Value of the constant in 'variation of refractive index'

  1. In optics, given the below formula

    nλ= A + B/λ2 + C/λ4 +......

    where A, B and C are constants.

    From the above relationship we can deduce that as the wavelength λ increases, the variation of refractive index nλ decreases.

    How do we measure the constant value of A,B and C at the first place?
  2. jcsd
  3. DrDu

    DrDu 4,638
    Science Advisor

    You measure the refractive index at several wavelengths and then you fit the formula to the values obtained.
  4. Thank You DrDu.
    While the above formula is for Optical Dispersion, then is it the same dispersion for the Abbe Number:


    where nF-nC is the dispersion according to this link

    but somehow on other link I read that nF-nC is called Principal Dispersion. I try to search on more about Principal Dispersion but there is almost none explanation about it.
  5. DrDu

    DrDu 4,638
    Science Advisor

    n_F is the index of refraction for blue light while n_C is for red light (see the table with the line frequencies).
    One assumes that for glass the dispersion is approximately linear over the optical frequency range.
  6. I understand about the line frequencies. Just that is it n(lambda)=n_F - n_C ?
  7. DrDu

    DrDu 4,638
    Science Advisor

    I would try something like ## n(\lambda)=n_C+(n_F-n_C)\frac{1/\lambda_C^2-1/\lambda^2}{1/\lambda_C^2-1/\lambda_F^2} ##.
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