Laser linewidth hazard in optomechanical cooling

I discuss the robustness of pumped cavity dynamics against phase diffusion of the laser and conclude that optomechanical cooling has extreme sensitivity compared to laser cooling of atoms. Certain proposals for ground-state optomechanical cooling by a single cavity would require an unrealistically sharp laser linewidth or, equivalently, a very low level of phase noise. A systematic way to cancel classical excess phase noise is the interferometric twin-cavity pumping, initiated for optically trapped macromirrors of future gravitational-wave detectors.