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I Order Maxima under the Fraunhofer Envelope

  1. Aug 5, 2017 #1
    Let's say we are using a spectrometer to observe the order spectrum of mercury, a polychromatic source.
    Each order contains a an array of colour bands.
    In the case of the following image: http://imgur.com/a/bnm9r , I was wondering if each Fraunhofer envelope represented one order, (m = 1 , 2 , 3 ...) or if each line under the envelopes represent each order, where the central line in the first envelope is the central maxima.

    Also, the following picture is the order spectrum of hydrogen http://imgur.com/a/DkrJC
    Why is it that after each order, the spectral lines separate further away from each other?
    Last edited by a moderator: Aug 6, 2017
  2. jcsd
  3. Aug 6, 2017 #2


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    In a double interference with finite width of the slits, it's useful to distinguish between diffraction order and interference order. The reason is that the intensity pattern as seen in the screen is a product between the single diffraction pattern from a slit with non-zero width and the double slit (but zero slit width) interference pattern. Some books called this product rule the array theorem. The envelope is the diffraction pattern from a single slit, therefore the peaks of the envelope correspond to a given diffraction order.
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