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

• I

## Main Question or Discussion Point

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.

Related Other Physics Topics News on Phys.org
Andy Resnick
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.
This type of problem is easily analyzed by using Jones vectors/matrices:

https://en.wikipedia.org/wiki/Jones_calculus

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

https://en.wikipedia.org/wiki/Jones_calculus
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.

Andy Resnick
We haven't gone through that.

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

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?
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.

Anyone?