Interferometry in Green

Well, it turns out that one of the problems I was having with my green laser and the VRP-M film is my shutter.

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When it opened it set the table to ringing for at least a full second.  My 2-4 second exposures were incredibly dim because they were getting fogged for the first second.  I found this out after setting up an interferometer (shown above, click for a larger picture) opening and closing the shutter while it was going.  The fringes really moved when the shutter closed but as no light would have been reaching the film, I didn’t care about that.  Have it shake the table when opening was a problem though.

I tried all sorts of things to improve the isolation of the shutter and damp the vibrations it was putting out but in the end I had to give up and make a shutter from scratch.

I took a panel meter and attached a multi-layered piece of aluminum foil and used that reflect the incoming beam and create a beam dump on the inner surface of the meter housing.  Painting the whole thing black created a nice little box to keep the beam in.

After putting a couple of beads of silicone where the meter arm rests against the coil I ended up with a nice quiet shutter that didn’t disturb the fringes at all.

It’s being put through its first hologram-making test right now.

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Michael Harrison

Husband, Programmer, Irish dancer, tinkerer, astronomer, layabout (as much as possible)

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