Faraday Effect

Published on: Thu Jun 02 2011

The more I read about entanglement and single photon detectors, the less I think it would make a good summer project. I'd probably spend two weeks just setting up the equipment. But while reading about BBO crystals I was reminded of a report I wrote for PHY 307 on Faraday, one of his discoveries was the Faraday effect. The Faraday effect seems like something I could investigate over the summer.

The Faraday effect causes left and right circularly polarized waves to propagate at slightly different speeds. It occurs in optically transparent dielectric materials. This definition is a bit strange, because the definition of dielectric is an electrical insulator than can be polarized by an applied electric field. I'm reading from wikipedia, perhaps it is not correct here, because an applied electric field means what? Imagine placing a dielectric material between two capacitor plates, in the static e-field. Current does not form in the insulator, but the equilibrium of the charge distribution is disturbed.

What is happening here, is that a dielectric material becomes polarized in an electric field, but in a magnetic field the light becomes polarized? If I take a transparent dielectric material and shine a linearly polarized laser through it, then measure the polarization afterwards, the polarization should still be the same. Then if I place the dielectric crystal into a electric field and shine the linearly polarized laser through it, I should be able to filter out some of the light (if I wanted to rotate my dielectric polarizer, should I rotate the e-field?). Finally if I place the dielectric crystal into a magnetic field, I should measure a circular polarization to the outgoing light? Isin't the E-field generating a B-field? So I can't separate the two, but I think I need a stronger B-field.

So, for the first week of the summer program I would be investigating the Faraday Effect. Perhaps a quick write up on dielectric materials, and measurements of the Verdet constant of different materials in the lab.

I found an article on Faraday rotators, and it mentioned a very important detail. If I send light through a Faraday rotator, then reflect it back through again, it does not cancel itself out, instead it rotates it again. The direction does not matter. This is why a Faraday rotator is different than a half-wave plate. The wikipedia article on Faraday effect notes that Faraday rotators are used for amplitude modulation.

There are also Faraday Isolators.