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Light questions (not wave/particle duality!)

  1. Aug 1, 2006 #1
    The classic picture of light is as an electromagnetic wave. In textbooks you get the nice pictures of eletric and magnetic field vectors bound together at right angles, oscillating on into the distance. However, this is a very one dimensional picture. The electric and magnetic fields would only be felt along a line. What happens if you're standing 1 cm away from the axis of propagation? How about 1 nm? Is there a more complex 3-D description of light as a wave? Even if there is a fast decay in field intensity away from the axis and it can be approximated as 1-D, the familiar vector description seems inadequate to me.

    I'm guessing some responses may invoke plane waves, but I am fine with those. It's really only the 1-D description that concerns me. Perhaps, because it's a classical description of a single photon, quantum mechanics must instead be used here, and the 1-D classical description really isn't valid for a single photon? Any other ideas?
  2. jcsd
  3. Aug 2, 2006 #2


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    Staff: Mentor

    See posting #6 in this thread, with its attached diagram. It might help you get a better mental picture of a classical plane electromagnetic wave.
  4. Aug 2, 2006 #3

    Claude Bile

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    You are correct, a light wave must exhibit a finite 'width', EM waves must possess a finite width for continuity reasons. This is also the reason why ray analysis (in optics) fails under certain conditions and why you cannot focus a beam of light into an infinitely small point.

    A more accurate description of a finite light beam are those described using Gaussian Beam analysis. The scalar expression of the fields I find digestible, but the vector description is somewhat horrendous (you would need to wade through some literature to find it).

    More info on Gaussian Beams - http://www.rp-photonics.com/gaussian_beams.html

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