Analytically transform a spherical wave into a planar one Is it possible to transform a light spherical wave front or another wave front with a known behaviour into a planar one?
Say I have the position of a point light source, and I can approximate it by an isotropic spherical model (just as an example), what kind of operations do I need to do to make it a planar wave. More specifically, if I take a plane perpendicular to the light axis from an unknown distance to the light, I want to simulate a constant lighting on that plane.
I know a spherical wave can be transformed to a planar (or almost planar) using different optics, however, I am not sure how/if this can be done analitically. Is it at all possible?
 A: That's what a lens does.  So if you take a look at the equations governing, say, a lens placed its focal length away from a point source, that will show you how a spherical wave emanating from the point source is transformed into an outgoing plane wave. 
I hope that's what you're asking, since "mathematically transform" doesn't have any real meaning.
A: To add to Carl Witthoff's answer: a plane wave won't simply become spherical just by propagating. One piece of background you seem to be lacking is this: plane waves are eigenmodes of freespace (or of any homogeneous medium), meaning they do not change their form by propagation (aside from taking on a phase delay) in a homogeneous medium. So, if they are going to change their form in any way aside from simply being delayed, you have to have a specific piece of hardware comprising a non-homogeneous medium in mind to do the transformation. So, as Carl says, you need to imagine a specific lens and work out the transformation it makes.
Otherwise, if you're willing to accept a Gaussian beam with a huge waist parameter (see Wiki page "Gaussian Beam") as an approximation to a plane wave, you can let it propagate a huge distance, much greater than the Rayleigh distance for the Gaussian beam. Its wavefronts will then have a radius of curvature roughly equal to the propagated distance. 
