Beam Splitter Problems

Holography related topics.
John Howard
Posts: 25
Joined: Fri Jul 06, 2018 11:36 am

Beam Splitter Problems

Post by John Howard »

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.
Din
Posts: 402
Joined: Thu Mar 12, 2015 4:47 pm

Re: Beam Splitter Problems

Post by Din »

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.
John Howard
Posts: 25
Joined: Fri Jul 06, 2018 11:36 am

Re: Beam Splitter Problems

Post by John Howard »

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.
holomaker
Posts: 772
Joined: Wed Jan 07, 2015 8:01 am

Re: Beam Splitter Problems

Post by holomaker »

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..
Loic74
Posts: 51
Joined: Sat Aug 10, 2019 9:09 pm
Location: France

Re: Beam Splitter Problems

Post by Loic74 »

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.
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