Polarization and refractive index

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  • #1
Is there any relation between refractive index and polarization?
 

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  • #3
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Could you tell me what is a birefringent material?
 
  • #5
Have you tried the wikipedia article?
I did read the wikipedia article, but didn't understand why the materials refractive index depends on polarization.Please explain me. Thank you.
 
  • #6
sophiecentaur
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The speed of light in a medium is less than c because of the interaction of the light with the molecules. They become polarised (charge displacements) by the oscillating fields and this imposes a 'drag' on the wave going through. Mostly, more dense materials will slow the light down more (lead glass has a higher refractive index than cheap glass). Some crystals, because of the asymmetry of the charges and the atomic forces, will drag more for one polarisation of wave than another so this makes the speeds different. Iceland Spar (Calcite) has a very strong polarising effect. The Wiki article explains this; try it again.
 
  • #8
sophiecentaur
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Well, the Brewster angles are different in birefringent substances - because the refractive index depends upon polarisation.
 
  • #9
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Different in respect to what? I thought that the definition is the same as in isotropic media: the angle at which one polarization component is not reflected.
 
  • #10
sophiecentaur
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I only have a smart phone at the mo and find it difficult to read and write a lot. But I think the effect at the surface of a birefringence material is that the reflected ray will have elliptical polarisation due to the relative angles betwee the crystal lattice and the plane of the reflection.
Maybe someone could put us right on that one.
 
  • #11
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It may be, sure.
The Brewster angle will have a range of values, depending of the orientation of the normal to the optic axis of the crystal.
Maybe this is what you mean by "Brewster angles are different"? But for each orientation the reflection coefficient for one polarization become zero at the Brewster angle for that orientation. I think that this does not change.
 
  • #12
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1) Polarisation at an interface.
In general the transmission and reflection at the interface between materials with different refractive index is polarisation dependent. This is true even if both materials are isotropic or cubic.
http://en.wikipedia.org/wiki/Fresnel_equations
2) Birefringence.
In lower than cubic symmetry the propagation depends on the polarisation, so that a ray of arbitrary polarisation will be split into two rays with different propagation.
http://en.wikipedia.org/wiki/Birefringence
3) Not properly birefringence
The refractive index depends on the direction of propagation even in the cubic case. This effect becomes noticeable at frequencies approaching the excitonic resonance of the crystal. It is often lumped with true birefringence for lack of a specific term.
 
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  • #13
sophiecentaur
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It may be, sure.
The Brewster angle will have a range of values, depending of the orientation of the normal to the optic axis of the crystal.
Maybe this is what you mean by "Brewster angles are different"? But for each orientation the reflection coefficient for one polarization become zero at the Brewster angle for that orientation. I think that this does not change.
I am suggesting that there will not necessarily be an angle at which the horizontal vector is ever zero for a birefringent substance. This would be because there are two Brewster angles involved potentially (depending on the actual direction of arrival of the incident ray..
 
  • #15
sophiecentaur
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The Fresnel equations for isotropic-anisotropic, anisotropic-isotropic, etc. interfaces are given here:
Would it be possible for you to translate that article into a few words - just relating to the question? I tried to stagger through it but failed to pick up the important arm waving bit that I needed i.e. to say whether or not the brewster angle would be different for different arrival azimuths? I think that is implied but can't be sure.
 
  • #18
Andy Resnick
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Thanks for the other link, nasu. It's kind of bizarre: there's no discussion either in Born and Wolf or the Handbook of Optics (although there's a claim in vol. 4, 2.19 that the equations are present 'elsewhere in this Handbook'), even though there are detailed models of birefringent devices that use reflection: Nicol prisms, etc.
 
  • #19
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It may be. Depends what subscription deal your institution have.
Thanks for the other link, nasu. It's kind of bizarre: there's no discussion either in Born and Wolf or the Handbook of Optics (although there's a claim in vol. 4, 2.19 that the equations are present 'elsewhere in this Handbook'), even though there are detailed models of birefringent devices that use reflection: Nicol prisms, etc.
You are welcome.
There is a follow up too, I believe, by the same author.
 
  • #20
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It looks like you have to pay to see that.(?)
It may be. You tried through your library?
 
  • #21
sophiecentaur
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It may be. You tried through your library?
I don't have a college library. I can read books in my local Uni library but they do not let members of the public get on line resources. This situation is not uncommon for older PF members.
 
  • #22
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I don't have a college library. I can read books in my local Uni library but they do not let members of the public get on line resources. This situation is not uncommon for older PF members.
It seems that I cannot email you. Is this the case?
 
  • #23
sophiecentaur
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It seems that I cannot email you. Is this the case?
That''s right. I stopped doing PMs on forums some while ago. Sorry.
 

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