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Single photon - how do they do this?

  1. Mar 31, 2005 #1
    Not sure if this is the right forum for this - if not please correct me. One thing I've always wondered - How do researchers set up experiments - such as the dual slit experiment - to slow down and allow only a SINGLE photon or electron at a time? How do they do this? Especially with photons, how do you allow only a single photon at a time? Can something like this be done outside of an expensive research lab?

  2. jcsd
  3. Mar 31, 2005 #2
    I believe if you shine light on a metal, theres a certain frequency at which an electron is emitted, its speed proportional to the energy of the photon.

    Photons are emitted when electrons travel from high energy states to lower energy states. I'm sure they can control this one also to conduct an experiment with the result.
  4. Apr 1, 2005 #3
    Decreasing the intensity of a light source is equivalent to reducing the number of photons. Low intensity is the key.

    As for an expensive lab, the human eye can detect 5 or more photons at a time. If you gradually decrease the intensity of a source, eventually you will reach a point where half the time you see a flash and half the time you don't (even though you know one occured). This is when you know you are right on the borderline of 5 photons at a time.
  5. Apr 10, 2005 #4
    Is the size of a photon arbitrary?

    Photons are "bundles of light." There is discussion about whether or not light is infinitely divisible, correct? If we don't know that it is by nature particulate, how did we decide the size of these bundles?

    Sorry for all the questions. This is a great topic. Thank you. I have been trying to find information on this for a while, but many authors and teachers seem to prefer it as "not important." :cry:
    Last edited: Apr 10, 2005
  6. Apr 11, 2005 #5
    I haven't gotten as many responses to this as I had imagined so allow me to broaden my question:

    I've been reading a lot about experiments that have been performed with light, the dual slit experiment being one of them. While I believe the results I read about, I'm the type of person that like to try these things for myself. So, how would someone not in a large expensive lab attempt an experiment where the idea is to 'shoot' a single photon at a time? How do the big research labs do it?
  7. Apr 11, 2005 #6


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    Staff: Mentor

    A Google search on "single photon interference" turns up on the first page of hits, links to descriptions of undergraduate lab experiments or demonstrations at Princeton, Harvard and Brown Universities.
  8. Apr 11, 2005 #7
    jtbell, thank you very much for that search tip. Those sites illuminate the matter well, pun thoroughly intended.

    But the question remains. The first site google returns, which is from Harvard, says this in the comments section:

    Isn't it rather sloppy (and possibly false) to say that we are detecting, and therefore emitting, photons one-by-one, when we are really detecting the one-by-one output from the photoelectric effect?
    Last edited: Apr 11, 2005
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