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Homework Help: Diffraction Grating Angles

  1. Jan 2, 2012 #1
    1. The problem statement, all variables and given/known data

    I'm choosing an angle for a diffraction grating such that a laser of particular wavelength λ is retroreflected (reflected back along incident path).

    2. Relevant equations
    If you have a better way than using the equation below, feel free to explain. The book that I'm looking through treats the blazed diffraction grating as a set of N slits. This results in the equation


    where β=(kb/2)sin(θ) and α=(ka/2)sin(θ) with b=length of slit and a=distance between center of two adjacent slits

    k is the wavenumber(I think).

    3. The attempt at a solution
    What I'm looking for is a kick in the right direction. I'm not sure how this equation helps me. I don't know how to use k and and I don't really know a or b (although I could calculate them). I'm not sure how N^2 comes into play since I don't know the total number of slits on the grating. Also I don't know why the total number of slits should play much of a role when the laser is incident on only a tiny portion of the grating. I think there is something fundamental that I'm not understanding. Obviously I want the intensity to be maximized along retroreflected path. Any help would be great. Thank you.

    Last edited: Jan 2, 2012
  2. jcsd
  3. Jan 2, 2012 #2
    Does anyone know how to determine the angle at which to place a diffraction grating such that a particular wavelength of light is reflected back along the path of incidence? Do I need to rephrase the question? Any help is much appreciated.
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