  We present a simple classical analysis of light interacting with a
Fabry-Perot cavity consisting of a fixed (dielectric) front mirror and a
vibrating rear mirror. In the adiabatic approximation, the returning light
exhibits sideband symmetry, which will go away once the photon lifetime becomes
comparable to or longer than the oscillation period of the rear mirror. When
the oscillation period is short compared to the cavity photon lifetime, one
must approach the problem differently, treating the vibrating mirror as a
scatterer which sends a fraction of the incident light into sideband
frequencies. With proper detuning, the cavity's internal radiation pressure
could either dampen or amplify the vibrations of the mirror; the former is the
physical principle behind opto-mechanical cooling by the back-action of cavity
photons.
