# Homework Help: Polarization question

1. Aug 15, 2008

### Vanush

Hi all.. I don't understand polarisation.

When unpolarised light is passed through a polarizer, the result is linearly polarised light with the E field oscillating in a direction parallel to the transmission axis of the polarizer. Say it passes through another sheet (analyzer) with its transmission axis at an angle theta to the transmission axis of the polarizer, then 'the component' of light parallel to the analyzer's transmission axis then let through.

What I don't get is.. Havent you already extracted a certain E-field direction from the light when you let it through the polarizer.. How can it have more components (which the analyzer 'extracts')??

Similarly, when linearly polarized light is passed through birefringent material, it still splits in two?? ie waveplate theory..

2. Aug 16, 2008

### merryjman

You are right that the first polarizer has selected a direction for the light that passes through. But if the second polarizer is at an angle relative to the first, then the light's E-field direction will have both X- and Y- components when it reaches the second. I can call my vector (1,0) if I want, but if I rotate my frame of reference 90 degrees, now my vector is (0,1) isn't it? And in a third reference frame, this vector could be (0.7,0.7) couldn't it? Do you see the analogy?

Birefringent materials are more complicated, because they don't refract light in a linear isotropic fashion the way ordinary materials like glass and plastic do. In some directions light will refract a lot more than others. So for certain orientations of the birefringent crystal, you will have two beams - one that was refracted in the ordinary manner, and one that was refracted in the extraordinary manner.