Silicon Telescope Mirror

PFAFF2@delphi.com
Sat, 04 Mar 1995 20:23:25 -0500 (EST)

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> From: btk@ix.netcom.com (Bill Marriott)
> Subject: Silicon Telescope Mirror
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> >Silicon has a very low thermal expansion--about 2.5 ppm/K, which is
> about a third of most glasses. Combining this with good thermal
> conductivity and extremely good uniformity this should make a great
> telescope mirror.
> >--
> >Mark W. Lund, PhD
> >
> Interesting...
> Well, I have a 6" and a 8" (1.5" & 2" tk respectively) slabs, we'll see
> what happens...
> Thanks very much for the comments
>
> Further comments on polishing Silicon for those interested:
>
> Traditional polishing compound (cerium oxide) don't work with silicon
> With "chemo/mechanical" polishing, polishing silicon with a polyurathane
> pad is very easy, and it should be straight forward to produce a fairly
> good spherical surface, and with manipulating pad sizes, it may also be
> possible to 'zone' the sphere into a parabola.
>
> Polishing silicon with pitch is definitely an art. The alkaline slurries
> used with pad polishing tend to soften the pitch causing downgrading of
> the polished surface. There are techniques to get past this problem.
>
> Alpha Alumina (Al02), zirconium, and diamond (say a .05u finish) have
> all been used in pitch polishing of silicon, but they're all tricky...
>
> Obviously, anyone with experience in pitch polishing of silicon who has
> any comments please do pass on, this is one area of polishing expertise
> I am looking for improvement in.
>
> (This follows a line from sci.astro.amateur, but continued here for ATM
> intrests - hopefully not redundant
>
> Bill Marriott
> Forest Knolls, Ca.
> btk@ix.netcom.com
>
>
>
>
>
Stop by and talk to Jerry Logan at RTMC. That guy is a profession optician and has polished about every exotic material that is used in optics. Bob Pfaff