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I Tilted Polarizer

  1. Oct 31, 2017 #1
    https://www.dropbox.com/s/t5lv4nlunn35ok8/phy1.PNG?dl=0
    https://www.dropbox.com/s/ktc9pj7qmqhejrv/phy2.PNG?dl=0
    https://www.dropbox.com/s/qbjz1p1gokvsgj2/Capture3.PNG?dl=0

    I googled "polarizer film diagram" and "malu's law" and "polarizer physics" to obtain the pictures in this thread.
    I understand we usually study polarised light phenomena by rotating polaroids.

    I am curious about this : What would happen, or what would be the outcome/result if the first or second Polaroid in a setup shown in the above two images, is *tilted* forward or backwards? as in, the Polaroid is firm on it's base, just that it is *tilted* either forward or backwards. What would be the outcome when polarised light, and unpolarised light pass through the Polaroid?
    Will light still pass through, or be polarised, through tilted Polaroid(s)?
    Or is it just that Intensity will be affected, or Polarised light will not emerge straight, and rather at an angle?
    Will light still be polarised the same way and angle as a untilted Polaroid(such as the base perpendicular to the table, untilted), just that less light is passed through?

    Sorry I do not have a lab or the required gear to experiment this myself.


    Secondary question :
    How does the cross section of a Polariser looks like; how does a Polariser polarise light?
    Isn't light polarised by passing through tiny vertical slits? Why is light not polarised through the tiny slits of a diffraction grating?
    Is a Polariser made up of many sheets of polaroids?

    A very large and warm Thank-you to all that have replied
     
    Last edited: Oct 31, 2017
  2. jcsd
  3. Oct 31, 2017 #2

    Andy Resnick

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    The answer to your first question is complicated, the specifics depend entirely on the surface (which is why normal incidence is used in class). For what it's worth, here's a comprehensive report on the subject:

    https://repository.tudelft.nl/islan...92-4960-b0fe-5ccbc95da562?collection=research

    (you want chapter 3).

    As for the second question, that isn't a good analogy. If anything, the polarization component *perpendicular* to the slits passes through, while the polarization component parallel is blocked. To be sure, far-infrared polarizers are indeed parallel wires. However, polarizers can be constructed from a variety of materials, not just sheets of Polaroid: certain prism geometries separate orthogonal polarizations.
     
  4. Oct 31, 2017 #3

    sophiecentaur

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    If a polariser consisted of narrow slits then a 'perfect' polariser would need to have infinitely thin slits - which would admit no light. In fact, the energy from an unpolarised source through a perfect polariser only drops by half.
     
  5. Oct 31, 2017 #4

    Andy Resnick

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    In the case of FIR polarizers, the wire width and spacing are subwavelength- not a big deal when the wavelength is 100 um.
     
  6. Oct 31, 2017 #5

    sophiecentaur

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    I am a tad confused here. A good microwave polariser can be made in a similar way with a grid of parallel wires (spaced by perhaps a tenth of a wavelength, IIRC). In that case, currents that are induced in the wires that will reflect the wave components that are parallel with the wires and the spaces in between the wires have no induced currents so the wave component passes through. So the transmitted polarisation is normal to the direction of the slots. Is the action of a FIR polariser different from that?
     
  7. Nov 1, 2017 #6

    Andy Resnick

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    nope- exactly the same. Did I say otherwise?
     
  8. Nov 1, 2017 #7

    sophiecentaur

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    No you didn't say otherwise. It's just that the 'slots' are not in the same orientation as the resulting polarisation. That could be regarded as counter-intuitive and certainly doesn't tie in with the over simplified explanations that we see in textbooks. Also, I thought polaroids worked on absorption of the other polarisation and that is not how an RF polariser works.
    It is all more complicated that at first sight and what pictures of waves on ropes and slots in metal sheets would imply.
     
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