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  • Ultrasound Laser Analog Built
Jun 2006
CHAMPAIGN, Ill., June 13, 2006 -- By using sound instead of light, researchers have mimicked the essential nature of a laser by creating its ultrasound analog. 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, its creators said.
Richard Weaver, a professor of theoretical and applied mechanics at the University of Illinois, and colleagues at Illinois and the University of Missouri-Rolla have built an ultrasound analog of the laser. (Photo: L. Brian Stauffer)

“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 the University of Illinois.

To make a uaser, Weaver, Illinois research associate Oleg Lobkis and University of Missouri-Rolla 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, Weaver said, 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, Weaver said. With their longer wavelengths and more convenient frequencies, they could prove helpful 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, he said.

“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 described the uaser and presented his team’s latest experiments at the annual meeting of the Acoustical Society of America, held June 5-9 at the Rhode Island Convention Center in Providence. The work was funded in part by the National Science Foundation.

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A physical variable that is proportionally similar to another variable over a specified range. An analog recording contains data that is similar to the source.
A metal, alloy or compound that loses its electrical resistance at temperatures below a certain transition temperature referred to as Tc. High-temperature superconductors occur near 130 K, while low-temperature superconductors have Tc in the range of 4 to 18 K.
1. An undulation or vibration; a form of movement by which all radiant energy of the electromagnetic spectrum is estimated to travel. 2. A type of surface defect, usually due to improper polishing.
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