[ATM] Interferometer Fringe Contrast From Coated Mirrors

[mimas at charter.net (Donald "Don" Ware)]

As a result of a query I made to this list last month, I received two
suggestions for improving fringe contrast from coated mirrors.  While the
suggestion to use a layer of panty-hose stretched over a frame does indeed
work, I found that the fringes were broadened, probably due to some coherent
scattering from the threads in the hose.

Roger at the Mirror Lab in Arizona suggested using a pellicle filter.  These
are actually sold as pellicle beam splitters, transmitting a percentage of
the ray and reflecting the rest.  The one I was able to find transmits 67%,
which, because the ray passes through twice actually reduces the light from
the mirror by about 60%.

While a pellicle beam splitter that transmits 50% or even 40% would probably
be better, I am getting quite good fringe contrast from coated mirrors.
The fringes are only slightly broadened due to the extra optical elements in
the path.

Don Ware