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Homework Help: Diffraction of a circular aperture

  1. Mar 4, 2010 #1
    1. The problem statement, all variables and given/known data
    A collimated laser beam ( λ=600 nm) having an intensity I=10 W/m2 is incident
    perpendicularly on an opaque screen containing a circular hole with diameter
    D=3.6 mm. Calculate the intensity at a point on the central axis that is distanced
    180 cm from the screen.

    2. Relevant equations


    3. The attempt at a solution

    firstly I am confused if i should treat this as Fraunhofer or Fresnel diffraction. I know that for a circular aperture it will form an airy disk, but that will leave the bessel function = 0, which means the resulting intensity is zero. (that would make sense if the center is dark, ut it should be bright.

    I really think I am missing something simple here. please help.
  2. jcsd
  3. Mar 5, 2010 #2


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    Homework Helper

    It is true that the J1(x) Bessel function is zero at x=0, but J1(x)/x has a finite limit.

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