• KFC
In summary, The text explains polarization as how the light oriented. A linear polarization means the light is oriented on one direction. However, the electric fields in circular polarized light are not always moving at the same speed, which creates a lag. Circular polarized light is reflected by a mirror in the same way, but the direction of the circular polarization is opposite.
KFC
Hi all,
To me, polarization is the most confusing concepts in optics to me. From the text, it is said that polarization is how the light oriented. A linear polarization means the light is oriented on one direction. But I have few doubts I learn from the book and online materials

1) In most book and some youtube material, it is said that a linear polarizer is used so an unpolarized light only have one orientation of the light can pass through. My understanding is an unpolarized light has components of all direction. Even some components is not along the transmission direction of the polarizer, but those components could have some projection along the transmission direction. So basically, all components oriented at any direction could pass the liinear polarizer but some direction will all go through some will just a bit, depends on the projection. Is that correct?

2) In wiki (https://en.wikipedia.org/wiki/Linear_polarization), it explains the linear polarization as linear-polarized along a plane consisting of two orthogonal, in-phase components. My first question is why there will be two components of the electric field? I know electric field component is a vector so it could decomposed into any two components, is this the reasoning why there are two components? If so, can I say linear polarized light is the electic field oriented a specific direction which doesn't not change in time so the decomposed two components are always in-phase?

3) I read a video in youtube about circular polarization. The guy explain that a circular polarization means two components of the electric fields are not moving at the same speed, one is lag by 1/4 wavelength than the other, so the tip of the synthesized electric field vector is along a helix. If we view from the direction of propagation, we see a circle. Am I understand this correctly?

4) I remember I read it somewhere about circular polarized light reflected by a mirror, will the direction of circular polarization opposite if we use a mirror to reflect the light in circular polarization? For example, if we have a clockwise circular polarized light inject into a mirror making 30 degree to the light, will the reflected light becomes counterclockwise circular polarized? why?

5) the last question is about how to check the circular polarization in experiment. I read this online, someone use a quarter-wave plate and a beam splitter cube. Passing the circular polarized light to the quarter-wave plate and left the outgoing light through the beam splitter, the component perpendicular to the direction of propagation should be zero if the incoming light is circular polarized, why is that?

Sorry for the long question. I am trying to collect as much information as I can to understand the light polarization, I just want to confirm with someone here that my understanding is correct or not.

1) Yes that's correct.
KFC said:
can I say linear polarized light is the electic field oriented a specific direction which doesn't not change in time so the decomposed two components are always in-phase?
2) That's why it's called linear polarization. In general, 180 degree phase difference also amounts to linear polarization.
KFC said:
The guy explain that a circular polarization means two components of the electric fields are not moving at the same speed,
3) Probably you have misunderstood what you have heard from that source. As long as there is no birefringence in the medium through which the light propagates, both the x and y components travel with the same speed. One component only lag from the other. If you imagine you can see the tip of the vector, yes it should look like a circle.
4) If you are being consistent in defining what you call CW or CCW (i.e. if you see the incoming wave by facing it head on then you should also see the reflected one by facing it head on), both the incoming and and reflected waves should have identical polarization state. Note that reflection in general might change the state of polarization as Fresnel formulae for reflectance tell us that the reflection coefficients for the TE and TM components generally differ.
5) Would be better if you provide the link.

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KFC said:
I guess this one?

KFC said:
The guy explain that a circular polarization means two components of the electric fields are not moving at the same speed, one is lag by 1/4 wavelength than the other,
Differential speed is only used to create the lag. After passing the quarter-wave plate the components have the same speed again, but retain the λ/4 phase shift.

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blue_leaf77
KFC said:
4) I remember I read it somewhere about circular polarized light reflected by a mirror, will the direction of circular polarization opposite if we use a mirror to reflect the light in circular polarization? For example, if we have a clockwise circular polarized light inject into a mirror making 30 degree to the light, will the reflected light becomes counterclockwise circular polarized? why?
The clockness is defined wrt to the propagation direction, which swaps during reflection.

KFC said:
5) the last question is about how to check the circular polarization in experiment. I read this online, someone use a quarter-wave plate and a beam splitter cube. Passing the circular polarized light to the quarter-wave plate and left the outgoing light through the beam splitter, the component perpendicular to the direction of propagation should be zero if the incoming light is circular polarized, why is that?
Passing circularly polarized light through a quarter-wave plate will make it linearly polarized, which can be identified with a linear polarizer at different angles.

A.T. said:
The clockness is defined wrt to the propagation direction, which swaps during reflection.
Upon checking in my textbook, that seems to be true and the reason is that because the reflection coefficients for the TE and TM have opposite sign. This actually have been puzzling me for a while because for normal incidence how could we tell which component should be TE or TM?

## 1. What is polarization?

Polarization refers to the orientation of the electric field in an electromagnetic wave. In an unpolarized wave, the electric field oscillates in all directions perpendicular to the direction of propagation. In a polarized wave, the electric field oscillates in only one direction.

## 2. What is a polarizer?

A polarizer is a material that selectively allows certain orientations of the electric field to pass through, while blocking others. This results in the polarization of light passing through the polarizer.

## 3. How does polarization occur?

Polarization occurs when light waves interact with certain materials or structures, causing the electric field to become aligned in a specific direction. This can happen through reflection, scattering, or transmission.

## 4. What is the difference between linear and circular polarization?

Linear polarization occurs when the electric field oscillates in one direction, while circular polarization occurs when the electric field rotates in a circular motion. Linear polarization can be thought of as a special case of circular polarization, where the rotation is along a straight line instead of a circle.

## 5. What are some applications of polarization?

Polarization has various applications in science and technology. It is commonly used in photography, 3D movies, and sunglasses to reduce glare and improve image quality. It also plays a role in optical communication, where polarized light is used to transmit data. In addition, polarization is important in various scientific fields such as astronomy, materials science, and biomedicine.

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