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Double Slit Question

  1. Aug 29, 2009 #1
    I have a question about Young's Light-double slit experiment, is there a minimum ratio between the intensity of the light and the size of the slit or the distance in between the slits to alter the results? For example, if a wall has two open doors into the same empty, standard room and a photon is fired from the center of a wall into the right open doorway, will it still interfere with itself in a manner similar to the standard model for the experiment?

  2. jcsd
  3. Aug 29, 2009 #2
    The slits have to be not too much larger than the wavelength of the light. Usually the experiment is done with light of a particular wavelength within the visible spectrum (somewhere between 400 and 750 nanometers). The separation between slits also has to be small. If you make two small holes let's say 1mm wide by hand on a piece of cardboard and try to see interference you'll be disapointed. In order to do the experiment you don't need to shoot one photon at a time. You can illuminate the slits with a laser pointer which will give you a single wavelenght. You could search the web to see what is the best way to make the small slits. I think you might be able to make them by cutting two small lines with a razor blade on a painted microscope slide. With respect to the intensity of the light, it does not affect the shape of the interference pattern. Only the wavelength, slit size and separation affect it. You might be able to find more information in Wikipedia.
  4. Aug 30, 2009 #3


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    Staff: Mentor

    It depends on how you produce the photon.

    If you use a light source that radiates a broad cone of light that covers both doors, you'll get an interference pattern, at least in principle. Actually observing the pattern is difficult because for large apertures the spacing between maxima and minima becomes very small. If you then decrease the intensity of the source so it emits only one photon at a time, in a random direction inside the cone, you still get interference.

    On the other hand, if you use a source that emits a narrow beam like a laser and aim it through the center of one door, you obviously won't get any interference. If you decrease the intensity so the beam contains only one photon at a time, there' still no interference.
  5. Aug 30, 2009 #4
    I thought one of the complexities of the issue is that a single photon shot through one hole of a double slit results in a hit pattern that over time reflects a pattern of self interference?
  6. Sep 2, 2009 #5
    Here's a video of a double slit experiment with a laser pointer. You can find anything on Youtube.

    Last edited by a moderator: Sep 25, 2014
  7. Sep 2, 2009 #6

    Doc Al

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    Staff: Mentor

    Again, as jtbell explained, it depends on how you produce the photons. If your beam covers both slits, then you'll get an interference pattern (eventually) even if you turn down the intensity so that only a single photon is passing through the slits at any time.
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