# Relationship between the refractive index and absorption

1. ### asdfghhjkl

15
Hello,

I was wondering is there a relation between the refractive index of the material and the amount of light the material absorbs (e.g. the higher n means higher absorption)? If so what is then a relation between the intensity of the light and the refractive index?

p.s. I am trying to apply this to some geological thin section observations, thus a simple explanation would be appreciated.

Thank you :)

1,539
There is no relation between the intensity of light and the refractive index.Refractive index depends on the speed of light through the medium.It varies with wavelength too.

Last edited: Nov 14, 2013
3. ### asdfghhjkl

15
Ok, thank you.

1,539
Please give thanks by using the "thanks" button.

5. ### DrDu

4,512
There is a relation between absorption and refractive index which is known as Kramers Kronig relation:
http://www.rp-photonics.com/kramers_kronig_relations.html
However, to deduce the one from the other, you need to know the absorption or refractive index ideally for all frequencies.

6. ### Andy Resnick

6,087
Echoing DrDu, absorption is often modeled by allowing the refractive index to be complex-valued (say n = η + iκ) the real part η is the 'refractive' component and the imaginary part κ the 'absorption' component. The components are not independent but related through the Kramers-Kronig relation.

7. ### Claude Bile

1,479
The intensity-dependent component of the refractive index is known as the Kerr nonlinearity (real part) and saturable absorption (imaginary part).

Claude.