Simultaneous High-Speed Recording of Sonoluminescence and Bubble Dynamics in Multibubble Fields

Carlos Cairós and Robert Mettin

Phys. Rev. Lett. 118, 064301 – Published 8 February 2017

Abstract

Multibubble sonoluminescence (MBSL) is the emission of light from imploding cavitation bubbles in dense ensembles or clouds. We demonstrate a technique of high-speed recording that allows imaging of bubble oscillations and motion together with emitted light flashes in a nonstationary multibubble environment. Hereby a definite experimental identification of light emitting individual bubbles, as well as details of their collapse dynamics can be obtained. For the extremely bright MBSL of acoustic cavitation in xenon saturated phosphoric acid, we are able to explore effects of bubble translation, deformation, and interaction on MBSL activity. The recordings with up to 0.5 million frames per second show that few and only the largest bubbles in the fields are flashing brightly, and that emission often occurs repetitively. Bubble collisions can lead to coalescence and the start or intensification of the emission, but also to its termination via instabilities and splitting. Bubbles that develop a liquid jet during collapse can flash intensely, but stronger jetting gradually reduces the emissions. Estimates of MBSL collapse temperature peaks are possible by numerical fits of transient bubble dynamics, in one case yielding 38 000 K.

Received 26 May 2016

DOI:https://doi.org/10.1103/PhysRevLett.118.064301

Physics Subject Headings (PhySH)

Cavitation Drops & bubbles Sonoluminescence

Fluid Dynamics

Authors & Affiliations

Carlos Cairós and Robert Mettin^*

Christian Doppler Laboratory for Cavitation and Micro-Erosion, Drittes Physikalisches Institut, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

^*Corresponding author. robert.mettin@phys.uni-goettingen.de

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Issue

Vol. 118, Iss. 6 — 10 February 2017

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Images

Figure 1
Sample images from high-speed recordings at different frame rates and magnifications. Top: setup $A$ , 36.5 kHz; large emitting bubbles run from right to left in a streamer, often followed by a “flock” of smaller bubbles. Bottom: setup $B$ , 23 kHz; large emitting bubbles run partly back and forth in the vicinity of a dense bubble cloud closer to the ultrasound emitter. SL can occur together with pronounced jetting (indicated by an elongated bulge during bubble reexpansion). See also Supplemental Material videos [25].
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Figure 2
Different collision scenarios of SL bubbles. (a) Similarly sized emitting bubbles merge and flash brighter (36.5 kHz, $5000 frames / \sec$ ). (b) An SL bubble in a swarm of smaller bubbles merges with a similarly sized neighbor, becomes shape unstable, and disintegrates. The emission ceases (36.5 kHz, $5000 frames / \sec$ ). (c),(d) Enlargements of the collision process from (b) at 0.8 and 1.0 ms [frame width in (c): $125 μ m$ , in (d): $137 μ m$ ]. (e) A larger SL bubble shows emission directly in the first collapse after a merger with a smaller bubble (23 kHz, $75 000 frames / \sec$ , frame-to-frame time $13.3 μ s$ ). Images are processed for better printing.
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Figure 3
Collapse events and light emissions of an accelerating large bubble that develops jetting (23 kHz, $150 000 frames / \sec$ , timing given in $μ s$ , frame width $470 μ m$ ). For each collapse, two subsequent frames are shown (full data in the Supplemental Material [25]).
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Figure 4
Observation of a transient bubble oscillation with extremely bright emission (23 kHz, $525 000 frames / \sec$ ). (a) Part of the high-speed recording presented as collocated stripes, time proceeds linewise from top to bottom (scale indicated). (b) Radius-time data (red crosses) and numerical fit (dashed blue line) with pressure amplitude $p_{a} = 184.6 kPa$ and equilibrium bubble radius $R_{0} = 36.7 μ m$ , which reproduce the peculiar aperiodic bubble oscillation quite well [see also Supplemental Material, part II]. Maximum pixel readouts of the identified SL flashes are depicted as negative-going red bars below the zero line. The frames shown correspond to the time interval between 100 and $406 μ s$ . For the strongest SL signal around $220 μ s$ , the inset shows the model results for temperature $T$ [K], bubble wall speed $| d R / d t |$ [ $m / s$ ], and sound speed in the heated xenon gas $c_{Xe (T)}$ [ $m / s$ ]. Since jetting, evaporation or condensation and chemistry are not included in the model, the values are supposed to be upper bounds.
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