[ATM] Phase contrast and the 10 incher.

[Scott Ewart]

    Keep in mind what the phase contrast test is for and just how 
sensitive it is.  According to Texereau, surface defects on the order 
of 1000th wave can be seen.  Larger-scale, broader shapes are not 
visible.  The Foucault test, on the other hand, does this quite well. 
That doesn't mean that the Foucault test can not see very small 
micro-ripple, just not as well or with as high contrast.
    I would not assume the worm tracks are large in amplitude at all, 
and this mirror may in fact perform well, with just a bit of scatter. 
That said however, if it were my mirror, I could not leave it alone 
and could not resist polishing it till it looked a bit better than 
that.

Scott Ewart


----- Original Message ----- 
From: "Arjan te Marvelde" <arjan.te.marvelde at hetnet.nl>
To: "Stephen Koehler" <s.c.koehler at gmail.com>
Cc: <atm at atmlist.net>
Sent: Wednesday, April 25, 2007 4:32 PM
Subject: Re: [ATM] Phase contrast and the 10 incher.


| Steve,
|
| 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'm close to giving up the guessing ... Dale you can reveal the 
answer now
| ;-).
|
|   Arjan
|
| ----- Original Message ----- 
| > So...this experiment is inconclusive.  I think that if the worm 
tracks
| > are on the surface to be picked up by interferometry, it would 
need
| > less noisy interferograms to see them.  I don't think this 
constitutes
| > proof that the worm tracks are below the surface.
|
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