Mechanical oscillation and cooling actuated by the optical gradient force

TL;DR

This paper demonstrates how optical gradient forces in a silica microcavity can induce large mechanical oscillations and achieve cooling, with very low power thresholds and significant temperature reduction.

Contribution

It introduces a novel microcavity design that combines strong optical gradient forces with high-Q feedback for efficient mechanical control.

Findings

Mechanical oscillations triggered at 270 nW power

Achieved 13-dB cooling of mechanical motion

Demonstrated strong dynamical backaction in microcavity

Abstract

In this work we combine the large per-photon optical gradient force with the sensitive feedback of a high quality factor whispering-gallery microcavity. The cavity geometry, consisting of a pair of silica disks separated by a nanoscale gap, shows extremely strong dynamical backaction, powerful enough to excite giant coherent oscillations even under heavily damped conditions (mechanical Q=4). In vacuum, the threshold for regenerative mechanical oscillation is lowered to an optical input power of only 270-nanoWatts, or roughly 1000 stored cavity photons, and efficient cooling of the mechanical motion is obtained with a temperature compression factor of 13-dB for 4-microWatts of dropped optical input power.