Dear Zemax community,

I am building upon your 'How to design a Gaussian to Top Hat beam shaper' tutorial. I additionally want the top hat to be collimated over a 30cm propagation distance.

I setup the system with two aspheres and an optimization macro that squares my beam (REAY operand, as in the tutorial) and subsequently collimates it with the RANG operand (target is 0 angle). However, it fails to maintain the top hat shape and collimation over the propagation distance. Am I using the wrong operand to collimate, or should I use the constraints with two dummy surfaces (at a distance of 150mm (MIDPOINT) and 300mm)? 

Any suggestions are welcome and appreciated.

Thank you very much, Paul