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Re: [ATM] Fwd: [Fwd: [atm_free] Effect of pH on polishing fused silicawas 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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