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Researchers Build An Ultrasound Version Of The
Laser
Champaign, IL, June 8: Researchers at the
University of Illinois at Urbana-Champaign and at the University of Missouri at
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 modern materials.
"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 Missouri
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 frequencies.
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.
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