Turning a circle into a square

1. Dec 16, 2009

dm9292

Question
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.

Solution
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. Dec 16, 2009

chaoseverlasting

I couldnt really understand the problem. Could you elaborate upon it? What do you mean by a cross in a mask?

3. Dec 17, 2009

dm9292

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.

4. Dec 17, 2009

gabbagabbahey

Whenever you have light passing through a thin aperture, diffusion should immediately come to mind.

5. Dec 17, 2009

dm9292

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: