Re: Twyman Green Interferometer

From: Helpful person (rrllff_at_yahoo.com)
Date: 06/28/04 

Date: 28 Jun 2004 11:31:50 -0700

Michael Koch <astroelectronic@gmx.net> wrote in message news:<40DEF089.81643FA3@gmx.net>...
> Hi,
>
> > My question is, why do most (if not all) Twyman Green (and Michelson)
> > interferometers use a 45 degree beam splitter?
>
> The surface accuracy of the beamsplitter can be worse by a
> factor of sqrt(2) if the angle is 45 degrees (compared with
> 0 degrees).
> It doesn't make a big difference if you buy a 50x50mm 1/10
> wave or a 71x50mm 1/7 wave beamsplitter.
>
> Michael

Thanks. That is true. That gives an excellent arguement for staying
with the 45 degree angle. However, in my case I already have an
excellent 3 inch diameter beam splitter and can increase the aperture
of the instrument by reducing the angle of incidence at the beam
splitter. I would like to have a 2 inch aperture.

Does anyone know of any other reason for staying with a 45 degree
angle for the beam splitter?

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