Hi Folks, After a general search online, I have not yet found a simple description of refraction in a medium with an inhomogeneous refractive index. For example: if we have a block of glass with a beam of light shining through it, and the block has a gradient in the real part of the refractive index perpendicular to the direction of beam propagation, what will be the angle it exits the block with? I assume the fromula will depend on the gradient and the thickness of the block, but I don't know how. Also an intuitive picture would help me here, the light has different velocities, but favors the faster route right, so why then does it tend towards the values with higher n? Where it is slower! See wiki GRIN lenses. Many thanks!