Light-emitting bubbles captured in the wild
Physicists from the University of Göttingen image, for the first time, flashes of light emitted by collapsing bubbles in a bubble cloud
High-power ultrasound is used for cleaning surfaces or wastewater as well as for destroying kidney stones. These applications use a curious effect caused when ultrasound enters liquids: bubbles are generated that periodically grow and collapse. Imploding bubbles compress the gas they contain so strongly that light is emitted from the resulting “hot spot” – a phenomenon called sonoluminescence. At the University of Göttingen, physicists Dr. Carlos Cairós and Dr. Robert Mettin have imaged, for the first time, sonoluminescence flashes together with the bubbles in an ultrasonically driven bubble cloud. By high-speed video recording with up to 0.5 million images taken per second, light emitting bubbles can be identified and their shapes and oscillations analyzed. The scientists published their work in the journal Physical Review Letters.
While collapse and light emission of isolated bubbles have been well studied before in so-called bubble traps, the Göttingen experiments provide a major step towards understanding sonoluminescence in a more realistic environment of applications of high-power ultrasound: chaotic “wild” ensembles of many moving and interacting bubbles, where collisions and splitting of bubbles frequently occur. “A particular observation is that the light-emitting bubbles do not need to be perfectly spherical – which would be the optimum shape for the extreme energy focusing in the collapse”, says Dr. Cairós. “Even bubbles pierced by a liquid jet are observed to emit light, a fact that might explain certain chemical reactions in the bubbles.” The observation technique developed in Göttingen can detect which bubbles in a cloud produce light and can also quantify the intensity. “This photometry of sonoluminiscence may help to optimise applications of high-power ultrasound”, says Dr. Mettin.
The study was conducted in the framework of the “Christian Doppler Laboratory for Cavitation and Micro-Erosion“, a research project funded jointly by the Austrian government and the Austrian-based company Lam Research AG. The project investigated innovative methods of surface cleaning for the semiconductor industries during the past seven years, in parallel with studying the fundamentals of bubble formation in liquids.
Original publication: Carlos Cairós, Robert Mettin, Simultaneous High-Speed Recording of Sonoluminescence and Bubble Dynamics in Multibubble Fields, Physical Review Letters 118, 064301 (2017), DOI: 10.1103/PhysRevLett.118.064301
Dr. Robert Mettin
Georg-August-Universität Göttingen, Faculty of Physics – III. Institute
Christian Doppler Laboratory for Cavitation and Micro-Erosion
Friedrich-Hund-Platz 1, 37077 Göttingen
Phone: +49 (0)551 39-22285