Sonic laser

sonic laser

The ultrasound equivalent of a laser could lead to important new discoveries in materials science by providing researchers with a non-destructive way to detect even the subtlest of changes, such as phase transitions deep in their samples. Now, researchers at the University of Illinois at Urbana-Champaign and at the University of Missouri-Rolla have built just such an ultrasound analogue of the laser – the uaser, pronounced way-zer.

Light amplification by stimulated emission of radiation devices, lasers, are well known, but a sonic analogue had until now not been developed. Richard Weaver and his colleagues set out to change that and to develop a device that would induce ultrasound amplification by stimulated emission of radiation to produce coherent ultrasonic waves of a single frequency. “A sonic laser has been possible for some time now,” Weaver told us, “our method could have been done earlier. I tend to think it wasn’t for two reasons: first no-one saw an application and second few people are expert at both laser physics and ultrasonics.”


7 thoughts on “Sonic laser”

  1. Comment from Dr Richard Weaver via email:

    Hi David –

    I’d not call it a laser any more than I’d call a flute or a violin string a laser. All three of those take a noisy input and, by resonance in the object, modify the input to match the resonance.

    One level even more simple is a bell, or a piano, in which the input is fixed, and the object just responds with its natural frequency.

    A laser, however, causes numerous noisy inputs to synchronize to the resonances of the object. The key feature is that so many ostensibly independent sources work in cahoots, not just one. They furthermore do it in a manner that enhances rate of energy output above that that the many sources could manage if acting independently.

    This aluminum bar, and the violin string, and the flute, could be thought of as single-atom lasers, but they are way less special that a laser that makes so many inputs act together.

  2. It may very well have been…in fact, I’d be surprised if it didn’t have some kind of superior structural properties, after all the crystals used for electromagnetic (visible, IR etc) lasers do.


  3. One more follow up and then I will leave this alone. Again, the demo I saw was a long time ago and I can’t find any notes that I took that evening. The more I have thought about it the more I think I am leaving something out. Think the bar of aluminum had been zone refined and was a single crystal of aluminum which means it was not your every day garden variety of 6061 aluminum. Seems like it might have been pure aluminum, but am unsure of that.


  4. As I recall, it was a pure tone. His explanation was that the aluminum bar worked just like a light laser and that by rubbing it he was inputting noise into the bar and that it was reflecting off the ends of the bar just like a light laser reflected off the mirrors at the end of their housings. He indicated the length was important in determining the frequency that was produced. Never heard of it again, just the demo that one night.


  5. Greg, thanks for sonic comment Greg. Do you happen to know if the middle C being produced was a pure tone or whether it had harmonics. Although directionality is a key aspect of a laser beam, the output also has to be coherent. It’s possible that this wasn’t strictly speaking a sonic laser effect, but obviously I don’t know unless you can provide additional details.

    Fascinating thought nevertheless, I wonder if the NASA demo led on to anything.


  6. The comment about a sound laser not being possible until recently is wrong. I saw a demo put on by a NASA educator at a SME (Society of Manufacturing) meeting almost 15 years ago showing one. The man pulled a length of aluminum rod 3~4 feet long and 1~1.5″ Dia from a protective case and rubbed it with a cloth of some type. He said the ends of the bar were very finely machined square and parallel and then polished. As he pointed the bar around the room you could here a middle “C” note as I recall. It was very directional and very powerful, and a fabulous demo of the laser principle.

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