# Polarization of light

1. Feb 25, 2015

### Jimmy87

Hi pf, I am trying to find answers to the following two questions about polarization of light but am struggling to find anything:

1) When unpolarized light strikes the surface of water, some of the reflected light is horizontally polarized. I was trying to find out what causes this to happen. From other threads I have an idea. Is it because the electric dipoles in the water oscillate when they absorb the incoming light. Since they are constrained to oscillate along the plane of the water surface the re-radiated light must be polarized in this direction? If this is right, then I thought dipoles could radiate EM radiation in any direction so long as it isn't along the top or bottom of the dipole. This would give a whole range of directions to radiate from the surface would't it?

2) Polaroids consist of stretched polymers that absorb light polarized in the same direction as the polymers are arranged. What is the mechanism behind how they are absorbed like this?

Any help or links to resources is greatly appreciated!

2. Feb 25, 2015

### Staff: Mentor

3. Feb 26, 2015

### blue_leaf77

1) The dipoles do radiate approximately isotropically, but only in the direction along the reflection angle specified by Snell's law waves from different dipoles interfere constructively.

4. Feb 26, 2015

### clem

The Fresnel relations in optics show how polarization happens. It is not due to individual dipoles.
Look for "Fresnel relations" in the index of any general physicsor optics textbook.
They show that horizontal polarization is reflected more strongly than vertical polarisatiion.

5. Feb 26, 2015

### aabottom

1) When unpolarized light strikes the surface of water, some of the reflected light is horizontally polarized.

A good model- the boundary conditions of Maxwell's equations [1] of plane waves incident on a dielectric interface, e.g. air/ water boundary. At Brewster's angle, the reflected wave is completely polarized so that the E-Field is parallel with the surface interface (what is called s-polarized) [2].

[1] http://physicspages.com/2014/09/02/maxwells-equations-in-matter-boundary-conditions/
[2] http://en.wikipedia.org/wiki/Fresnel_equations