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Solid rubber does not isolate. Also, the isolation would need to be under the concrete slab, not under the steel, so that the weight of the concrete was above the isolation. Weight below the isolation does not help. The steel needs to be fully supported by the concrete. A layer of concrete patching ...

If the concrete table slab touches the steel frame anywhere, the isolation from the tubes under it will be lost.

The table being in a closed room is not good enough for the air stability you want. One needs to enclose the optical system in as small an enclosure as practical, with as many baffle cards inside as possible. You will be amazed at how much this simple thing improves stability.

Looks like air motion to me. I would build an enclosure for the interferometer out of cardboard boxes, with only a hole to allow the beam to enter and another hole to observe the fringes (but if possible, put a piece of glass over the observation hole).

I'd suggest looking at your dehydration technique. Most use three baths: 50%, 100% and a final 100% IPA, all hot, and all for much longer time than you mentioned. The time in the baths is important, as it takes time for those molecules to do their thing. It takes a few minutes for the water molecule...

You're right Dave. One CAN make the hologram with any divergence in the reference, and an image WILL play back with the unmatched conjugate, but whether the distortions and swing are acceptable depends on whether you want to sell it or not. If you're Rudy Berkhout, you work with those issues and can...

Spherical mirrors suffer just as much as parabolic mirrors when the input beam is tilted off axis. The parabolic mirror gives a collimated output, while the spherical mirror will never do that. Always use parabolic (telescope) mirrors. Be careful to not get one that has a center spot permanently etc...

What difficulties have you had with paint? A solution may be to seal the hologram with epoxy or RTV (like Ron & Bernadette Olson use), and a piece of glass. Then paint the back. Use a piece of smoked or black glass and you may not need to paint.

Here's a good technique: https://holographyforum.org/forum/viewt ... TReh7I2Ueg

Consider trying things you can find around the house for free. Find an old camera, bash it apart, and harvest some lenses from that. Try passing the light through areas on a wine glass stem. Be careful with the back reflections! Glass marbles? Glass door knobs? An old projection TV? Lots of things i...