Sonoluminescence

from http://www-phys.llnl.gov/N_Div/sonolum/

Sonoluminescence: an Introduction

About the LLNL sonoluminescence experiment

What is sonoluminescence?

Sonoluminescence is the emission of light by bubbles in a liquid excited by sound. It was first discovered by scientists at the University of Cologne in 1934, but was not considered very interesting at the time.[1]

In recent years, a number of researchers have sought to understand this phenomenon in more detail. A major breakthrough occurred when Gaitan et al. were able to produce single-bubble sonoluminescence, in which a single bubble, trapped in a standing acoustic wave, emits light with each pulsation.[2] Before this development, research was hampered by the instability and short lifetime of the phenomenon.

Why is sonoluminescence so interesting?

Sonoluminescence has created a stir in the physics community. The mystery of how a low-energy-density sound wave can concentrate enough energy in a small enough volume to cause the emission of light is still unsolved. It requires a concentration of energy by about a factor of one trillion. To make matters more complicated, the wavelength of the emitted light is very short - the spectrum extends well into the ultraviolet. Shorter wavelength light has higher energy, and the observed spectrum of emitted light seems to indicate a temperature in the bubble of at least 10,000 degrees Celsius, and possibly a temperature in excess of one million degrees Celsius.

Such a high temperature makes the study of sonoluminescence especially interesting for the possibility that it might be a means to achieve thermonuclear fusion.[3] If the bubble is hot enough, and the pressures in it high enough, fusion reactions like those that occur in the Sun could be produced within these tiny bubbles.

What do we know about sonoluminescence?

The study of sonoluminescence has yielded more puzzles than it has solid clues. Here is a summary of what we know about sonoluminescence:

  • The light flashes from the bubbles are extremely short - less than 12 picoseconds (trillionths of a second) long.[4]
  • The bubbles are very small when they emit the light - about 1 micrometer (thousandth of a millimeter) in diameter.
  • Single-bubble sonoluminescence pulses can have very stable periods and positions. In fact, the frequency of light flashes can be more stable than the rated frequency stability of the oscillator making the sound waves driving them.
  • For unknown reasons, the addition of a small amount of noble gas (such as helium, argon, or xenon) to the gas in the bubble increases the intensity of the emitted light dramatically.[5]

References:

  1. B27, 421 (1934)
  2. L. A. Crum, R. A. Roy, and C. C. Church, J. Acoust. Soc. Am. 91, 3166 (1992)
  3. S. Putterman, Phys. Rev. Lett. 72, 1380 (1994)
  4. M. J. Moran, R. E. Haigh, M. E. Lowry, D. R. Sweider, G. R. Abel, J. T. Carlson, S. D. Lewia, A. A. Atchley, D. F. Gaitan, and X. K. Maruyama, Nucl. Instr. Meth. B 96, 651 (1995)
  5. S. J. Putterman, B. P. Barber, Science 266, 248 (1994)

A few more resources for further information

  1. "Sonoluminescence," L. A. Crum and R. A. Roy, Science 266, 233 (1994)
  2. "Sonoluminescence: Sound into Light," S. J. Putterman, Scientific American, Feb. 1995, p.46
  3. "Bubble Shape Oscillations and the Onset of Sonoluminescence," M. P. Brenner, D. Lohse, and T. F. Dupont, Phys. Rev. Lett. 75, 954 (1995)
  4. The LLNL Sonoluminescence Experiment

This page was prepared by David Knapp, [email protected].