B.P. Barber, R. Hiller, K. Arisaka, H. Fetterman, and S. Putterman. "Resolving The Picosecond Characteristics Of Synchronous Sonoluminescence", Journal of the Acoustical Society of America 91 (5), 3061-3063 (May 1992).

The resolution with which the synchronous picosecond flashes of acoustically generated light can be measured has been improved. The flash widths are now found to be considerable less than 50 ps and the jitter in the time between flashes can also be substantially less than 50 ps. The flashes of sonoluminescence appear to turn off very sharply without ringing or after pulsing.

B.P. Barber, R. Hiller, R. Lofstedt, S.J. Putterman and K.R. Weninger. "Defining the Unknowns Of Sonoluminescence", Physics Reports 281 (2), 65-143 (1 March 1997).

As the intensity of a standing sound wave is increased the pulsations of a bubble of gas trapped at a velocity node attain sufficient amplitude so as to emit picosecond flashes of light with a broadband spectrum that increases into the ultraviolet. The acoustic resonator can be tuned so that the flashes of light occur with a clocklike regularity: one flash for each cycle of sound with a jitter in the time between flashes that is also measured in picoseconds. This phenomenon (sonoluminescence or "SL") is remarkable because it is the only means of generating picosecond flashes of light that does not use a laser and the input acoustic energy density must be concentrated by twelve orders of magnitude in order to produce light. Light scattering measurements indicate that the bubble wall is collapsing at more than 4 times the ambient speed of sound in the gas just prior to the light emitting moment when the gas has been compressed to a density determined by its van der Waals hard core. Experiments indicate that the collapse is remarkably spherical, water is the best fluid for SL, some noble gas is essential for stable SL, and that the light intensity increases as the ambient temperature is lowered. In the extremely stable experimental configuration consisting of an air bubble in water, measurements indicate that the bubble chooses an ambient radius that is not explained by mass diffusion. Experiments have not yet been able to map out the complete spectrum because above 6 eV it is obscured by the cutoff imposed by water, and furthermore experiments have only determined an upper bound on the flash widths. In addition to the above puzzles, the theory for the light emitting mechanism is still open. The scenario of a supersonic bubble collapse launching an imploding shock wave which ionizes the bubble contents so as to cause it to emit Bremsstrahlung radiation is the best candidate theory but it has not been shown how to extract from it the richness of this phenomenon. Most exciting is the issue of whether SL is a classical effect or whether Planck's constant should be invoked to explain how energy which enters a medium at the macroscopic scale holds together and focuses so as to be emitted at the microscopic scale.

B.P. Barber and S. Putterman. "Observation of Synchronous Picosecond Sonoluminescence",
Nature 352, 318-320 (25 July 1991).

Sonoluminescence is a non-equilibrium phenomenon in which the energy in a sound wave becomes highly concentrated so as to generate flashes of light in a liquid. We show here that these flashes, which comprise over 10^5 photons, are too fast to be resolved by the fastest photomultiplier tubes available. Furthermore, when sonoluminescence is driven by a resonant sound field, the bursts can occur in a continuously repeating, regular fashion. These precise "clock-like" emissions can continue for hours at drive frequencies ranging from audible to ultrasonic. These bursts represent an amplification of energy by eleven orders of magnitude.

L. A. Crum and G.T. Reynolds, "Sonoluminescence Produced By "Stable" Cavitation", Journal of the Acoustical Society of America 78 (1), 137-139 (July 1985).

This article reports on a phenomenological study of sonoluminescence produced by acoustic cavitation in which a sensitive, high-gain image intensifier tube (EMI type 9912) was used to view the cavitation. We discovered that large amounts of light were being emitted from regions near pressure antinodes in the standing wave field where the pressure amplitude was approximately 0.17 +/- 0.03 MPa. Visual observation of these areas indicated activity resembling "stable" cavitation rather than "transient" cavitation.

L. A. Crum, "Sonoluminescence", Physics Today, 22-29 (September 1994).

A simple mechanical system can produce light from sound. In the process energy densities can increase by a factor of 10^12, and 50-picosecond light pulses are synchronized to a few parts in 10^11.

R.P. Fliller III and H. Metcalf, "Sonoluminescence: Experiment and Experience", Journal of Undergraduate Research 2 (2), 108-121 (Spring 1996).

