I’m reading Uncle Tungsten by Oliver Sacks, which is a sort of young-boy-discovers-the-joys-of-science autobiographical work. In one chapter, the author mentions in passing that a magnetic field will affect polarized light, but doesn’t go into details. Just what effect does a magnet have on polarized light? And why does it do so?
It’s called the Faraday effect.
cheap link:
http://www.minidisc.org/eb/faraday_effect.htm
-Luckie
The magnetic field doesn’t directly affect the light. It affects the polarization currents in the material the light is passing through. With a magnetic field parallel to the direction of travel of the light, the charges will be displaced perpendicular to the plane of polarization, and will add a component of the other polarization. In a vacuum, the Farady rotation should be zero.
If the magnetic field is perpendicular to the polarization and propagation directions, the displacement due to the magnetic field is in the direction of travel, so this won’t affect the polarization. If the magnetic field were parallel to the electric field direction, no displacement due to the magnetic field would occur.
Luckie and ZenBeam have already said the obvious thinhs I was gonna say, but just for the sake of completeness, the magnetic field affects the medium through which the light is passing, not the light itself. (since the light wave and the field are both electro-magnetic phenomena, an electric or magnetic field directly interacting with a photon would be required. The probability is non-zero, but way low, and AFAIK has never been observed).
There are other magneto-optical effects related to polarization. The Kerr Magnetic Effect (not to be confused with the more common Kerr Electro-Optic Effect) causes the polarization of light reflected from the polished pole face of an electromagnet.
I also note that when you place your radiating atoms in a magnetic field, you split the level degeneracy and the different lines have different polarizations, the * Zeeman Effect*