ATM thermal expansion coefficient of plate glass

[3D@taconic.net]

Thank you for helping me get the parameter on  the flatness of plate 
glass. (3-8 waves/inch). I ran the calculation and determined that it 
would produce less than 1 Angstrom spectral error in a diffraction 
grating. Calculation is posted at

http://www.drillamerica.com/PDF/plate_calc.pdf

The performance is confirmed in the field.  Optometrics, a major 
manufacturer of precision gratings, uses plate glass as substrate.

Now I need to know its thermal expansion coefficient, since this 
would cause a phase shift in any grating grooves directly built on the 
surface of the glass. I know that plate glass is eschewed for mirror 
blanks for this reason, at least compared to superior glasses such 
as Pyrex and Zeodur, but it might work in my special application.

Tom Ditto
"Listen to the colors of the universe."