  We present a description of a strongly driven multimode optomechanical system
that shows the emergence of cooperative effects usually known from systems of
atom-light interaction. Our calculations show that under application of a
coherent pump field the system's response can be switched from a superradiant
regime to a collective gain regime by varying the frequency detuning of the
pump. In the superradiant regime, enhanced optical cooling of a single
vibrational mode is possible, whereas the collective gain regime would
potentially enable one to achieve almost thresholdless phonon laser action. The
threshold pumping power scales as 1/N.
