  Scattering processes in an optical microcavity are investigated for the case
of silicon nanocrystals embedded in an ultra-high Q toroid microcavity. Using a
novel measurement technique based on the observable mode-splitting, we
demonstrate that light scattering is highly preferential: more than 99.8% of
the scattered photon flux is scattered into the original doubly-degenerate
cavity modes. The large capture efficiency is attributed to an increased
scattering rate into the cavity mode, due to the enhancement of the optical
density of states over the free space value and has the same origin as the
Purcell effect in spontaneous emission. The experimentally determined Purcell
factor amounts to 883.
