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Re: [ATM] Fwd: [Fwd: [atm_free] Effect of pH on polishing fusedsilicawas Re. Session 24...]
Dale:
Great stuff, Dale; by any chance, have you taken interferometric results for
any of the mirrors that you pointed to? I'm curious as to whether the small
amplitude defects captured by phase-contrast will show up in interferometric
results (prior to analysis by Zernike fitting, of course, which could be
expected to smooth such defects out of existence). I would also expect that
an accurate interferometric analysis would need to account for the many
image artifacts introduced by coherent noise in the (typical) interferogram.
I think that several commercially available phase-shifting attachments do
this via a combination of polarization-control optics and phase shifting
either only the test beam or only the reference beam.
Scott Milligan
-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Dale Eason
Sent: Saturday, September 01, 2007 4:46 PM
To: atm@atmlist.net
Subject: Re: [ATM] Fwd: [Fwd: [atm_free] Effect of pH on polishing
fusedsilicawas Re. Session 24...]
Scott,
I have now imaged about 8 mirror in phase contrast.
While I don't know the absolute values I do have a good range of relative
surface roughness including three mirrors that show very little roughness in
phase contrast. I also have high resolution Foucault images of the many of
them.
Two of the smoothest are Carl Zambuto's and Mike Lockwoods's.
I have just imaged a mirror of unknown origin that may be the smoothest of
all. Too bad I know nothing else about it nor does the owner.
If there is interest I will provide a gallery in the Interferometry Wiki
where I already have examples.
http://starryridge.com/mediawiki-1.9.1/index.php?
title=Phase_Contrast
My current phase contrast setup has been simplified by the use of a super
bright LED in place of the projector. My slit is the same as I use for
Foucault imaging. The above site shows how to make a phase plate using a
candle. My camera is a Nikon Digital D40 and exposures of 20 seconds are
taken in a dark room.
Dale Eason
--- Scott Milligan <starzkey@charter.net> wrote:
> Interesting stuff here, guys; thanks for posting the link to the
> Applied Optics paper. Does anyone here have a low-cost way to monitor
> surface micro-roughness in a quasi-quantitative way? My own thoughts
> on this
> subject:
>
> 1. you have a friend that has access to an AFM or optical
> profilometer.
> 2. you implement some form of the Zernike phase-contrast method, and
> benchmark the patterns against some known reference standard.
> 3. you obtain a short-wave laser (wavelength < 450 nm), focus the
> output through a spatial filter to clean up the speckle, place the
> filtered output focal point approximately at the focal point of
> whatever mirror you are interested in, and in a dark room, observed
> the expanded,r eflected bean projected onto a white, matte background
> (white painted wall for instance).
> Rougher mirrors will show more distinct speckle pattern in the far
> field (try it, it really works if you can find all of the pieces).
>
>
>
> Scott Milligan
>
>
>
> -----Original Message-----
> From: atm-bounces@atmlist.net
> [mailto:atm-bounces@atmlist.net] On Behalf Of Guy Brandenburg
> Sent: Thursday, August 30, 2007 10:04 PM
> To: atm@atmlist.net
> Subject: [ATM] Fwd: [Fwd: [atm_free] Effect of pH on polishing fused
> silicawas Re. Session 24...]
>
> Interesting comments on pH levels and polishing with
> CeO2
>
> Alan Bromborsky <brombo@comcast.net> wrote: Date:
> Thu, 30 Aug 2007 17:37:14
> -0400
> From: Alan Bromborsky <brombo@comcast.net>
> To: Guy Brandenburg <gfbrandenburg@yahoo.com>
> Subject: [Fwd: [atm_free] Effect of pH on polishing fused silica was
> Re.
> Session 24...]
>
>
> To: atm_free@yahoogroups.com
> From: "Mark Cowan" <toolontop@yahoo.com>
> Date: Thu, 30 Aug 2007 19:47:54 -0000
> Subject: [atm_free] Effect of pH on polishing fused silica was Re.
> Session 24...
>
> I was looking through the paper I cited
> in the last post and noted the following about hydration layers and
> silicate
> redeposition:
>
> Buffering the CeO2 slurry to pH 4 increased the drag greatly, but
> according to the paper and the assorted micrographic and AFM imagery
> the resulting surface is much smoother - /because/ (they
> say) the redeposition
> from the slurry is greatly reduced. Thus the polishing action is
> surface removal primarily. They also say the lap lasts much longer
> because the "ceria particles are suspended in the slurry rather than
> embedded in the lap." The lack of the redeposited layer means that
> the final surface is made from the pure substrate, and so might bond
> to the coating better, improving coating life.
>
> Perhaps you need to start with a fresh lap for this experiment. I
> plan to test some of this with the robotic figuring machine, which is
> much more capable than I am of maintaining constant lap speed against
> high resistance.
>
> Best,
> Mark
>
> > Here's an interesting experiment that demonstrates that.
> >
> > H. Highstone set me a copy of an Applied Optics paper from '92 (pp
> > 7164-7172, Vol 31, no 34) that explored the use of various agents >
> (CeO2, ZrO2, Al2O3, Y2O3, YF3) on fused silica at varying pH ratios.
> > Al2O3 has by far the highest roughness of any of these compounds.
> > Anyway, lowering the pH from 7 to 4 with CeO2 on fused silica
> lowers > the roughness by a factor of almost 4x under controlled
> conditions.
> > You can use citric acid to buffer the pH of a slurry down to these
> > levels. I've tried it. The lap drag immediately becomes
> /enormous/, > to the point that the lap can't be moved smoothly.
> Although it may > result
> in lower roughness under machine control, by hand the result > was
> horrible, with roughness quite visible under Foucault testing.
>
>
>
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