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Derivation help

  1. Sep 28, 2009 #1
    does anyone know how to derive this equation regarding the Michelson interferometer:

    d_m = (m[lambda])/2

    where d_m is the physical distance of a micrometer division, m is the number of fringes that crosses a screen given some d_m and lambda is the wavelength of the laser used to create the interference pattern.

    I understand that the path difference divided by the wavelength is responsible for the number of fringes that pass by a certain mark, but I don't understand where the 2 comes from. Can someone help me please?
     
  2. jcsd
  3. Sep 28, 2009 #2
    oh hehe never mind.


    as it turns out because the path difference divided by the wavelength is number of fringes that pass I can set up a diagram to evaluate the problem.

    Quite simply, the change in distance for the interferometer which has an arm that changes length is just 2L - 2(L-d_m) which gets 2d_m as the change in distance. Thus:

    2d_m = m[lambda]

    or

    d_m = (m[lambda])/2


    how silly of me
     
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