Re: ATM zero expansion glas

[Anthony Stillman <atmer@flash.net>]

>...One such obstacles is thermal behaviour


Vladimir,

Personally I think that the majority or ATM optics projects can do with out
ultra-low expansion materials.  I'm not saying that they aren't nice.  I
would choose a free piece of Pyrex over soda-lime.  And free fused silica
over either.  But only because I could sell the later for more and get a
bigger piece of Pyrex.   From my perspective the real reason for choosing
low-expansion materials is the time it takes to manufacture the optic.
Fused silica doesn't need to soak (equilibrate) as long before it can be
tested.  This lowers the manufacturing cost.  We ATMs generally have more
time than money, so it's an easy chose.

As for ceramics like Zerodur and sitall, well, not all are the same.  They
are made to have a low expansion zone around a specified working
temperature.  Outside this region their low expansion performance is
degraded.  Be careful buying surplus material, specifications are important.

Fused silica and the low expansion ceramics are hard and tough. They make
powder of silicon-carbide in mere moments.  Generating is a big plus.  It
has been reported that the ceramics can be difficult to polish.  My
experience is that they just take longer.

In my opinion, the most valuable tools a novice or experienced ATM can
possess are persistence the ability to say, it's good enough.


Anthony