A laser drives an optical cavity formed by a fixed mirror and a nanoscale mechanical membrane. Radiation pressure couples the light field to the membrane's motion. Depending on the laser's detuning from the cavity resonance, the light either damps (cools) or amplifies (heats) the mechanical oscillation — the same back-action used in LIGO-style mirrors and lab cavity-optomechanics cooling to near the quantum ground state.
Γeff = Γm + g² [ κ / ((Δ-Ωm)²+(κ/2)²) − κ / ((Δ+Ωm)²+(κ/2)²) ]
n_final ≈ Γm·nth / Γeff (sideband cooling limit)
- Mode — flips the sign of the effective detuning: red-detuned cools the membrane, blue-detuned heats/amplifies it.
- Laser power — sets the intracavity photon number and hence the optomechanical coupling strength g.
- Cavity detuning Δ — laser frequency offset from resonance, in units of the cavity linewidth κ; controls cooling vs. heating balance.
- Mechanical Q factor — how weakly the membrane is damped intrinsically; higher Q means the laser back-action dominates more easily.
- Drive frequency offset — an extra resonant drive that reinjects mechanical energy, useful for exploring parametric instability near the heating branch.
Real devices: silicon-nitride membranes and photonic-crystal "zipper" cavities are laser-cooled this way to prepare mechanical resonators near their motional ground state for quantum sensing and gravitational-wave-detector mirror cooling.