1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

  1. Apr 17, 2018 at 5:37 AM #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.
     
  2. jcsd
  3. Apr 17, 2018 at 2:17 PM #2

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

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

    https://en.wikipedia.org/wiki/Jones_calculus
     
  4. Apr 18, 2018 at 5:50 AM #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 at 7:04 AM #4

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

    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 at 5:18 AM #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 at 6:49 AM #6
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Loading...