[ATM] new metal ion sputter method announced

[David Weinshenker]

Jan Bentz wrote:
> Perhaps a better bet for optics is erosion rather than deposition.  Its 
> done with an ion gun in a vacuum chamber and knocks the atoms off the 
> surface of the glass.  The gun's motion is driven by stepper motors in  
> 2 dimensions and controlled by computer program to move in a 
> predetermined spiral pattern until the desired figure is reached.  
> Alternately the gun is driven across the rotating glasses diameter at 
> certain rate.  The advantages were cost, no edge problems, ability to 
> monitor figure interferometrically and less surface roughness.  I know 
> that several large companies were doing this  including Kodak and IBM  
> in the late '70's and early '80's.  I don't know what the status of the 
> process is now.

This sounds like it may well be the "ion milling" or "ion figuring"
process that I've seen references to. I believe it's been used for
a number of telescope mirrors, including the multiple segments of the
two Keck telescopes in Hawaii...

-dave w