Re: ATM What does a "super polished" surface look like?

[Anthony Stillman <atmer@flash.net>]

>..."super polish"
>...How do I get a smoother polish?
>...problems with the small laps causing...ripple
>...I still see some ripple in the ronchi.


Ed.

Superpolish is one of those terms that is a little slippery.  In the
literature RMS roughness under 1nm (10 A) are often so called.  At least
one shop I know of uses this term to describe surfaces which have residuals
(37 Zernikies removed) at and under 0.3nm (3 A) RMS.

A veneralble machine technique for obtaining super smooth surfaces is bowl
feed polishing.  Using a deep bowl to contain the slurry, with the tool
(lap) on the bottom, the mirror is polished normally.  The slurry rises
just to the level of the lap or slightly above.  The slurry may be gently
stired or it may not, relying instead on the rotation of the tool to do
some slight mixing.  The polishing compound tends to sink out of the
slurry.  There are other approaches but most techniques seem to bottom out
around 0.1nm.  A paper by Dietz and Bennett entitled "Bowl feed technique
for producing supersmooth optical surfaces" was published in Applied Optics
5 881-882 (1966).

Small tools raise zones.

Smoothing strokes remove correction.

A lot has been said and written on ways to make smooth surfaces.  Not all
of it is consistant.  For me refinining the polishing coumpound, managing
ph, using quality lap material (good pitch), working slowing with a lite
touch (no pin weight) and letting the substrate equilbrate all helps.
Using fused silica doesn't hurt either.

Anthony