Sonoluminescence is a phenomenon in which sound is converted into light in a bubble of air trapped in water. The mechanism by which this occurs is as yet poorly understood. The apparatus to produce this phenomenon is relatively simple to construct. The purpose of this paper is to describe the construction of the apparatus used to produce sonoluminescence. Our experiences in building the apparatus are also included to save future experimenters from frustrating problems. A detailed procedure for producing sonoluminescence is also included. The outlined procedures try to remove the guesswork that surrounds this phenomenon. Future plans for our experiment are included with the hope that other groups will start research on sonoluminescence.

D. F. Gaitan and L. A. Crum, "Observation of Sonoluminescence From A Single, Stable Cavitation Bubble In A Water/Glycerene Mixture", Frontiers of Nonlinear Acoustics: Proceedings of 12th ISNA Edited by M.F. Hamilton and D.T. Blackstock, 459-463 (1990).

D. F. Gaitan, L. A. Crum, C. C. Church, and R. A. Roy, "Sonoluminescence and bubble dynamics for a single, stable, cavitation bubble" , Journal of the Acoustical Society of America 91, 3166-3183 (1992).

High-amplitude radial pulsations of a single gas bubble in several glycerine and water mixtures have been observed in an acoustic stationary wave system at acoustic pressure amplitudes on the order of 150 kPa (1.5 atm) at 21-25 kHz. Sonoluminescence (SL), a phenomenon generally attributed to the high temperatures generated during the collapse of cavitation bubbles, was observed as short light pulses occurring once every acoustic period. These emissions can be seen to originate at the geometric center of the bubble when observed through a microscope. It was observed that the light emissions occurred simultaneously with the bubble collapse. Using a laser scattering technique, experimental radius-time curves have been obtained which confirm the absence of surface waves, which are expected at pressure amplitudes above 100 kPa. [S. Horsburgh, Ph.D. dissertation, University of Mississippi (1990)]. Also from these radius-time curves, measurements of the pulsation amplitude, the timing of the major bubble collapse, and the number of rebounds were made and compared with several theories. The implications of this research on the current understanding of cavitation related phenomena such as rectified diffusion, surface wave excitation, and sonoluminescence are discussed.

H.P. Greenspan and A. Nadim, "On Sonoluminescence Of An Oscillating Gas Bubble", Physics Review Letters 5 (4), 1065-1067 (April 1993).

It is proposed that shock dynamics within the gas of a small bubble explains sonoluminescence-the emission of visible radiation in response to spherically symmetric, ultrasonic excitation of a gas bubble in a liquid. As the bubble radius oscillates, shock waves develop from spherical sound waves created inside the gas bubble. As any such shock propagates toward the center, it strengthens and, upon convergence and subsequent reflection, dramatically increases the temperature of the gas behind it. Sufficiently high temperatures are predicted to explain the emission of light by the gas molecules.

D. Hammer and L. Frommhold. "Sonoluminescence: How Bubbles Glow", Journal of Modern Optics 48 (2), 239-277 (2001).

We review recent attempts to elucidate the phenomenon of sonoluminescence in terms of fundamental principles. We focus mainly on the processes which generate the light, but other relevant facts, such as the bubble dynamics, must also be considered for the understanding of the physics involved. Our emphasis is on single bubble sonoluminescence which in recent years has received much attention, but we also look at some of the excellent work on multiple bubble sonoluminescence and its spectral characteristics for clues. The weakly ionized gas models were recently studied most thoroughly and are remarkably successful when combined with a hydrodynamic bubble model, in terms of reproducing observed spectral shapes, intensities, optical pulse widths and the dependencies of these observables on the experimental parameters. Other radiation models, such as proton tunnelling radiation and the confined electron model, were not combined with hydrodynamic models and/or have freely adjustable parameters so that their relevance to sonoluminescence studies is at present less critically tested.

R.A. Hiller and B.P. Barber, "Producing Light From A Bubble Of Air", The Amateur Scientist. Scientific American, 96-98 (February 1995).

R.G. Holt and L.A. Crum, "Acoustically Forced Oscillations of Air Bubbles In Water: Experimental Results", Journal of the Acoustical Society of America 91 (4), 1924-1932 (April 1992).

