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Do 2 laser beams interfere?

  1. Nov 6, 2013 #1
    I have a question about this old (closed) Thead about the quote:

    "....but also two separate very low intensity laser beams have been sent through single slits to a common detector and a diffraction pattern resulted. The intensity was so low that the probability of a (semi-classical) photon being between the slits and the screen was close to zero." (from Oz)

    I suppose two lasers don't each emit a photon at the same time. So if one photon is emitted by one laser (and not by the other laser) with which wave does the photon interfere?
  2. jcsd
  3. Nov 6, 2013 #2


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    Staff: Mentor

    My understanding is that in such an experiment, the two lasers have to be coupled or "locked" to each other in such a way that there is no information about which laser any individual photon comes from. This makes it analgous to a double-slit experiment with a single laser as a source, in which there is no information about which slit any individual photon passes through.
  4. Nov 7, 2013 #3
    Two lasers must be synchronizes to be sure that the photons has the same phase. But can lasers be locked that both also emit a photon at the same time?
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