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What happens to polarised light?

  1. Jul 24, 2010 #1
    I wasn't sure which forum this came under, so...

    I've read the basic idea of polarised lenses: light rays have an 'orientation', and when a light beam passes through a polariser only certain orientations get through.

    1. But what happens to the rest of the light i.e. those rays that don't get through? Are they absorbed? Re-emitted in a different direction? Why?

    Any help would be great,
     
  2. jcsd
  3. Jul 25, 2010 #2
    Depends on the particular mechanism of polarisation.
    In the case of 'Polaroid' or LCDs the off-plane light is absorbed.
    In the case of Brewster angle polarisation (water, glass) it's simply reflected.

    I don't know of any cases where it's actually rotated - it might be possible.
     
  4. Jul 25, 2010 #3
    Lots here:
    http://en.wikipedia.org/wiki/Polarizer

    in brief:

    "...Polaroid film was in its original form an arrangement of many microscopic herapathite crystals. Its later H-sheet form is rather similar to the wire-grid polarizer. It is made from polyvinyl alcohol (PVA) plastic with an iodine doping. Stretching of the sheet during manufacture ensures that the PVA chains are aligned in one particular direction. Electrons from the iodine dopant are able to travel along the chains, ensuring that light polarized parallel to the chains is absorbed by the sheet; light polarized perpendicularly to the chains is transmitted. The durability and practicality of Polaroid makes it the most common type of polarizer in use, for example for sunglasses, photographic filters, and liquid crystal displays. It is also much cheaper than other types of polarizer.

    An important[citation needed] modern type of absorptive polarizer is made of elongated silver nanoparticles embedded in thin (≤0.5 mm) glass plates. These polarizers are more durable, and can polarize light much better than Polaroid film, achieving polarization ratios as high as 100,000:1 and absorption of correctly-polarized light as low as 1.5%.[2] Such glass polarizers perform best for short-wavelength infrared light, and are widely used in optical fiber communications."
     
  5. Jul 25, 2010 #4
    Okay thanks - that's useful!

    So some of the light is absorbed by the electrons in the polariser, which move back and forth along the molecule chains (which are all parallel to each other).

    For clarity though - why do the electons only absorb the light which has its electric field perpendicular to the direction of the molecule chains? Is it something to do with the direction of an electric force?
     
  6. Jul 26, 2010 #5
    I remember my optics professor saying that polarizers were conducting in one orientation and non-conducting in another. Thus the voltage along one axis of the light is zero because of the conductor (IE. the light gets "absorbed" if it's polarized in the particular orientation where the electric field is along the conductor).
     
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