Single Bubble Sonoluminescence

Maaneli Derakhshani, John Noé, Harold Metcalf, Laser Teaching Center, 
Department of Physics and Astronomy, Stony Brook University.

Single bubble sonoluminescence (SBSL) is the process whereby ultrasonic
sound waves cause the growth and collapse of micron-size air bubbles, the
consequence of which is the emission of energy in the form of
picosecond-long flashes of light. The phenomenon is of considerable
interest due to the production of temperatures exceeding 10,000 Kelvin on
the surface of the bubble, and the lack of consensus among researchers on
the details of the physical mechanism. The conventional method by which
SBSL is produced involves injecting a gas bubble into a small spherical
flask of degassed water that is oscillating at its fundamental resonant
frequency of ~26 kHz; two piezoelectric transducers (PZTs) on opposite
sides of the flask create the standing wave pattern. The bubble is
attracted to the pressure anti-node at the center of the flask, where it
repeatedly expands and contracts as a result of the changing sound wave
pressure in the surrounding liquid. The rapid collapse of the bubble
causes it to emit photons which peak in the ultraviolet.
   
To date this study has focused on getting an existing dormant setup back
into operation and developing a quantitative understanding of key
experimental parameters in SBSL, such as producing sufficiently intense
sound waves and achieving the optimum concentration of dissolved gas in
water. In addition, a number of connections between SBSL and other fields
of study have been explored, such as the use of SBSL as a black hole
analogue model, and the discovery and use of acoustical (as opposed to
optical) vortices to induce a torque on a sonoluminescing bubble.
Laser-induced cavitation was also studied for its potential use as a means
of investigating claims of "bubble fusion." One of us (MD) even toured a
large sonoluminescence display set up at an art gallery in New York City.

The PZT's used to produce sound waves in our setup are driven by a series
resonant circuit connected to a voltage-to-current amplifier. The op-amp
circuit was analyzed and an equation was derived to model its behavior.
Several components of the SL apparatus were also repaired, such as the
microphone transducer, the vacuum pump valves and gauge meter, and one of
the PZT drivers. Experiments related to quantifying the amount of air
dissolved in water were more time consuming. The goal was to use the
pressure rise in a closed vacuum system holding the degassed water as an
indicator, but the dissolved gas was found to be released unexpectedly
slowly, over many days. Alternative techniques for measuring the dissolved
air are now being explored.

The current work will continue here in the fall, with the initial goal of
consistently producing SBSL and enhancing visible light output by using
additives such as glycerin or the wavelength-shifter luminol.  Further
studies will attempt to measure bubble size through Mie scattering and
investigate the effects of magnetic fields on bubble stability.

This study was supported by NSF Grant No. PHY-0243935.

1 August 2005