  The maximum amplitude of mechanical oscillators coupled to optical cavities
are studied both analytically and numerically. The optical backaction on the
resonator enables self-sustained oscillations whose limit cycle is set by the
dynamic range of the cavity. The maximum attainable amplitude and the phonon
generation quantum efficiency of the backaction process are studied for both
unresolved and resolved cavities. Quantum efficiencies far exceeding one are
found in the resolved sideband regime where the amplitude is low. On the other
hand the maximum amplitude is found in the unresolved system. Finally, the role
of mechanical nonlinearities is addressed.

Optics