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Sound wave laser

  1. Dec 17, 2007 #1
    Ok, so recently I've moved on to sound waves in my high school class. I was wondering if sound waves could be harnessed for demolation with accuracy?

    I was thinking the sound would have to move in a linear vibrational path, without dispersing (making a cone shape), is this possible?
  2. jcsd
  3. Dec 17, 2007 #2


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    Laser behavior requires something called a "population inversion." In other words, you need to somehow pump a medium with energy in such a way to create an abnormally large population of energized atoms. When a single photon of light comes near one of these excited atoms, it stimulates it to release its energy in a coherent fashion, and the strength of the light beam grows. This is why lasers are so named: light amplification by stimulated emission of radiation.

    In order to have a "sound laser," you would need some medium which can emit sound, and can be pumped with energy in such a way to be excited, ready to produce sound. You'd also need this medium to respond to a passing mechanical vibration by releasing its excited-state energy in a coherent fashion.

    The only media I can think of that would be a decent place to start would be the pezioelectric crystals. These crystals flex when a voltage is applied across them. Electricity could be used to pump the medium, while the release of flexure would produce sound. One problem is that most pezioelectric crystals have resonant frequencies far, far, far too large to be heard. Stimulated emission may be performed by simple resonance -- when one crystal of an identical pair vibrates, it will induce a similar vibration on the other.

    I wouldn't write off a "sound laser" as pure science fiction, but I think it'd be pretty hard to build one. We're lucky with lasers, since we don't actually have to "build" the resonators. We just select gases whose atoms or molecules have the right properties, and we instantly have billions and billions of individual "resonators." To make a "sound laser," though, we'd have to manufacture each resonator to exacting tolerances.

    - Warren
  4. Dec 17, 2007 #3
    Why so exacting? The cavity provides the precision, in fact it's good to have gain over a wide spectrum. Would a stack of hand-held megaphones in an echoey bathroom qualify as a sound laser?

    But I don't see any point to it unless you can find a much simpler gain medium: with megaphones it would be easier to just hard wire a signal generator immediately to them. Maybe something akin to dominoes (I've wondered whether an evenly/unstably distributed dust acts as a gain medium for gravitational waves). With individual atoms we can't just command them to emit light coherently, hence we have to pump them inside a resonator until they feedback constructively.
  5. Dec 17, 2007 #4

    Claude Bile

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    A megaphone under the effects of feedback could technically be regarded as a sound laser, since one obtains a narrow spectral output defined by the characteristics of the cavity (which in this case the "cavity", is the feedback circuit).

  6. Dec 17, 2007 #5
    that's fascinating. thanks a lot everyone, I'm going to pursue this at best I can. The idea originally struck me as so odd i had to investigate, but i think it would make a nice research topic.
  7. Dec 17, 2007 #6


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    Leaving aside the laser part - you can of course do quite a lot of damage with a sound wave.
    Since a sound wave is just a change in air pressure you could argue that any air blast explosion is a sound wave and something like a shaped charged is a focussed sound.
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