Re: ATM Interferometer

[astillma@nit.AirTouch.COM (Anthony Stillman)]

Regarding Interferometric surface measurement

I would like to point out that most optical tests that ATMs utilise, measure
slope, or slope error since we compare what we see to what we expect.  Most 
interferometric tests measure profile.  While its true that profile is usually 
how we discuss glass quality, 1/10 wave rms and what not, slope or rather 
slope error is what mostly impacts optical performance.  The typical
interferimetric measurement is not that good at discerning slope error.  It 
can be done, but it isn't nearly as easy as the more traditional ATM tests.  
I do not mean to imply that interferometers don't have uses, just note 
that they are not a silver bullet, and are prone to measurement interpretation
errors.

Anthony