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Value of the constant in 'variation of refractive index' 
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#1
Mar1713, 09:52 PM

P: 10

In optics, given the below formula
n_{λ}= A + B/λ^{2} + C/λ^{4} +...... 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 n_{λ} decreases. How do we measure the constant value of A,B and C at the first place? 


#2
Mar1813, 02:42 AM

Sci Advisor
P: 3,593

You measure the refractive index at several wavelengths and then you fit the formula to the values obtained.



#3
Mar2913, 04:30 AM

P: 10

Thank You DrDu.
While the above formula is for Optical Dispersion, then is it the same dispersion for the Abbe Number: V_{d}=(n_{D}1)/n_{F}n_{C} where n_{F}n_{C} is the dispersion according to this link http://glassproperties.com/abbe_number/ but somehow on other link I read that n_{F}n_{C} is called Principal Dispersion. I try to search on more about Principal Dispersion but there is almost none explanation about it. 


#4
Mar2913, 05:30 AM

Sci Advisor
P: 3,593

Value of the constant in 'variation of refractive index'
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. 


#5
Mar2913, 08:27 AM

P: 10

I understand about the line frequencies. Just that is it n(lambda)=n_F  n_C ?



#6
Mar2913, 09:27 AM

Sci Advisor
P: 3,593

I would try something like ## n(\lambda)=n_C+(n_Fn_C)\frac{1/\lambda_C^21/\lambda^2}{1/\lambda_C^21/\lambda_F^2} ##.



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