Intensity for circular polarised light through linear polariser

• dalind
In summary, the conversation discusses the effect of circularly polarized light passing through a linear polarizer, a quarter wave plate, and another linear polarizer. It is confirmed that the second polarizer decreases the intensity of the circular light in half and makes it linearly polarized. The role of the quarter wave plate is also clarified, with the understanding that it is only effective in the second flow described and would be useless in the first flow.
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

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

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

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?

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,

What is circular polarised light?

Circularly polarized light refers to an electromagnetic wave in which the electric field vector rotates in a circular motion as the wave propagates. This is in contrast to linearly polarized light, in which the electric field vector oscillates in a single plane.

What is a linear polariser?

A linear polariser is a device that selectively filters light waves based on their direction of polarization. It transmits light waves that are oscillating in a specific direction while blocking those oscillating in perpendicular directions.

How does a linear polariser affect circularly polarised light?

When circularly polarised light passes through a linear polariser, it is converted into linearly polarized light. The amount of conversion depends on the angle between the direction of polarization of the circularly polarized light and the transmission axis of the linear polariser.

What is intensity in relation to circular polarised light through linear polariser?

Intensity refers to the amount of light energy that passes through a given area over a specific period of time. In the context of circular polarised light through a linear polariser, intensity is affected by the angle of the polariser and the direction of polarization of the incident light.

How is intensity measured for circular polarised light through linear polariser?

Intensity can be measured using a light meter, which measures the amount of light energy that strikes a surface over a specific period of time. In the case of circular polarised light through a linear polariser, the intensity is measured after the light has passed through the polariser and is converted into linearly polarised light.

Replies
5
Views
2K
Replies
6
Views
1K
Replies
5
Views
1K
Replies
5
Views
3K
Replies
2
Views
816
Replies
4
Views
1K
Replies
5
Views
2K
Replies
2
Views
5K
Replies
4
Views
2K
Replies
2
Views
2K