The question:

Is my basement sufficiently vibration-free as to make holography feasible?

The nominal procedure to answer this question is to build an interferometer.

I started with my old helium neon laser.

My mirror mounts are steel straps, like are used to reinforce doors, with a pivot on one end and a screw on the other, rubber banded to bricks. The mirrors are then stuck to the straps with magnets. The screw is an azimuth adjustment, and rotate the brick for angle.

My beam splitter mount is another steel strap screwed to a piece of 2 by 6. I sometimes put a brick on top of the 2 by 6. It unfortinately dosn't have an angle adjustment. I've been ignoring that problem for now.

My lens, to expand the beam so the pattern is large enough to see, is an old C mount video camera lens. This is less than optimal, a single element lens would be better.

I then assembled the interferometer on the concrete slab floor in my basement. It was pretty stable. I could jump up and down in the walkway leading to the basement about 6 feet away from it, and not move the fringes.

Then I switched to the blue argon laser. And there was much gnashing of teeth. The setup which was good enough for red seriously sucks for blue.

The mirror mount bricks could wobble (They aren't quite square, and my floor isn't quite flat). So I put 3 little rubber feet on them, thinking three points would be more stable. While it felt more stable, the rubber was too flexible, so it was really even more wobbly. So I tried 3 little Plexiglas feet, thinking its less flexible than rubber. No joy, still too flexible.

So I went back to the HeNe laser, then set the argon laser right beside it and ran all the cooling blowers, so see if the vibration was coming from the laser. That revealed that the air flow was... not helping. So I made some cardboard baffles for the air, and a vibration isolation platform for the laser power supply and blower out of a piece of particle board sitting on top of a trash bag of packaroni. The cardboard air baffles helped the most, but I kept the power supply vibration isolation anyway.

So now, the argon laser could happily sit beside the red interferometer and not cause problems.

So back to the argon laser. I managed to see fringes as they whipped past this time...

So I tried one more isolation table. I had a piece of Formica counter top laying around. So I balanced it on three pieces of closed cell foam. Then I put the bricks etc. on top of it. The laser was about 2 feet away, sitting on its own bricks (to get it high enough to get above the isolation table) behind a cardboard draft shield with an approximately beam sized hole in it.

Finally, the fringes were stable. It was in fact more stable to my jumping on the floor than the red one (directly on the floor).

Which revealed another interesting behavior. The argon laser goes multi-mode real fast as you increase the power. Its rated for 4mw at its end of life, and was measured at 13mw. Problem is that it goes multi-mode just barely above idle, that 13mw is completely unavailable for holography. So, if your interferometer is just not interfering, turn down your power to idle.

The other not quite intuitive thing is that vibration isn't a problem until the beam splitter. (Or at least my intuition failed...) The laser can move relative to the optics. As the laser moves, the interference pattern looks like moving a light shining through a set of Venetian blinds. That makes vibration of the laser, due to cooling etc. much less of an issue. Make sure any streams of air heading for the optics are blocked though...

The real solution

A proper optical table is a monstrosity at least 8 inches thick (the table must not bend, think I-beam physics.) , sitting on buckets of sand and inner tubes. The top and bottom of the table are quarter inch thick steel. The center of the table is honeycomb aluminum, or perhaps honeycomb PVC, or maybe solid stone. They weigh multiple hundreds to thousands of pounds, and are a serious investment. The optics mounts are more chunks of steel, held to the table either with screws or serious magnets.

So, my setup is in fact a toy, and an extremely poor one at that. However, I'm not prepared to spend that much money on this project right now, and it does work.

The budget will be reevaluated after some holograms come out. :-)