# Polarization

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Definition:

Reflection of a plane wave from a surface perpendicular to the page. The p-components of the waves are in the page, while the s components are perpendicular to it.

rpar=(tan^2(alpha-beta)/tan^2(alpha+beta)

rperp=(sin^2(alpha-beta)/tan^2(alpha+beta)

alpha=angle of incedence beta=transmitted angle

## Contents

S-Type

### P-Type

P-Type Polarizaton

P-Polarization is used when you need to minimize the reflection off an interface between two materials of differing index of refraction. The index of refraction of air is about 1 and most glasses are about 1.5.

For these two the angle of least reflection is about 56 deg. and is known as the Brewster's Angle.

### Finding P-Type Polarization

One way to determine p-polarization is to set up your plateholder at Brewster's Angle (about 56 deg) and place a single piece of glass in it. Hit the glass with your spread beam. The glass is going to reflect some of the light hitting it, so place a white card in this reflected light path (in order to view it). If you rotate your laser head, you will notice that this reflected light becomes brighter and dimmer. Find the spot within the rotation where the reflected light is at it's dimmest on your white card, and you've got it. There should be two spots for this with every 360-degree of rotation. With a HeNe, you'll always have a "little" bit of light reflected. With a properly-running diode, the reflection will go completely out on the card (100% -- or VERY close to 100% -- transmission through the glass).

### Finding S-Type Polarization

The easiest way to find S-Type Polarization is to find P-Type first and mark the top of your laser. Rotate the laser 90 degrees and you are at S-Type.

Another method is to make a set up like for finding P-Type Polarization and place a light meter in the reflected beam. Adjust the rotation of the laser until the reflected light is a maximum.

### Testing Materials for Bifingence

Many plastics will act as a bad wave plate. They will take your linear polarized laser beam and make it elliptical. Fortunatly there is a easy way to check. Place the sample of the material in question in between two crossed polarizers. If you see colors then it is acting to rotate the polarization.