Friday, August 29, 2008

Day 11 On Polarization

One of the key aspects of this experiment is polarization. We use polarization in our experiment for two things: decreasing the amount of light (also called attenuating the light), and forcing the light to take one instead of both possible paths. Today we took a break from data collection to reflect on polarization.

Polarization is the shape of the electrical fluctuation. This means if somehow you could take a picture of light as it travels towards you, the shape that you would see is the polarization. Another explanation is with a jump rope. Imagine a jump rope tied to a tree, if you twirl it you will see the circular "polarization" of the rope. To understand a polarizing filter think of a frictionless picket fence between you and the tree with the rope in between two slats. When you twirl the rope it is circularly polarized between you and the fence. Between the fence and the tree it is vertically polarized. The fence is acting as a vertical filter; it only allows vertical waves to pass through. Now lets rotate that filter to horizontal. Again, the shape of the waves in the rope from you to the fence remain circular, but this time the shape from the fence to the tree is horizontal. You can rotate the fence to any angle and make any linear polarization. In this experiment, our "fence" is a linearly polarized camera filter and our "rope" is the laser light.

Circular polarization filters are more difficult to imagine. They do the same thing as a linear filter except they only allow circular waves to pass through. Unlike linear filters, rotating a circular filter will not change the filter polarization because a circle rotated is still a circle. Even so you can get two polarizations out of a circular filter by flipping it over. This creates right hand circular on one side and left hand circular polarization on the other.

These are some representations of various polarizations.

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