K7ITM wrote:
At least, that is what I observe; perhaps I'm
not observing closely enough. ... but sensibly there is no effect on
one beam from the presence of the other.

It is obviously difficult to get two light beams
traveling in a collinear path. That's the reason
you have not observed wave interaction. If it
were possible to get two coherent laser beams
of light traveling in exactly the same path in
the same direction, what would be the result?

Two coherent beams of laser light of equal amplitude
and opposite phase traveling forever in exactly the
same path. What would happen under those ideal
conditions?

Getting waves collinear in a transmission line is
easy.
--
73, Cecil http://www.w5dxp.com