[ATM] Phase contrast and the 10 incher.

[Stephen Koehler]

Arjan,

> Based on the clarity of the wormtracks all over the mirror in the foucault
> image, I would say they have to be multiple wave faults, if they were
> surface features. Such deviations would surely show up in the raw
> interferogram, but all I can see is low frequency abberation, and only to
> the right edge there's a hint of phase shift.

I disagree.  The overall  "donut" from testing at COC is about one
wave of error.  These worm tracks are much more subtle.  I ran a quick
simulation where I took a perfect wavefront, and lowered a rectangle
of the surface (about the size of one of the worm tracks) by 1/100
wave.  It was easily visible in a simulated Foucault image, and at
about the same intensity as in Dale's Foucault image.  This size of
defect would not be visible as perceptible bending in the
interferogram fringes.

-- 
Steve Koehler