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Homework Help: Finding refractive index by interpolation

  1. Dec 20, 2006 #1
    The problem is described here:
    http://phstudy.technion.ac.il/~wn117066/Problems2.pdf [Broken]

    In question 1 I need to find the refractive indices for both polarizations at 760nm. I'm not quite sure how to go about this - which model of dispersion best fits Calomel?

    (I'm done with the exercise itself, now I just need to plug in the refractive indices values to get a numerical result...)

    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Dec 20, 2006 #2


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    Interpolation is the process of estimating a value from a discrete set of ordered pairs of data. You could use a linear interpolation, or since you have three rather widely spaced points you could use a second degree polynomial (parabola) to fit the data and extract the interpolated data point. Most graphing calculators have a built in fitting program for this, probably called a quadratic regression. Or you could derive the equation from the three data points you are given and use it to find the additional popint you need.

  4. Dec 20, 2006 #3
  5. Dec 20, 2006 #4
    I'm well familiar with the definition of interpolation, thank you.

    I considered that route, but having only 3 data points available makes it a bit hard to find those coefficients...
  6. Dec 20, 2006 #5
    You could also use other models with fewer coefficients -- since yeah, you only have three points and probably don't want to trucate the Sellmeier series approach by too much (sorry I didn't notice that :uhh:):

    http://www.optics.arizona.edu/Palmer/cgi-bin/index/dispeqns.pdf [Broken]

    The Cauchy model is common.
    Last edited by a moderator: May 2, 2017
  7. Dec 20, 2006 #6
    Thanks, that seems sensible. I'll report back if anything goes awry...
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