Interferometric detection of hydrodynamic bubble–bubble interactions

Abstract

We report a new interferometric method to study the interactions between two gas bubbles undergoing small-amplitude oscillations in a liquid, based on the extension of a previously developed one-bubble set-up. Nanometric oscillations of millimetre-sized supported bubbles are excited acoustically; the response of each bubble is recorded interferometrically, as a function of the mutual distance (from quasi-contact to greater than the bubbles radii). The interferometric nature of the technique and the resonant nature of the vibration modes enable the accurate measurement of the amplitude (with sub-nanometric sensitivity), frequency and mutual phase of oscillation, whose variations over the bubble–bubble distance range allow the interactions to be probed. The bubbles oscillate at the same frequencies, exhibiting a low-frequency, in-phase and a high-frequency, out-of-phase resonance peak, whose separation is a function of distance, in good agreement with the theory for free interacting bubbles. The technique, here demonstrated for the volume modes of air bubbles in water, can be extended to other gas–liquid and liquid–liquid interfaces, bare or adsorbate-covered, as well as to shape oscillations.

Biomechanical Sensing Using Gas Bubbles Oscillations in Liquids and Adjacent Technologies: Theory and Practical Applications

“…Finally, in this section we review an acousto-optical sensing mechanism that exploits gas bubbles and employs an interferometric optical technique to detect the changes in their shape and to investigate interactions between two bubbles undergoing small-amplitude oscillations [ 221 ]. This sensing approach relies on the ability of air–liquid interfaces to reflect light similarly to mirrors of a Fabry–Perot interferometer.…”

“…The inset shows schematically the detection principle, where a laser beam focused on a bubble undergoes reflections at the curved interfaces (points S1 and S2) generating an interference pattern in the direction opposite to that of the incident laser beam. Reproduced with permission from [ 221 ]. Copyright 2022 Cambridge University Press.…”

Gas Bubble Photonics: Manipulating Sonoluminescence Light with Fluorescent and Plasmonic Nanoparticles

“…A soap bubble floating in the air, air bubbles rising from a scuba diver in water and bubbles of gas rising in a soft drink are just a few examples of one remarkable physical phenomenon that most of us know since our childhood [1,2]. We can see an air bubble in water because the optical refractive index of air is approximately 1 but that of water is approximately 1.33, which, according to Snell's law [3], allows identifying a bubble due to the effect of optical refraction [4] and internal reflection processes [5].…”

Biomechanical Sensing using Gas Bubbles Oscillations in Liquids and Adjacent Technologies: Theory and Practical Applications

“…Finally, in this section we review an acousto-optical sensing mechanism that exploits 904 gas bubbles and employs an interferometric optical technique to detect the changes in 905 the bubble shape and to investigate interactions between two bubbles undergoing small-906 amplitude oscillations in a liquid [221]. This sensing approach relies on the ability of 907 air-liquid interfaces to reflect light similarly to mirrors of a Fabry-Perot interferometer.…”

“…The inset schematically shows the detection principle, where a laser beam focused on a bubble undergoes reflections at the curved interfaces (points S1 and S2) generating an interference pattern in the backward direction with respect to the direction of the incident laser beam. Reproduced with permission from[221].Copyright 2022 Cambridge University Press.…”