Relationship between the refractive index and absorption

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Discussion Overview

The discussion revolves around the relationship between the refractive index of materials and their light absorption characteristics, particularly in the context of geological thin sections. Participants explore whether a higher refractive index correlates with higher absorption and how intensity of light relates to refractive index.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions if there is a relationship between refractive index and light absorption, suggesting that a higher refractive index might indicate higher absorption.
  • Another participant asserts that there is no direct relation between light intensity and refractive index, noting that refractive index is dependent on the speed of light in the medium and varies with wavelength.
  • A participant introduces the Kramers-Kronig relation, indicating that there is a connection between absorption and refractive index, but emphasizes the need for knowledge of these properties across all frequencies to deduce one from the other.
  • Another participant mentions that absorption can be modeled with a complex refractive index, where the real part represents the refractive component and the imaginary part represents absorption, and notes their interdependence through the Kramers-Kronig relation.
  • A later reply discusses intensity-dependent components of the refractive index, specifically mentioning Kerr nonlinearity and saturable absorption.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between refractive index and absorption, with some suggesting a connection and others denying a direct relationship with light intensity. The discussion remains unresolved with multiple competing perspectives present.

Contextual Notes

Participants highlight that the relationship may depend on specific conditions, such as the frequency of light and the medium's properties, indicating that assumptions about these factors are important but not fully explored.

asdfghhjkl
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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 :)
 
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asdfghhjkl said:
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 :)
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:
Ok, thank you.
 
asdfghhjkl said:
Ok, thank you.
Please give thanks by using the "thanks" button. :biggrin:
 
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.
 
asdfghhjkl said:
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?

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

Claude.
 

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