the
nonequilibrium character of polaritons constitutes an unexpected resource: each
scattering event can remove more heat from the solid than would be normally
allowed using a thermal fluid with normal internal equilibration.
