Re: ATM Re: CeO vs. Rouge

[Anthony Stillman <atmer@flash.net>]

All,

An article of some value regarding optical surface finish is "Production
and measurement of superpolished surfaces" by Johannes van Wingerden, Hans
Jan Frankena and Bertram A. van der Zwan and published in "Optical
Engineering" May 1992 Vol.31 No.5.  In this article the authors discuss
using grade H Cerirrouge, Fe2O3.  There polishing arrangement consisted of
a bowl feed(1) and stirrer with, in effect, MOT.  Their choice of
water/compound speed was such that the "centrifugal acceleration at the
edge of the pitch lap is about two times smaller than the gravitational
acceleration."  Onece the lap was well seated, the stirrer was removed and
the polishing continued while the compound settled.  Using this setup the
authors were able to obtain RMS roughnesses of from 0.1nm to 0.2nm(2) on
BK7.

In my ATMing experience I have usually used twice settled rouge with a new
lap made of 73, TOT, to finish surfaces I wish to be smooth.  I have not
had a problem with sleeking.  I have in each of these instances been
careful to work more slowly than usual and used distilled water to form the
suspension.  I have only used this method to finish a few mirrors, and
otherwise use CeO.


Anthony



1) A bowl feed consists of a deep bowl of water and compound around the
pitch lap with the level of water rising just above the level of the lap.
In some instances the bowl turns with the lap, in others only the lap
turns.  The stirrer is generally held static.

2) In the article the authors represent a conventionally polished surface
with an RMS roughness of from 0.47nm to 1nm.  Interferometric examination
of two ATM surfaces finished with CeO showed roughness a few times the top
of this range.