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Polarization and refractive index

  1. Mar 12, 2015 #1
    Is there any relation between refractive index and polarization?
     
  2. jcsd
  3. Mar 12, 2015 #2

    Andy Resnick

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    If the medium is birefringent, yes.
     
  4. Mar 12, 2015 #3
    Could you tell me what is a birefringent material?
     
  5. Mar 12, 2015 #4
    Have you tried the wikipedia article?
    "Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light."
     
  6. Mar 12, 2015 #5
    I did read the wikipedia article, but didn't understand why the materials refractive index depends on polarization.Please explain me. Thank you.
     
  7. Mar 13, 2015 #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. Mar 13, 2015 #7

    NascentOxygen

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  9. Mar 13, 2015 #8

    sophiecentaur

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    Well, the Brewster angles are different in birefringent substances - because the refractive index depends upon polarisation.
     
  10. Mar 13, 2015 #9
    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.
     
  11. Mar 13, 2015 #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.
     
  12. Mar 13, 2015 #11
    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.
     
  13. Mar 13, 2015 #12
    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.
     
    Last edited: Mar 13, 2015
  14. Mar 14, 2015 #13

    sophiecentaur

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    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. Mar 15, 2015 #14

    Andy Resnick

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  16. Mar 15, 2015 #15

    sophiecentaur

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    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.
     
  17. Mar 15, 2015 #16
  18. Mar 16, 2015 #17

    sophiecentaur

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  19. Mar 17, 2015 #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.
     
  20. Mar 17, 2015 #19
    It may be. Depends what subscription deal your institution have.
    You are welcome.
    There is a follow up too, I believe, by the same author.
     
  21. Mar 17, 2015 #20
    It may be. You tried through your library?
     
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