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Homework Help: Turning a circle into a square

  1. Dec 16, 2009 #1
    How is a circle of light turned into a square of light using a mask with a cross. This isn't actually my homework but a challenge question.

    I really have no idea I've looked around on the net and looked in the library but I can't find anything relevant. I don't actually understand how the cross manipulates the light to produce a square. I must ask is it even possible using light or do the same limitations experienced when trying to do this geometrically arise?
  2. jcsd
  3. Dec 16, 2009 #2
    I couldnt really understand the problem. Could you elaborate upon it? What do you mean by a cross in a mask?
  4. Dec 17, 2009 #3
    Well by a cross in a mask I mean you shine light through a square shaped image and then you have metal mask which has a thin cross in it, this is placed after the square image. By doing this the square is now turned into a circle.
  5. Dec 17, 2009 #4


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    Whenever you have light passing through a thin aperture, diffusion should immediately come to mind.
  6. Dec 17, 2009 #5
    These are the hints i got, but i am not sure where to go from there:

    Say your laser has a Gaussian beam profile and you shine it through a hole to yield a Gaussian-Bessel function:

    How does a Fourier transform of the waveform look in 1D (ie taking an arbitrary cross-section slice of the 3D profile)?

    From the transform, how do you think you create a 2D square out of it?

    I'm still trying understand this and if anyone can help it would be much appreciated.
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