Re: [ATM] Phase contrast and the 10 incher.

["Stephen Koehler" <s.c.koehler@gmail.com>]

Arjan and group,

> I have a couple of interferograms from Dale of this mirror that I will
> attempt to analyze, looking for any evidence of the high-frequency
> detail seen in the phase contrast pictures.

I tried analyzing one of the interferograms, but didn't have much
success finding evidence of worm tracks.  I put some images on the ATM
site:

     http://www.atmlist.net/contrib/s-dot-c-dot-koehler-at-gmail-dot-com/volna/

v101_igram.jpg shows the igram I analyzed.  This one has been reduced
to 400x400, but I analyzed it at 800x800 using the vortex transform
method.  The original interferograms are 1800x1800, but my analysis
program cannot handle interferograms this large.

v101_phase.png shows the wrapped phase from the analysis.  The red and
blue dots are residues (areas of poor phase resolution that can result
in phase unwrap errors).  This one has a lot of residues, but the
phase unwraps pretty well.

v101_wf.png shows the unwrapped phase after I have cancelled the
low-order Zernike terms (piston, tilt, defocus, coma, astig, and sa).
You can see some fringe print-through left over from the analysis.  I
need to remove artifacts like this, if I hope to find the worm tracks.

v101_fdom.png shows the Fourier domain of the phase, in which I will
do some filtering.  You can see an number of side lobe pairs, which
are left over from the analysis.  In particular, there is a secondary
pair of side lobes due to a fringe pattern overlying the main fringe
pattern in the interferogram, but at an angle.

v101_fdom_filt.png shows my attempt to filter out the artifacts I
don't care about.

v101_wf_filt.png shows the filtered wavefront.  It has a fairly smooth
appearance, because I filtered out a lot of low-frequency data.  If
worm tracks were present in this data, I would expect to see their
steep edges visible in this wavefront map.  There are some slight
streaks on the lower-right side of the map that could be worm tracks,
but they don't seem to correspond to anything on Dale's phase contrast
or Foucault images.  I see little evidence on the rest of the map of
any worm tracks.

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.

-- 
Steve Koehler
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