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Can you Suspend a Light Beam?

  1. Apr 26, 2008 #1
    I was wondering if you could put a laser beam into a set of mirrors and then once you turn the laser off, have the laser still bouncing off the mirrors. The only way I could think of was if you used a beam splitter like in the diagram.

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  3. Apr 26, 2008 #2
    What you are suggesting could work, but it would be very difficult to align the mirrors welll enough to sustain the light for any long period of time.
    Also it would be much simpler to use two parallel mirrors (easier to align).
    Depending on your application, perhaps an elliptical mirror would work better (although, i don't think thats especially feasible either...)
  4. Apr 26, 2008 #3
    That makes sense.
    What is an elliptical mirror?
  5. Apr 26, 2008 #4


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    Not really any reason why it can't be done, other than the fact that mirrors don't reflect 100% of the light incident on them, they will alway absorb a little bit of it. The quality of the mirror will dictate how much it reflects/absorbs. Because light is so fast, it will get a lot of bounces very quickly and degrade into nothing in a few microseconds...
  6. Apr 27, 2008 #5


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    .. and I'm assuming you want to suspend a beam of light because it will "look cool." Problem is, it won't work if you can see it. Seeing it would mean photons are bouncing off something and flying into your eyes, a.k.a. more light lost.

    In fact you couldn't really do it in air at all, it would have to be in a vacuum.
  7. Apr 27, 2008 #6
    An elliptical mirror is one that is designed in an elliptical shape --> which is a conic section, or closed curve - like a squished circle. Ellipses have the special property of 2 very elegant focus points, which would make it alot easier to trap light in a region at the same time as having a place to insert it from.
    It would certainly need to be in a vacuum to remain for long periods of time (so as to prevent the light from interacting / getting absorbed by particles in the air).
    Mirrors can't reflect all light anywhere close to 100% efficiently, but to my knowledge, when created for a particular frequency (or small frequency range), mirrors can be made to essentially (though still not quite) 100% efficiency.
    The general conclusion is that keeping light bouncing back and forth in any small, defined region, indefinitely, would be impossible; but with alot of trouble you can keep it contained for increasing periods of time.
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