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Researchers build an ultrasound
version of the laser
Kloeppel, Physical Sciences Editor
photo to enlarge
by L. Brian Stauffer
Weaver, a professor of theoretical and applied mechanics
at Illinois, and colleagues at Illinois and the University
of MIssouri-Rolla, have built an ultrasound analogue
of the laser.
— Researchers at the University of Illinois at Urbana-Champaign
and at the University of Missouri-Rolla have built an ultrasound analogue
of the laser.
Called a uaser (pronounced WAY-zer) – for ultrasound amplification
by stimulated emission of radiation, the instrument produces ultrasonic
waves that are coherent and of one frequency, and could be used to study
laser dynamics and detect subtle changes, such as phase changes, in
“We have demonstrated that the essential nature of a laser can
be mimicked by classical mechanics – not quantum mechanics –
in sound instead of light,” said Richard Weaver, a professor of theoretical and applied mechanics at Illinois.
To make a uaser, Weaver, Illinois research associate Oleg Lobkis and
UMR physics professor Alexey Yamilov begin by mounting a number of piezoelectric
auto-oscillators to a block of aluminum, which serves as an elastic,
acoustic body. When an external acoustic source is applied to the body,
the oscillators synchronize to its tone. Like fireflies trapped in a
bottle, the oscillators synchronize to the frequency of the source.
In the absence of an external source, the tiny ultrasonic transducers
become locked to one another by virtue of their mutual access to the
same acoustic system.
“The phases must be correct also,” Weaver said. “By
carefully designing the transducers, we can assure the correct phases
and produce stimulated emission. As a result, the power output scales
with the square of the number of oscillators.”
The uaser more closely resembles a “random laser” than it
does a conventional, highly directional laser, Weaver said. “In
principle, however, there is no reason why we shouldn’t be able
to design a uaser to generate a narrow, highly directional beam.”
Optical lasers are useful because of their coherent emission, high intensity
and rapid switching. These features are of little value in acoustics,
where coherence is the rule and not the exception, intensity is limited
by available power, and maximum switching speeds are limited by moderate
Nevertheless, uasers may be useful. With their longer wavelengths and
more convenient frequencies, uasers could prove useful for modeling
and studying laser dynamics. They could also serve as highly sensitive
scientific tools for measuring the elastic properties and phase changes
of modern materials, such as thin films or high-temperature superconductors.
“Uasers can produce an ultrasonic version of acoustical feedback
– an ultrasonic howl similar to the squeal created when a microphone
is placed too close to a speaker,” Weaver said. “By slowly
changing the temperature while monitoring the ultrasonic feedback frequency,
we could precisely measure the phase change in various materials.”
Weaver will describe the uaser and present his team’s latest experiments
at the annual meeting of the Acoustical Society of America, to be held
at the Rhode Island Convention Center in Providence, June 5-9.
The work was funded in part by the National Science Foundation.
To reach Richard Weaver, call 217-333-3656; e-mail: firstname.lastname@example.org.