  The coupling of mechanical and optical degrees of freedom via radiation
pressure has been a subject of early research in the context of gravitational
wave detection. Recent experimental advances have allowed studying for the
first time the modifications of mechanical dynamics provided by radiation
pressure. This paper reviews the consequences of back-action of light confined
in whispering-gallery dielectric micro-cavities, and presents a unified
treatment of its two manifestations: notably the parametric instability
(parametric amplification) and radiation pressure back-action cooling.
Parametric instability offers a novel "photonic clock" which is driven purely
by the pressure of light. In contrast, radiation pressure cooling can surpass
existing cryogenic technologies and offers cooling to phonon occupancies below
unity and provides a route towards cavity Quantum Optomechanics
