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n (Sellmeier equation)

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n (Sellmeier equation) diagram
calc
The Sellmeier equation uses the Kramers-Kronig relationship between optical absorption and refractive index to calculate the wavelength-dependant refractive index based on constants relating to key absorbances.
B1
C1
B2
C2
B3
C3
Wavelength

Refractive index
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notes
Fill in the Sellmeier coefficients for a given substance in the blue boxes, along with a wavelength of interest, and the refractive index will be given in the orange box.
The sellmeier "B" coefficients are the oscillator strengths of transitions, and the "C" coefficients are the squares of the respective transition energies (as photon wavelengths). Thus, knowing the experimental or calculated absorption spectrum of a substance, it is possible to predict the refractive index.