An experimental technique for measuring the time-varying response of an oscillating, acoustically levitated air bubble in water is developed. The bubble is levitated in a resonant cell driven in the (r,theta,z) mode of (1,0,1) at a frequency fd=24 kHz. Linearly polarized laser light (Ar-I 488.0 nm) is scattered from the bubble, and the scattered intensity is measured with a suitable photodetector positioned at some known angle from the forward, subtending some solid acceptance angle. The output photodetector current, which is linearly proportional to the light intensity, is converted into a voltage, digitized, and then stored on a computer for analysis. For spherical bubbles, the scattered intensity Iexp(t) as a function of radius R and angle theta is calculated theoretically by solving the boundary value problem (Mie theory) for the water/bubble interface. The inverse transfer function R(I) is obtained by integrating over the solid angle centered at some constant theta. Using R(I) as a look-up table, the radius versus time [R(t)] response is calculated from the measured intensity versus time [Iexp(R,t)]. Fourier and phase space analyses are applied to individual R(t) curves. Resonance response curves are also constructed from the R(t) curves for equilibrium radii ranging from 20 to 90 microns, and harmonic resonances are observed. Comparisons are made to a model for bubble oscillations developed by Prosperetti et al. [Prosperetti et al., J. Acoust. Soc. Am. 83, 502 (1988)]. Complex Iexp(t) behavior is also measured, with subharmonics and broadband noise apparent in the Fourier spectra. Possible explanations for this phenomenon are discussed, including shape oscillations and chaos.

A sonoluminescing bubble has been modeled as a thermally conducting, partially ionized, two-component plasma. The model shows that the measured picosecond pulse widths are due to electron conduction and the rapidly changing opacity of the plasma and that these mechanisms are also responsible for the absence of an "afterglow" subsequent to the sonoluminescence flash while the hot bubble expands and cools. The calculated spectra for sonoluminescing nitrogen and argon bubbles suggest that a sonoluminescing air bubble probably contains argon, in agreement with recent theoretical analysis.

S.J. Putterman, "Sonoluminescence: Sound Into Light", Scientific American, 46-51 (February 1995).

A bubble of air can focus acoustic energy a trillionfold to produce picosecond flashes of light. The mechanism eludes complete explanation.

S.J. Putterman, "Sonoluminescence: The Star In A Jar", Physics World, 38-42 (May 1998).

How can sound be transformed into a brief flash of light? Recent experiments have provided new insights into this remarkable phenomenon, but its cause is no yet fully understood.

K. Suslick, "Sonochemistry", Science 247, 1439-1445 (March 1990).

Ultrasound causes high-energy chemistry. It does so through the process of acoustic cavitation: the formation, growth and implosive collapse of bubbles in a liquid. During cavitational collapse, intense heating of the bubbles occurs. These localized hot spots have temperatures of roughly 5000? C, pressures of about 500 atmospheres, and lifetimes of a few microseconds. Shock waves from cavitation in liquid-solid slurries produce high-velocity interparticle collisions, the impact of which is sufficient to melt most metals. Applications to chemical reactions exist in both homogeneous liquids and in liquid-solid systems. Of special synthetic use is the ability of ultrasound to create clean, highly reactive surfaces on metals. Ultrasound has also found important uses for initiation or enhancement of catalytic reactions, in both homogeneous and heterogeneous cases.

G. Vazquez, C. Camara, S. Putterman, and K. Weninger, "Sonoluminescence: Nature's Smallest Blackbody", Optics Letters, 26 (9), 575-577 (May 1998).

The transduction of sound into light through the implosion of a bubble of gas leads to a flash of light whose duration is delineated in picoseconds. Combined measurements of spectral irradiance, Mie scattering, and flash width (as determined by time-correlated single-photon counting) suggest that sonoluminescence from hydrogen and noble-gas bubbles is radiation from a blackbody with temperatures ranging from 6000 K H 2 to 20,000K(He) and a surface of emission whose radius ranges from 0.1 m m He to 0.4 m m Xe . The state of matter that would admit photon matter equilibrium under such conditions is a mystery.

Articles that might be used:

Sonoluminescence spectra of the heavy rare gases are calculated by combining the Hilgenfeldt et al. model of sonoluminescence [Phys. Fluids 11, 1318 (1999)] with quantum line-shape calculations of electron-neutral-atom bremsstrahlung spectra [L. Frommhold, Phys. Rev. E 58, 1899 (1998)]. Good agreement between theoretical and experimental spectra is obtained by choosing values of the ambient radius R0 and acoustic pressure amplitude Pa that are compatible with diffusive equilibrium calculations.

K. Yasui, "Effect of Thermal Conduction of Bubble Dynamics Near The Sonoluminescence Threshold", J. Acoust. Soc. Am. 98 (5), 2772-2782 (1995).