OK, no more grumbling about software!
So, been waiting for the optical flats to show up. They finally did, along with the monochromatic light source, sort of.
As green laser diodes are still hard to make, most green lasers are diode pumped 808nm->1064nm->532nm sources. Meaning they are very much monochromatic, with a known wavelength. Asian makers are selling them very cheap. Ordered a couple $20 'fat beam' 'dance' lasers. Ordered a green, and a 405nm also. The 405 is out for this projects, as expected the optical spectrometer shows it's not very narrow. The green is very narrow.
Power meter showed the green to be 112mW output. That's actually quite a bit scary, in a small laser, for $20. Part of that may be 1064nm and really bad for the eyes! Still waiting for the IR filters for this thing. However, curiosity got me and I pulled the front lens, and fitted a ping pong ball diffuser to give it a test run.
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Very nice green source. The laser speckle is very brilliant. (Yes it makes the cell phone camera puke! )
Setting one flat on the other is a good sanity check, and that looks pretty good. (Again the cell phone camera pukes, and the auto white balance turns what is a very very green image to a color image!!!)
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Checking the cylinder square shows a pretty consistent high band dead center of the support surface. However, it's impossible to photograph with the phone. A white light look shows the high band, but it's hard to pick out the deviation as you approach the outside edge. It's maybe 4 bands of 532nm light. IIRC, that is 10 millionths per band, or maybe about 40 millionths curve across the support face. It looks very even overall, so some mild lapping may clean that up. Just need to start making and lapping in the lapping plates.