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Possible to make 2 beams of light cancel?

  1. May 23, 2008 #1
    Last night, I was doing some really cool stuff with light interference, like the double split experiment and such. so, then i started wondering, is it possible to make 2 beams of light from different sources cancel each other out? [see attachment (gray are represents steam or something to make the beams visible)] i looked on the internet quite a bit and couldn't find anything :/

    Attached Files:

  2. jcsd
  3. May 23, 2008 #2
    Yes, you could theoretically make them cancel using wave superposition. But it would be very hard to do.
  4. May 24, 2008 #3


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    Probably, if they have exactly the same frequency, and you align them perfectly, it would be possible to cancel them in one direction. But I suppose you would have constructive interference in another direction (something with energy conservation).
  5. May 24, 2008 #4
    ok, thats what i thought... but, does anyone know of any experiments that have been done that show this? (preferably on the internet so that i can look them up)
  6. May 24, 2008 #5


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    CompuChip is right, if the beams cancel in some place(s), they must constructively interfere somewhere else in order to conserve energy.

    I never heard of experiments with light beams whose purpose was to confirm energy conservation. But we can look at specific examples, like the one depicted in Post #1, and show why we can't have cancellation everywhere.

    Looking at the picture in Post #1, suppose there is a point within the beam-overlap where we have cancellation. That is, there is a 180 phase difference between the 2 beams at that point.

    Now all you have to do is move 1/2 wavelength along one of the beams, so that the phase will change by 180 degrees for that beam. But for the other beam, you are moving across the beam and so there is no phase change for this second beam.

    The net phase change is then 180 degrees. Coupled with the initial 180 degree phase difference, there is zero phase difference (i.e. complete constructive interference) in this 2nd location.


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