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I am trying to use a beam splitter to produce a reference beam that is separate from the subject beam. I find that when I use a simple thin-glass 50t/50r splitter I get gross interference stripes all across the hologram - no matter whether I use the Transmitted or the reflected beam as my reference beam. Since this is a piece of glass, the interference stripes make sense, but it makes such beam splitters useless.

So I tried two different prism beam splitters, a cubic and a pentagonal and both of them produced a splatter of "freckels" across the hologram. It took a process of elimination to figure that it was the beam splitters doing that, but eliminating beam splitters cleared up the problem.

Question: can anyone suggest what I am doing wrong or how I might solve this. Thanks for any clues.

It's possible that your cube beamsplitters may have some kind of structure within them, ie cracks, bubbles etc. This would cause scattering and cause your freckles.
I used a variable neutral density filter ( https://www.thorlabs.com/newgrouppage9. ... up_id=1393 ) simply because the studio I started in, Richmond Studios, London) used them back in 1982. Today, I think, most holographers use a cube splitter ( https://www.thorlabs.com/newgrouppage9. ... oup_id=754 ). The link I posted is for a non-polarising splitter, which is probably easier for a beginner to use. Polarising beamsplitters require additional components and may be harder to use.

Din, thank you very much. I am encouraged that you suspect the inner planes of the cube as I do. The cubes I am using were very inexpensive. I have another inexpensive one arriving in a few days which I will test, but if I see the same problem, I will purchase a good one since, for my project, a good beam splitter is essential. Everything else is working fine - it's the last problem I have.

Thanks again for the link.

Can’t use thin glass as a splitter, needs to be thicker as the outputs need to be separated more, sounds like there are too close to each other ( like stepping on each other) causing interference bands… try a1/4” plate..

If you feed your reference beam into a spatial filter, the simple thin plate beamsplitter may work as the reflected beam would be focused outside the pinhole.