Optomechanical cooling and self-stabilization of a waveguide coupled to a whispering-gallery-mode resonator

TL;DR

This paper demonstrates passive optomechanical cooling and stabilization of a nanospike waveguide coupled to a whispering-gallery-mode resonator, achieving significant temperature reduction and motion suppression through photothermal and optical forces.

Contribution

First demonstration of efficient passive cooling of a waveguide coupled to a WGM resonator, showing strong stabilization via combined photothermal and optical forces.

Findings

Cooling from room temperature to 1.8 K

11.6 dB reduction in mean square displacement

Simultaneous cooling of multiple mechanical modes

Abstract

Laser cooling of mechanical degrees of freedom is one of the most significant achievements in the field of opto-mechanics. Here, we report, for the first time to the best of our knowledge, efficient passive optomechanical cooling of the motion of a freestanding waveguide coupled to a whispering-gallery-mode (WGM) resonator. The waveguide is an 8 mm long glass-fiber nanospike, which has a fundamental flexural resonance at {\Omega}/2{\pi} = 2.5 kHz and a Q-factor of 1.2 10**5. Upon launching 250 {\mu}W laser power at an optical frequency close to the WGM resonant frequency, we observed cooling of the nanospike resonance from room temperature down to 1.8 K. Simultaneous cooling of the first higher-order mechanical mode is also observed. The strong suppression of the overall Brownian motion of the nanospike, observed as an 11.6 dB reduction in its mean square displacement, indicates strong optomechanical stabilization of linear coupling between the nanospike and the cavity mode. The cooling is caused predominantly by a combination of photothermal effects and optical forces between nanospike and WGM resonator. The results are of direct relevance in the many applications of WGM resonators, including atom physics, optomechanics, and sensing.