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Homework Help: Fabry-Perot Etalon

  1. Mar 10, 2009 #1
    1. The problem statement, all variables and given/known data
    A certain spectral line is known to consist of two equally intense components
    with a wavenumber separation less than 20 m^-1: The Fabry-Perot fringes
    produced by this line are photographed, using a plate separation of 25 mm. The
    diameters of the smallest rings are found to be, in mm :
    1:82; 3:30; 4:84; 5:57; 6:60; 7:15:
    Explain why this experiment does not allow the wavenumber separation to be determined uniquely, but gives two possible values. What are they? Suggest a further experiment
    which could be carried out to resolve the ambiguity.

    2. Relevant equations
    Wavenumber FSR=1/2nd

    3. The attempt at a solution

    So I think this has something to do with the free spectral range? If you work that out with the above equation, assuming the etalon is in air, you get 20m^01. So as the wavenumber separation is less than this, fringes from the two different wavenumbers will overlap. But then I don't know how to get the two possible answers.

    Any help? Please?
  2. jcsd
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