Sonoluminescence

Article By:

Lohse, Detlef Faculty of Applied Physics, University of Twente, Enschede, The Netherlands.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.757754

The transformation of acoustic energy into light through collapsing bubbles. In particular, single-bubble sonoluminescence (SBSL) is the periodic light emission of a single acoustically trapped and periodically driven gas bubble. It occurs when the bubble collapses so violently that the energy focusing during collapse is intense enough for partial ionization of the gas inside the bubble to occur, leading to subsequent light emission. The phenomenon of single-bubble sonoluminescence was discovered in 1989 by Felipe Gaitan, then a graduate student, working with Lawrence A. Crum. A micrometer-sized bubble is acoustically trapped in a water-filled flask at resonance. The driving pressure is typically P_a = 1.2–1.4 bar (1 bar = 10⁵ Pa ≅ 1 atm), the driving frequency is 20–40 kHz, and the air saturation in the water is typically 20–40%. Once per cycle, at bubble collapse, the bubble emits a short pulse of light, that typically lasts 100–300 picoseconds. The origin of the light is thermal bremsstrahlung: During the adiabatic collapse, the gas inside the bubble is heated, presumably to about 15,000 K. Consequently, the gas partly ionizes. The ions and electrons interact, decelerate, and finally recombine, and the deceleration is connected with light emission. See also: Bremsstrahlung

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