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Does light have 2 electric field components?

  1. Oct 10, 2014 #1
    Hi, we are currently working on Huygens constructions and i'm having trouble visualising it. I understand that, say if a light wave is incident upon an anisotropic material that if you consider it's electric field going perperdicular in one direction it will be refracted differently than if you consider it's electric field perpendicular in another direction (due to the refractive index of the material effecting each perpendicular componant differently.)

    My question is does light have 2 perpendicular componants of electric field? so you would effectively have 2 beams going through the material at different speeds, due to one perpendicular componant of light being refracted more than the other? Or would you consider each perpendicular componant seperately (i.e. it only has one at any time)?

    Getting a bit lost with this!

    Please see attached images, the dotted line is for one componant, the plane wave line is for the other perpendicular componant.

    How do I visualise this?

    Thanks for any help!
     

    Attached Files:

  2. jcsd
  3. Oct 10, 2014 #2

    jtbell

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    Staff: Mentor

    Yes. You can use this to separate a single beam into two perpendicularly-polarized beams. See the images here:

    http://en.wikipedia.org/wiki/Birefringence
     
  4. Oct 10, 2014 #3

    Thanks for the answer, but how would you visualise this? So the standard image (show below) is not correct?

    light_magnetic.jpg

    Maybe i'm confusing things, i'm trying to visualise a beam of light that has two perpendicular electric field componants, and i cant. I looked at the images on the wiki page, but where's the magnetic field?
     
  5. Oct 10, 2014 #4
    Any vector can be decomposed into two perpendicular components. Like when you decompose the weight of a body into normal and tangential components on an inclined plane. It does not mean that the body has two weights, does it?
    In the image the electric field is horizontal. You could decompose it into two components at 45 degree angles from horizontal (above and below horizontal plane). It's not an unique decomposition, for sure. Just an example. Then you can imagine two waves with propagating simultaneously, with the two electric field and the appropriate magnetic fields (B perpendicular to E in air or vacuum)
    As long as the wave is in an isotropic medium, the two components have the same phase and you can (imaginary) put them together to obtain a wave with a single E component. In an anisotropic medium the two components will propagate with different speeds and a phase difference will appear.

    Remember that this is just a model to help operate with waves in anisotropic medium. The wave is not actually "separated". The original plane or spherical wave is distorted due to the anisotropy of the medium and the propagation becomes more complicated. An easy way to describe what happens is to use this component model. Same as decomposing vectors or motion to do calculations does not mean that we actually have two "objects".
     
  6. Oct 10, 2014 #5

    Thanks, some very good analogies there! you really helped clear things up in my head! thankyou very much!
     
  7. Oct 10, 2014 #6
    You are very welcome.
     
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