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Laser Beam Destructive Interference

  1. Jan 19, 2009 #1
    If two lasers are pointed emitting end to emitting end in a vacuum (for lowest divergence), and emit 2 beams of light 180 out of phase, could both beams destructively interfere completely (no light coming from either emitting end after the beams converge)? If the experiment was done under conditions where some of the laser light could scatter, would a "shadow" propagate from the point of convergence to the emitting ends of the lasers (assuming the lasers are far enough apart where this can be reasonably detected)? Where would the energy of the beam go (heat?), assuming the lasers continue to function after the beams converge? Would beams travel into the emitting end of the the opposing laser and interfere with the gain medium?
  2. jcsd
  3. Jan 27, 2009 #2
    If two beams are directed in opposite directions and have the same amplitude, in the gap between the lasers' ends will be a standing wave, like in a resonator. In this case the 180 degree phase shift can be established only for points in this gap, standing apart on a half wavelength. For other points it will change between 0 and 180. So, no destruction of the wave picture in the gap, but lasers may be destroyed.
  4. Jan 28, 2009 #3

    Andy Resnick

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    Unless the two lasers were mutually coherent, no interference would occur. A simpler experiment is to use a laser with a very long coherence length, split the beam and create a ring cavity. In this case, there is a standing wave pattern. Even so, it's not clear what would happen- some of the light would re-enter the laser cavity and alter the lasing characteristics.
  5. Jan 28, 2009 #4
  6. Jan 29, 2009 #5
    Right. Destructive interference does not imply that the waves cease to propagate.
    This is important and a common misconception.
  7. Feb 17, 2011 #6
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