Course:Polarization

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The following topics should be fully understood before studying this article.



Main article: polarization

Polarization is a concept that is fairly easy to comprehend. It plays a key role in many concepts and instruments that are important to gemologists. Understanding the basics of polarization is vital in your studies.

For this discussion we are going to regard light as traveling in waves, much like ocean waves. While ocean waves mainly go up and down, in light the waves can vibrate in any direction.
If we were to isolate a single light wave, it could vibrate up and down (North-South), from the left to the right (East-West) or vibrate in any direction between those two.
Important to understand is that a single light wave will vibrate only in one plane, like up and down or any other direction. No matter which direction that is. When this happens (and it always does), we say that the light wave is polarized.

Unfortunatly light never travels alone, but in endless bundles of an infinite number of lightwaves. All of these lightwaves vibrate in different directions and the result is unpolarized light. Light coming from the sun or a lightbulb is always unpolarized.

Polarized light is light made up of lightwaves that all vibrate in the same direction
A single lightwave which vibrates North and South


To visualize this, you can imagine a skippy rope held by two people on opposite ends. If one of them would move his hand up and down fast, the rope will form waves going from one person to the other. The produced wave vibrates up and down (or better "North-South").
Similar if someone would move their hand left to right, the rope will vibrate like a snake (left to right).
You can move your hand even diagonal and the result will be a wave that vibrates diagonaly.

When we say that a wave vibrates in the up and down direction, those are actually 2 directions; one up and one down. So it is better to talk about the plane in which it vibrates. So the virbrational plane is in this case in the North-South directions. Or even better; the lightwave is polarized in the North-South plane.

As said before, light is made up from an infinite number of those polarized lightwaves and some travel in the same plane while many others vibrate in a random other plane. In the images below, a maximum of 4 lightwaves are illustrated and distinguishing them is already becoming difficult. Drawing a million of them would not even come close to reality, so you will have to use some imagination.

3-dimensional illustrations of polarized and unpolarized light
Polarized North South.jpg Polarized east west.jpg Unpolarized.jpg Unpolarized complex.jpg
lightwave vibrating in the North-South plane (polarized) lightwave vibrating in the East-West plane (polarized) light made up from two lightwaves, each vibrating in a different plane (unpolarized) light made up of four lightwaves, all vibrating in a different plane (unpolarized)

At this point it should be mentioned that the colors used in the illustrations are for illustration purposes only, so don't start thinking that all red light vibrates in the North-South plane. Some red lightwaves might, but not all do. It's random.

In gemology (and many other sciences) we sometimes want light to be polarized, that is we want light that only vibrates in a certain plane (like the North-South plane). In order to do that we must "block" all the light waves that do not vibrate in the desired direction.
For this purpose polarization filters were invented by Edwin Land (whom started the Polaroid Corporation).


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