CCD

One way to improve beam coherance is to add a collimator which is essentially a Galileo telescope in reverse. The beam spreads a little but no further. Then your black washer stack size or fiber can be reduced to one of the desired size in theory.

Visible laser pointers are under $20 complete which is inexpensive compared to the desired 0.0001" function enhancement. And that's retail -- you should be able to get them for half. Red light may be more annoying than IR but it should enable improved resolution since the wavelengths are shorter. Higher resolution can be had the closer you get to UV but the more expensive parts get.

Back in 1970 I saw an ad in Scientific American for a Hewlett-Packard precision measuring device that used two laser frequencies to get extra precision. They didn't say why and I didn't ask but maybe it was to reduce backscatter errors since each frequency would have a different refraction angle.

Fiber optical cable is now used in some businesses for computer networks instead of coaxial cable. The installers have simple kits for polishing the ends before hook-up. You might be able to get one of them to give a supplier if Edmund's Optical division isn't adequate.