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Laser interference

  1. Jan 20, 2007 #1
    Laser emits due to the stimulated emission.
    As the photons produce in this process are coherent, I would like to ask why they won't undergo interference and produce alternating bright and dark light when they just come out from the laser source.

  2. jcsd
  3. Jan 20, 2007 #2


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    Gold Member

    You answered the question yourself - because of the fact that they're coherent they all have the same phase everywhere - waves only interfere when they have different phases.
  4. Jan 21, 2007 #3
    In some cases there are oscillations, see http://en.wikipedia.org/wiki/Transverse_mode. The width of the laser medium will set some limit on how collimated the beam can be, which is a diffractive effect. The transverse modes have smoothly-sloped edges, so you don't see the classic diffraction rings you would see if you sent the beam through a hard-edged pinhole.
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