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|  File Name      : SONOLUM2.ASC     |  Online Date     :  11/24/94          |
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The sonoluminescence story is getting more interesting every month.
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From Science News, Vol. 146, October 15, 1994

                   Making light of sound in solitary bubbles

Trapped in an intense sound wave, a tiny gas bubble in water can emit a string
of flashes bright enough to be visible in an undarkened room.  Producing a
startling sound-and-light show on an intriguingly small scale, this simple
system serves as a remarkable laboratory for physics and chemistry.

Now, researchers have demonstrated that slight changes in the composition of
the gas inside such a bubble can strongly influence the intensity and
wavelengths of the light that escapes.  For example, adding a small amount of
argon, xenon, or helium to a nitrogen bubble substantially increases the
intensity of ultraviolet light emission.

Physicists Robert Hiller, Keith Weninger, Seth J. Putterman, and Bradley P.
Barber of the University of California, Los Angeles, describe their findings
in the Oct. 14 SCIENCE.

When an intense sound wave travels through the water it creates microscopic
cavities that immediately fill with gas originally dissolved in the liquid.
Such bubbles alternately expand and contract in step with regular changes in
the sound wave's pressure.

During the contraction phase, a bubble can collapse so violently and rapidly
that it concentrates the sound energy sufficiently to heat the enclosed gas to
temperatures exceeding 10,000 kelvins.  The heated gas luminesces, giving off
an extremely bright flash of visible and ultraviolet light lasting less than
50 picoseconds.

Although researchers have known about this effect - called sonoluminescence -
since the 1930s, they still do not have a complete understanding of how it
works (SN:10/23/93, p.271).  The experiments of Hiller and his coworkers
represent one attempt to elucidate the process.

The researchers found that raising the noble gas content of a nitrogen bubble
in water to 1 precent dramatically stabilizes the bubble's motion.  It also
increases the intensity of light emission by a factor of at least 10.

At the same time, the spectrum of available light generated by a bubble
depends strongly on the gas inside the cavity.  A bubble containing argon
produces ultraviolet light that peaks at a wavelength of 300 nanometers.
However, a helium-laced bubble shows no such peak.

"Some exciting atomic physics may be occurring within the collapsing
cavitation bubble that gives rise to [single-bubble sonoluminescence],"
Lawrence A. Crum and Ronald A. Roy of the University of Washington in Seattle
comment in the same issue of SCIENCE.  "However, many of the results [Hiller
and his colleagues] present are also anomalous and defy immediate
explanation."

Clearly, further investigations are necessary to pin down how sonoluminescence
occurs.  At the same time, the new results suggest the possibility of using
gas impurities for improved control of the characteristics of light emissions
from collapsing bubbles.   - I. Peterson

I would like to point out that Norman Wootan has stated in the past that he
believes the noble gases are one of the keys to free energy, and the new
research on sonoluminescence and the increase of energy output by using noble
gases in the collapsing bubble only bolster this position.  It seems that
argon, xenon, neon, and helium may not only be pivotal in plasma energy
production, but in enhanced sonoluminescence as well!  >>  Bert
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