big silicon, was Re: re:RE: re:RE: Epoxy Granite, SPDT glass

Jon,
One can imagine such a big crystal though, at the present rate of silicon
increae, it will be, what, 100 years? till we see 2 m silicon used in
microlithography. Of course that will have to be fabbed in zero g.

Silicon can be cast into very nice optical elements. A place I used to work
had one fellow in a room full of glassware doing just that. He purified the
silicon and cast it into hemispherical shells about 6" diameter. There
wasn't any reason why they couldn't have been made larger. This is of
course polycrystalline silicon. It diamond turns very nicely.

Silicon is a fine material for lenses and mirror substrates; these require
similar properties to machine tool structures. The melting point is pretty
high, 1414 °C. It has low expansion, high thermal conductivity, high
stiffness/weight, low toxicity.

For the problem of making large optical elements in an interferometrically
controlled grinding and polishing machine, has anyone worked out how rigid
such a thing needs to be to prevent operational forces from distorting the
structure and reducing accuracy? Even if the cutting forces were taken out
of the structure separately from the metrology, rotation causes various
stresses, there are sure to be other problems.

The concept of a floppy machine making perfectly smooth cuts because the
scales are used to provide feedback to correct cutter location; that would
be fun to see. I think that's what Jack Hudler is proposing. Wish him
luck!


regards-
Elliot Burke

Message: 9
Date: Tue, 28 Feb 2006 20:34:06 -0600
From: Jon Elson <elson@...>
Subject: Re: re:RE: re:RE: Epoxy Granite, SPDT glass

Elliot Burke wrote:

>Jack,
>The PDF referenced below does not mention diamond turning glass. Lots for
>crystal materials can be diamond turned, maybe you could get a 2 m silicon
>blank?
>
>
>

I can guarantee with absolute certainty that nobody makes 2 M Silicon
crystals.
They are up to 12" or 300 mm, and that is already HUGE for a grown crystal!

Jon
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