Sonoluminescence

Sonoluminescence: From Sound to Light

Sonoluminescence (SL) is a fascinating effect of the light emission from the gaseous bubbles in liquids. The SL bubbles are driven by ultrasonic field, which makes them oscillate with ultrasonic frequency. If bubbles are driven strongly enough, short bursts of light are emitted once during each period of the sound field.

The effect have been known for many years. But, just recently it become possible to produce single bubble SL, and to get much better insight into the effect and its characteristics.

We have done a considerable amount of theoretical research in the field of sonoluminescence. The research started around 1992, when only very little was known about SL. We formulated few theoretical models with the goal of explaining the effect. Our research from this "early" period is summarized in the following papers:

L. Kondic and Joel I. Gersten, Theory of the Origin of Brief Sonoluminescence Light Pulses (1992).
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L. Kondic and Joel I. Gersten, Sonoluminescence: A theoretical overview (1993).
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New experimental results, which appeared in parallel with our work, gave us an idea that the effect responsible for the SL probably has to do with the emission of the shock wave(s) in a bubble. We solved the gas dynamics equation in the bubble combined with the equation which governs the motion of the bubble boundary and were able to confirm the experimental predictions - shock waves were really produced in the SL bubbles. On the course of research, we realized that extremely high temperatures and pressures develop in the SL bubbles, and that it is necessary to go behind fluid dynamics to really understand the physics of the hot gas in the bubbles. Correspondingly we included the losses of energy because of variety of physical processes going on in the gas in the bubbles. This allowed us to formulate the realistic model for the bubble dynamics, shock production and the emission of visible light (SL pulse). This work has been summarized in two of our papers:

L. Kondic, Joel I. Gersten and Chi Yuan, Radiation from a Sonoluminescencing Bubble (1994)
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L. Kondic, Joel I. Gersten and Chi Yuan, Theoretical Studies of Sonoluminescence Radiation: Radiative transfer and parametric dependence , Physical Review E 52, 4976 (1995).
- Abstract
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- Figures .
- PDF (complete version)
The temperature profiles in the bubble, about the time when it radiates sonoluminescent pulse are given bellow. Time in in picoseconds; zero of time is chosen as the time when bubble radius reaches its minimum value. Bubble radius almost does not change during this short time. At t=-35 ps (profile 1), shock wave just started to form - note lower temperature in the bubble center. The shock implodes towards the center and reaches it at t=-2.4 ps (profiles 1-6). It rebounds, producing high temperature (measured in hundreds of thousands, if not millions of degrees) at the bubble center.
Profiles 7-12 show the rebounded shock wave which propagates outwards, hits the bubble wall (t= -0.4 ps), partially rebounds again, collapses towards the center (t=0.5 ps), and rebounds again. A lot of action during the time which is million times shorter than period of bubble oscillations. And bubble oscillates 26,000 times in one second!

Still, many questions remain unanswered. One of them is that a small change in the bubble content (e.g. change of the amount of noble gas) leads to drastic changes in the SL emission. Experimental results suggest that the stability of the bubble oscillations with respect to the small disturbances of its (presumably) spherical shape might be responsible for this observation. This part of our research is summarized in
- L. Kondic and Joel I. Gersten, Stability of the Sonoluminescing Bubbles (1995).
  - Abstract
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Some insight into the above mentioned questions can be reached by modifying another available experimental parameter, and that is ambient pressure. Previously developed shock theory of SBSL, combined with the study of bubble stability and mass transfer between the bubble and the surrounding liquid predict some intriguing results. In particular, the theory predicts a 200% increase in SL radiation if ambient pressure is decreased only 5%. Preliminary comparison with available experimental results encourages further research in this direction.
- L. Kondic, Chi Yuan and C.K. Chan, Ambient pressure and single-bubble sonoluminescence , Physical Review E 57, 32 (1998).
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We continue our research in the field of sonoluminescence, and hope to contribute to the better understanding of the physical and chemical processes relevant to this fascinating effect.
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