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I Intensity as light passes through two quarter-wave plates?

  1. Apr 17, 2018 #1
    I have unpolarized light passing through a polarizator assuming the angle 0°. The polarized light then passes through two quarter-wave plates, the first one with the angle of 45° (maximum intensity) and the other one. Then it passes through a last polarizator having an orientation perpendicular to the first polarizator, that is 90°.

    What is the intensity output? I don't know how the polarized light behaves when reaching the quarter-wave plates. What angle should the second one be for maximum transmission?

    It is in my understanding that quarter-wave plates only causes a phase shift in the electric components, 45° will cause circular polarization and anything else elliptically. Reaching the other should make it linearly polarized. I just don't understand how to calculate the output intensity. I have read that quarter-wave plates does not affect intensity but how come they can cancel each other out then.
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  3. Apr 17, 2018 #2

    Andy Resnick

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    This type of problem is easily analyzed by using Jones vectors/matrices:

  4. Apr 18, 2018 #3
    We haven't gone through that.

    Is there another way of determining the intensity as it passes through:

    Polaroid (0°) → Quarter wave-plate (45°) → Quarter-wave plate (?°) → Polaroid (90°)

    The second quarter-wave plate should have an angle in which intensity transmitted total intensity is at maximum. Not sure how to get it.
  5. Apr 18, 2018 #4

    Andy Resnick

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    I'm sure there are other ways, using the Jones calculus is just the easiest. Do you understand what is meant by 'Quarter wave-plate (45°)': what is at 45°? Try thinking about this- what is the polarization state of the light after it passes through the first retarder?
  6. Apr 19, 2018 #5
    Through the first polaroid it become linearly polarized. I'm not sure what the angle of the quarter-wave plate does. I know that it phase shifts the electric vector components so they oscillate with a 90 degree difference, basically circular polarization. Not sure what 45 degrees does on it.
  7. Apr 21, 2018 #6
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