1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Homework Helper
    Gold Member

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook