  We investigate the collective optomechanics of an ensemble of scatterers
inside a Fabry-Perot resonator and identify an optimized configuration where
the ensemble is transmissive, in contrast with the usual reflective
optomechanics approach. In this configuration, the optomechanical coupling of a
specific collective mechanical mode can be several orders of magnitude larger
than the single-element case, and long-range interactions can be generated
between the different elements since light permeates throughout the array. This
new regime should realistically allow for achieving strong single-photon
optomechanical coupling with massive resonators, realizing hybrid quantum
interfaces, and exploiting collective long-range interactions in arrays of
atoms or mechanical oscillators.
