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Homework Help: Diffraction through a ring aparture

  1. Oct 31, 2009 #1
    1. The problem statement, all variables and given/known data

    1.compute the diffraction pattern through a ring aparture, internal radius a, external radius b, wave length lambda. the incoming wave is a monochromatic, plane wave, vertical to the ring plane.
    2.how will the diffraction expression change when a->b?
    3.near the aparture a narrow lens with f=10 cm' lambda=1micrometer, a=2mm, b=2.05mm.
    draw the intensity i the lens focus plane, according to the first computation, and themn according to the second.

    2. Relevant equations

    fernahufer diffraction equations.

    3. The attempt at a solution
    I did article 1 and got an electrical field with 2 bessel functions, one minus the other. I dont really know how to do 2,3.
  2. jcsd
  3. Nov 1, 2009 #2
    Well, your solution to 1 sounds good because the solution to a circular aperture (easily found on the internet) involves a bessel function and you should be able to do a superposition to get a disk. For 2 you should be able to just take a limit of you equation from part 1 as a goes to b. Otherwise you could solve a ring aperture of delta function width.
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