# Relationship between the refractive index and absorption

1. Nov 14, 2013

### asdfghhjkl

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 :)

2. Nov 14, 2013

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. Nov 14, 2013

### asdfghhjkl

Ok, thank you.

4. Nov 14, 2013

Please give thanks by using the "thanks" button.

5. Nov 14, 2013

### DrDu

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. Nov 14, 2013

### Andy Resnick

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. Nov 15, 2013

### Claude Bile

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

Claude.