Richard Clark, KB7QHC wrote:
"That is, Gaussian being wholly divorced from matters of current and
more related to shape distribution?"

Yes. Put your search engine to work on: "Radio & Coherent Techniques".
Probably the first item to pop up will be: Scots_Guide/RadCom/introhtml.
Part 11 of this is "Designing Quasi Optical Circuits". First example in
this is a free space "Gaussian Beam" radiated from the enf of a glass
fiber. Lots of pages and lots of stuff in those pages.

Best regards, Richard Harrison, KB5WZI