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Entry  Wed Feb 6 20:19:52 2013, Manasa, Update, Optics, G&H and LaserOptik mirrors 
    Reply  Thu Feb 7 14:10:25 2013, Manasa, Update, Optics, LaserOptik - AR Reflectivity - Bad data SN6_R.pngSN6_R.png
       Reply  Fri Feb 8 21:14:52 2013, Manasa, Update, Optics, G&H - AR Reflectivity  pr2.png27_1044419003.bmp
          Reply  Fri Feb 8 22:49:31 2013, Koji, Update, Optics, G&H - AR Reflectivity  
             Reply  Fri Feb 8 23:04:40 2013, Manasa, Update, Optics, G&H - AR Reflectivity  
          Reply  Sat Feb 9 19:34:34 2013, rana, Update, Optics, G&H - AR Reflectivity  
          Reply  Mon Feb 11 19:55:47 2013, Manasa, Update, Optics, G&H - AR Reflectivity  
             Reply  Wed Feb 13 09:28:56 2013, Steve, Update, Optics, G&H - HR plots 
Message ID: 8046     Entry time: Fri Feb 8 22:49:31 2013     In reply to: 8045     Reply to this: 8047
Author: Koji 
Type: Update 
Category: Optics 
Subject: G&H - AR Reflectivity  

How about to measure the AR reflectivity at larger (but small) angles the extrapolate the function to smaller angle,
or estimate an upper limit?

The spot separation is

D = 2 d Tan(\phi) Cos(\theta), where \phi = ArcSin(Sin(\theta) * n)

D = 2 d Tan(\phi) Cos(\theta), where \phi = ArcSin(Sin(\theta) / n)         (<== correction by Manasa's entry)

\theta is the angle of incidence. For a small \theta, D is propotional to \theta.

So If you double the incident angle, the beam separation will be doubled,
while the reflectivity is an even function of the incident angle (i.e. the lowest order is quadratic).

I am not sure until how much larger angle you can use the quadratic function rather than a quartic function.
But thinking about the difficulty you have, it might be worth to try.

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