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Homework Help: Two identical diffraction gratings

  1. Apr 21, 2015 #1
    1. The problem statement, all variables and given/known data
    We shine a laser light on two identical diffraction gratings as shown in picture. Captureg.PNG
    Calculate ##x##, if in Fraunhofer diffraction image the seventh peak is missing.
    2. Relevant equations

    3. The attempt at a solution
    No idea actually. I know how to do this with one diffraction grating.

    For one grating all one has to do is compute a product of Fourier transformations of aperture function and sum of delta functions.
    For one grating, the result is ##u_p=C\frac{\sin(k_xa)}{k_xa}\frac{\sin(k_xNa)}{\sin(k_xa)}##.

    But I have no idea what to do with two diffraction gratings? Is it simply a product of both where one is shifted for ##x## ?
  2. jcsd
  3. Apr 23, 2015 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    What would you take as:
    - the separation of the gratings?
    - the thickness of the gratings?
    ... try redrawing the diagram in a more realistic representation.

    There is a clue in the description involving the Fraunhoffer diffraction image... why would there be a peak missing?
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