Polarizer Setup: How Does Rotating Change Polarization?

[scarecrow]

http://img338.imageshack.us/img338/9050/polarizerya6.jpg

I apologize for my bad sketch.

Hi,

I need help understanding how this setup changes the polarization of the outgoing beam if the entire setup is rotated.

There are 3 mirrors (gold): 2 mirrors are adjacent and set at 30 degrees, and the third mirror is directly centered above the first 2 mirrors. The laser beam strikes the first mirror (left) at the center, then strikes the center of the top mirror, and finally propagates to the third mirror and gets reflected out.

The laser beam I'm using to test this home-made polarizer is a basic HeNe laser.

Question: How can an incident unpolarized light become polarized outgoing by rotating the entire setup? (All three mirrors are connected to the same aluminum module).

I can only see how POLARIZED (s or p) light can work with this setup, but not unpolarized light. Is the laser beam in fact polarized?

Thanks.

 

[Meir Achuz]

Reflection partially polarizes light perpendicular to the plane formed by the incident and reflected beam.

 

[astrokreng]

Hello,

Thank you for your question. The polarizer setup you have described is known as a Brewster's angle polarizer. This setup works by using the reflective properties of the mirrors to filter out light that is polarized in a certain direction.

When light is incident on a surface at a specific angle, known as the Brewster's angle, the reflected light will be completely polarized in the plane of incidence (the plane that contains both the incident and reflected light rays). This is due to the fact that at this angle, the electric field of the incident light is parallel to the surface of the mirror, and therefore only the component of the electric field parallel to the surface is reflected.

In your setup, the first mirror is set at a 30 degree angle, which is close to the Brewster's angle for the laser light. This means that the reflected light from this mirror will be mostly polarized in the plane of incidence. The second mirror, which is set directly above the first mirror, acts as a polarizer for this polarized light. The third mirror then reflects this polarized light out of the setup.

When you rotate the entire setup, you are changing the angle of incidence of the laser light on the first mirror. This means that the angle at which the light is polarized will also change, and therefore the polarization of the outgoing beam will change as well. If you rotate the setup to a different angle, you may find that the outgoing beam is no longer polarized.

As for your question about the incident light being polarized, it is possible that the laser beam is already polarized. Many lasers emit light that is already polarized, but it is also possible for the laser to emit unpolarized light. Either way, the setup will still work to polarize the light further.

I hope this explanation helps to clarify how rotating the setup changes the polarization of the outgoing beam. If you have any further questions, please feel free to ask.