Classical optics: Lambda-quarter plates

[Niles]

Hi

Say I have a magnetic field point in some well-known direction, and I have linearly polarized light incident in that direction. I want to convert my π-polarization to σ-polarization, so I find my lambda-quarter plate.

However, how do I know whether it produce σ+ or σ-? Do they come with a manual, or do people calibrate them by themselves? I'm not sure how I would do this.


Niles.

 

[Andy Resnick]

I'm confused by your question- first, the magnetic field will not point along the polarization direction, the polarization is defined by the electric field. Second, to rotate linearly polarized light (if π- and σ- refer to p- and s-polarized) you would use a 1/2 wave plate, not a 1/4-wave plate.

 

[mfb]

lambda/4 wave plates should have some indication where the fast and the slow axes are. The orientation relative to the (linear) polarization of incoming light will determine how the polarization afterwards looks like.

 

[Niles]

I'm confused by your question- first, the magnetic field will not point along the polarization direction, the polarization is defined by the electric field. Second, to rotate linearly polarized light (if π- and σ- refer to p- and s-polarized) you would use a 1/2 wave plate, not a 1/4-wave plate.

Hi

What I meant was tbat B points along some direction I call z. My laser propagates along z too, and it is linearly polarized perpendicular to z. I want to convert this linear polarization to σ+ (wrt. to z).

lambda/4 wave plates should have some indication where the fast and the slow axes are. The orientation relative to the (linear) polarization of incoming light will determine how the polarization afterwards looks like.

Hi

Thanks for that.

 

[sardar]

Hi Niles,

Great question! Lambda-quarter plates are used to convert linearly polarized light into circularly polarized light. The polarization direction of the circularly polarized light depends on the orientation of the quarter plate's fast axis relative to the incident polarization. In optics, the fast axis is typically marked on the quarter plate itself, so you can align it accordingly.

To determine whether the quarter plate will produce σ+ or σ- polarization, you can use a polarizer and a quarter wave plate together. First, rotate the polarizer to allow only σ+ polarization to pass through. Then, place the quarter wave plate between the polarizer and the light source. If the light passing through the quarter wave plate is completely blocked by the polarizer, then the quarter plate is producing σ+ polarization. If some light is able to pass through the polarizer, then the quarter plate is producing σ- polarization.

Alternatively, you can also use a detector, such as a photodiode, to measure the intensity of the light passing through the quarter plate. By rotating the quarter plate and measuring the intensity, you can determine whether it is producing σ+ or σ- polarization.

I hope this helps clarify the process for determining the polarization produced by lambda-quarter plates. Happy experimenting!