Fundamental thermal noise in droplet microresonators

TL;DR

This paper experimentally investigates thermal noise in liquid droplet microresonators, revealing that surface fluctuations significantly impact optical quality and identifying the dominant noise sources affecting photon lifetime.

Contribution

It provides the first experimental measurement of thermal surface distortions in droplet microresonators and distinguishes intrinsic losses from thermal effects using transient cavity ring-down spectroscopy.

Findings

Photon lifetime exceeds thermal limit by ten times

Capillary fluctuations activate surface scattering

Thermal surface distortions significantly affect optical quality

Abstract

Liquid droplet whispering-gallery-mode microresonators open a new research frontier for optomechanics and photonic devices. At visible wavelengths, where most liquids are transparent, a major contribution to a droplet optical quality factor is expected theoretically from thermal surface distortions and capillary waves. Here, we investigate experimentally these predictions using transient cavity ring-down spectroscopy. In this way, the optical out-coupling and intrinsic loss are measured independently while any perturbation induced by thermal, acoustic and laser-frequency noise is avoided thanks to the ultra-short light-cavity interaction time. The measurements reveal a photon lifetime ten times longer than the thermal limit and suggest that capillary fluctuations activate surface scattering effects responsible for light coupling.