Smectic and soap bubble optofluidic lasers

TL;DR

This paper introduces soap and smectic liquid crystal bubbles as novel optical cavities supporting whispering gallery mode lasing, enabling highly sensitive electric field and pressure sensing with potential for future applications in thin film and optomechanics studies.

Contribution

It demonstrates for the first time that soap and smectic bubbles can support whispering gallery mode lasing and serve as ultra-sensitive sensors for electric fields and pressure.

Findings

Supported whispering gallery mode lasing in soap and smectic bubbles.

Achieved nanometer-scale size change detection.

Developed sensors with high sensitivity and wide dynamic range.

Abstract

Soap bubbles are simple, yet very unique and marvelous objects. They exhibit a number of interesting properties such as beautiful interference colors and the formation of minimal surfaces. Various optical phenomena have been studied in soap films and bubbles, but so far they were not employed as optical cavities. Here we demonstrate, that dye doped soap or smectic liquid crystal bubbles can support whispering gallery mode lasing, which is observed in the spectrum as hundreds of regularly spaced peaks, resembling a frequency comb. The lasing enabled the measurement of size changes as small as 10 nm in a millimeter-sized, $\sim$100 nm thick bubble. Bubble lasers were used as extremely sensitive electric field sensors with a smallest measurable electric field of 110 Vm$^{-1}$Hz$^{-1/2}$. They also enable the measurement of pressures up to a 100 bar with a resolution of 1.5 Pa, resulting in a dynamic range of almost $10^7$. By connecting the bubble to a reservoir of air, almost arbitrarily low pressure changes can be measured while maintaining an outstanding dynamic range. The demonstrated soap bubble lasers are a very unique type of microcavities which are one of the best electric field and pressure microsensors to date and could in future also be employed to study thin films and cavity optomechanics.