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Question regarding polarisation Answered

Hi guys!

Can someone describe me,in simple terms, what exactly is polarisation(Specifically of light)? I am a little confused on this topic.  And how many types of polarisation are there exactly? I mean is polarisation exclusive to optics or is it seen even other fields? 

(P.S. Dr.Kelsey, i know you are here somewhere, you raised doubts regarding this topic in my previous question, so i'm sure you will provide answers too this time :) :D)


ok so simply i ca put it like this:
light is a transverse wave in that it oscillates at 90 degrees to the direction of travel of the light beam. polarised light contains only photons that are oscillating in the same direction so for example only vertical waves. a polariser is a piece of equipmet that blocks all light not polarised in a specific direction.

Photons don't oscillate. The classical electric and magnetic fields oscillate, at 90 degrees to each other and to the direction of propagation.

Photons individually carry angular momentum, with a spin axis oriented perpendicular to the photon's momentum direction.

Let's start at the beginning. For the simplest, pure electromagnetic wave (whether light, or radio, or x-rays, or whatever), the electric and magnetic fields both oscillate in a plane, perpendicular to each other and perpendicular to the direction the wave is moving (for example, if the wave is moving along +Z, then the electric field might be along +/-X and the magnetic field along +/-Y). That wave is called plane polarized, because each field (usually the electric field is what is discussed, because the magnetic field is always perpendicular to the electric field) is restricted to a plane.

When you turn on a light, or an LED, or even a laser, the light beam you see is made up of bazillions of separate waves, all travelling in more or less the same direction. But each one has its electric field in a different direction, some are along X, some along Y, some at all the angles between X and Y. That light is unpolarized.

If you pass unpolarized light through a special filter, or through certain minerals, or reflect the light off of a mirror surface, only those waves with the electric field aligned in a specific direction will be let through. That is how you can make a plane-polarized beam.

In addition to plane polarization, there is also circularly polarized EM beams. Take two pure light waves of exactly the same frequency, one with the electric field along X and one with the field along Y. If the two waves are exactly in phase, the fields (the planes of polarization) will add up to a net field along the 45-degree line between X and Y, still plane polarized.

But if the two pure waves are 90 degrees out of phase, then when the X wave is at a maximum, the Y wave will be zero, and vice versa. If you add the two fields for each instant of time, you see that the resultant polarization vector traces out a circle, either clockwise or counterclockwise (depending on whether the phases are +90 or -90 degrees). This is circular polarization.

When radio signals are generated, they are almost always polarized right from the beginning. That's because you make radio waves by getting electrons to oscillate back and forth in a long straight wire. Since they're moving in a straight line, the EM wave has an electric field confined to that plane, and is therefore plane polarized.

Ah, thanks again for the simple explanation Dr.Kelsey! So, as far as i understand, it is only limited to EM waves, correct?

Well, "limited to EM" sort of depends. EM waves are the most common sort of thing we observe, so in that sense, yes.

However, you can build models to demonstrate polarization with other things. For example, you can use a long rope anchored at one end. When you wiggle the free end up and down you make transverse plane-polarized waves in the rope.

I think you are looking for polarization with z.. If so, start here http://science.howstuffworks.com/innovation/everyday-innovations/sunglass6.htm

Then here http://en.wikipedia.org/wiki/Polarization_(waves)

That should help.

It's a "z" in the US, but the author speaks English


Ah... I really had no idea. Sorry about that!

Oh yes, we follow the British system, so to be true to it and not mix stuff up, i used it. Although i have no problem using Either US or UK version, as long as i can convey my message properly. :)

If you have "poles", then you have alignment and direction. Polarisation is a term which describes things as being directional or being in directional positions.

In light-terms you have electromagnetic-conformity, where light has a particular "direction" attached to it, so polarised-filters can either block or pass it (according to their polarisation / directional-bias.