An ultrasound analog version of a laser could one day be used for medical diagnostics. Researchers at the University of Missouri–Rolla and the University of Illinois at Urbana-Champaign developed the device.
Called a uaser— 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 the University of Illinois.
The uaser was made by mounting a number of piezoelectric autooscillators 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. 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,” says Weaver. “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.”