[ATM] refractive index of air

[Richard]

Hi Dominic-Luc,

Wednesday, August 8, 2007, 1:10:17 PM, you wrote:

DLW> OK, in any event, the Sellmeier equation looks new to me and that
DLW> is what I need to learn. I looked it up in Wikipedia, and that
DLW> equation looked pretty straightforward. Hopefully there is no typo
DLW> in the Wikipedia formula.

Wikipedia is normally fairly good, but there are many forms of the
Sellmeier equation. They are all basically just polynomials relating
N^2 to Lambda^2. In the case of that paper though, it is definitely N,
not N^2, as you can easily show by putting lambda=1 (micron) and
getting the correct answer of N=1.00027.

DLW> I am attempting to apply the Norman test (Burt A. Norman, S&T Nov
DLW> 1957, PP38-40) to plate glass for a Ritchey-Chrétien (RC) secondary.
DLW> In this test, light passes twice through the secondary; the back
DLW> surface is optically flat and silvered. For this test to work, it
DLW> is required that the eccentricity equals the ratio of refractive
DLW> indices of glass to air

Strange, I've not come across the Norman test before and that's twice
I've heard it mentioned in couple of days. I'm almost certain that the
parameters given for optical glass are with respect to air, not with
respect to vacuum, so you should have what you need without and
messing about. I'll read up on the Norman test and make sure I haven't
misunderstood.

DLW> that it should even be possible (practical???) to use plate
DLW> glass.

Possible. The amount of effort that goes into an RC secondary though,
I'd be inclined to go with the best material I could. Certainly be
better to aim for something lower expansion if possible.

DLW> I am polishing the primary; secondary has only seen rough grinding thus far.

Ah, you're doing it in the correct order :)

-- 

Best regards,
  Richard in the UK