  An array of $N$ closely spaced dipole coupled quantum emitters exhibits
super- and subradiance with characteristic tailorable spatial radiation
patterns. Optimizing their geometry and distance with respect to the spatial
profile of a near resonant optical cavity mode allows to increase the ratio
between light scattering into the cavity mode and free space by several orders
of magnitude. This leads to a distinct nonlinear particle number scaling of the
relative strength of coherent light-matter interactions versus decay. In
particular, for subradiant states the collective cooperativity increases much
faster than the typical linear $\propto N$ scaling of independent emitters.
This extraordinary collective enhancement is manifested both in the intensity
and phase profile of the sharp collective emitter antiresonances detectable at
the cavity output port via transmission spectroscopy.
