In article , DoN. Nichols
wrote:

2) Something to divert a laser beam (coming in through the
slot) into one of three paths. Or maybe even all three
at once to set up a complex set of beams which recombine
to allow comparison of phase after being acted on by
things in all three paths.

That rang a bell... Betcha it's used for making holograms.

djb

--
"The thing about saying the wrong words is that A, I don't notice it, and B,
sometimes orange water gibbon bucket and plastic." -- Mr. Burrows