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I Recovering polarized light

  1. Apr 26, 2016 #1
    I was curious; having gone through a class covering Waves, in various forms encountered, we covered evanescent waves. These waves seen to be able to penetrate through some mediums, even able to be recovered. An example might be sound passing through water, then air, and then back into water.

    My question is, can one recover polarized light along this line of reasoning, that is, restoring the light to its unpolarized condition?
  2. jcsd
  3. Apr 26, 2016 #2
    In most cases (camera filters, sunglasses) light is polarized by filtering out the light of the other polarization and passing only the desired polarization.

    So, if you have unpolarized light coming into the filter, you have (at most) 50% polarized light being transmitted. The rest is reflected or (usually) absorbed.

    You may be able to turn the polarized light that was transmitted back into unpolarized light, but the 50% (or more) that was reflected or absorbed is gone for all practical purposes.

    I suppose if it is reflected, you can try and set up an optical system of mirrors to catch it and recombine it again.
  4. Apr 26, 2016 #3
    Sound going from water to air does not suffer total internal reflection so no evanescent waves.
    The speed of sound in water is higher than in the air, not the other way (as it is for light).

    I don't understand your link between evanescent waves and "recovering polarization".

    An example of "recovering" the evanescent waves may be the technique called TIRF (Total Internal Reflection Fluorescence) where the evanescent waves are used to excite fluorescence of some beads or cells with dyes situated close enough to the interface.
  5. Apr 26, 2016 #4

    Andy Resnick

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    Evanescent waves are not polarized in the usual sense- they are nonpropogating waves. They can be 'recovered' (frustrated total internal reflection is one example, total internal reflection fluorescence microscopy is another).

    But you do ask an interesting question- given polarized light undergoing frustrated total internal reflection, what is the polarization state of the light that 'tunneled' through? It seems to be identical to the original polarization, but I need to read the article more closely:

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