Intensity for circular polarised light through linear polariser

[dalind]

Hi,

does the intensity change when circularly polarised light passes through a linear polariser?
I am thinking of a flow like this: natural light -> vertical linear polariser -> quarter wave plate -> horizontal linear polariser -> intensity?

After the first polariser, the intensity is 50%, the quarter wave plate changes the linear polarisation to circular. But does the horizontal linear polariser decrease the intensity again?

Edit: Another flow would be natural light -> 45° linear polariser -> quarter wave plate -> - 45° linear polariser -> intensity? Since I think the polarisation is not affected by the quarter wave plate if the light is polarised vertically, I think the first flow would result in a complete absorption of the light by the second polariser (Intensity 0), right?

Thank you.

Cheers,
dalind

 

[dauto]

Yes, the second polariser cuts the intensity of the circular light in half.

 

[Meir Achuz]

... and makes it linearly polarized.
A plane polarizer treats circularly polarized light the same as it treats unpolarized light.

 

[dalind]

Okay, thanks. That's what I thought. And this only works for the second flow I described, for the first one the quarter-wave plate would not change the polarization and would therefore practically be useless, right?

 

[sardar]

cy

Hello dalindcy,

Thank you for your question. The answer to your question depends on a few factors, such as the angle of incidence of the light on the linear polariser and the orientation of the linear polariser and quarter wave plate.

In general, when circularly polarised light passes through a linear polariser, the intensity will be reduced. This is because the linear polariser only allows light with a specific polarization direction to pass through, while the circularly polarised light has components with both horizontal and vertical polarization directions.

In your first flow, if the quarter wave plate is oriented in a way that converts the circularly polarised light to linearly polarised light with a horizontal orientation, then the horizontal linear polariser will decrease the intensity again. However, if the quarter wave plate is oriented in a way that converts the circularly polarised light to linearly polarised light with a vertical orientation, then the horizontal linear polariser will not affect the intensity.

In your second flow, if the 45° linear polariser is oriented in a way that allows both horizontal and vertical polarised light to pass through, then the quarter wave plate will not have any effect on the intensity. However, if the 45° linear polariser is oriented in a way that only allows horizontal or vertical polarised light to pass through, then the quarter wave plate will have an effect on the intensity.

In summary, the intensity of circularly polarised light passing through a linear polariser will depend on the orientation of the linear polariser and the quarter wave plate. I hope this helps to clarify your question. If you have any further questions, please don't hesitate to ask.

Best,