Doppler cooling a microsphere.

Doppler cooling the center-of-mass motion of an optically levitated microsphere via the velocity-dependent scattering force from narrow whispering gallery mode resonances is described. Light that is red detuned from the whispering gallery mode resonance can be used to damp the center-of-mass motion in a process analogous to the Doppler cooling of atoms. The scattering force is not limited by saturation but can be controlled by the incident power. Cooling times on the order of seconds are calculated for a 20 μm diameter silica microsphere trapped within optical tweezers.