Initial experiments were undertaken to see if sonoluminescence could
be observed in these liquids. We were able to trap bubbles in alcohol
at temperatures down to -150 F, where the intensity of the sonoluminescence
increased by a factor of more than 100 from its value at room temperature.
At the lowest temperatures we discovered that hemispherical bubbles could be
stably trapped on solid surfaces in the cell, and that they could still emit
sonoluminescence just like the spherical bubbles at the center of the cell.
This work is described in the article: K. R. Weninger, H. Cho, R. A.
Hiller, S. J. Putterman, and G. A. Williams, Sonoluminescence from an Isolated Hemispherical Bubble on a Solid Surface, Phys. Rev. E 56, 6745 (1997).
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We were also able to trap helium bubbles in both liquid nitrogen and
liquid oxygen at even lower temperatures (-350 F), and studied
the characteristics of the bubble oscillations using laser scattering
techniques. However, we were unsuccessful in observing any
sonoluminescence in these liquids; the bubbles would become unstable
and no longer trap as the sound amplitude was increased.
These experiments are described in : O. Baghdassarian, H. Cho, E. Varoquaux,
and G. A. Williams,Trapped Bubble Dynamics in Cryogenic Fluids,
J. Low Temp. Phys. 110, 305 (1998).
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Since the acoustic trapping technique did not seem to work, we
recently turned to another technique for studying bubbles in liquids, which is
to create a single bubble using a focused pulse of laser light. This technique,
pioneered in Russia in the 1970's, creates a single bubble as the liquid is vaporized
by the intense laser energy. The bubble grows to as much as a millimeter in size,
and then collapses, compressing the gas inside, and right at the collapse point a
pulse of light is emitted. We have recently studied this process in great detail for
the case of water at room temperature, and made a number of interesting observations:
We have also recently observed luminescence from laser-created bubbles
in liquid nitrogen and
liquid argon. The unusual feature that we see is a very long pulse duration of the emitted
light, ranging from 100 nanoseconds for the smallest bubbles up to 1000 nanoseconds for the
largest millimeter-sized bubbles. This is about 100 times longer than the pulses we observed
for the similar bubbles in water. We do not understand these interesting observations yet, and
further measurements are being undertaken. A preprint of this
work (accepted for publication in Physica B) can be found on the web here.