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Faraday Rotation in Optical Media

The optical rotation of light by a refractive medium in a magnetic field was first discovered by Michael Faraday in 1845. The effect, like the optical rotation induced by chiral organic molecules, is due to circular birefringence, the difference in propagation velocities for light of opposite circular polarizations. Since atomic states are weakly perturbed by magnetic fields, the changes in the optical refraction indices are of the order of one part per 105 but this effect is exquisitely sensitive to quite small shifts in atomic energy levels. Typical angles of optical rotation are of the order of tens of degrees. In this experiment, you will measure the Faraday Effect for two different media and four different wavelengths of light and show that the rotation angle is linearly proportional to the magnetic field integral parallel to the light propagation direction.

During the workshop, the following topics will be covered:

  1. Overall description and examination of the Faraday rotation experimental apparatus
  2. Elementary discussion of the atomic physics that describes the effect
  3. Construction of the high field magnet assembly from basic parts
  4. Measurement of the longitudinal magnetic field distribution along the symmetry axis
  5. Measurement of the Faraday rotation for two glasses, BK-7 and SF-57, at four wavelengths
  6. Measurement of the Faraday rotation for SF-57 as a function of the magnetic field integral
  7. Comparison of the observed rotation of linear polarization with predictions based on the refractive indices of the glasses
  8. Discussion of the Faraday effect from a quantum mechanical viewpoint

One of the unusual aspects of this experiment is the relatively large axial magnetic field produced by a cylindrical cluster of rare earth permanent magnets which render a high current power supply superfluous. Workshop participants who are interested in acquiring this experiment for their home institution are invited to purchase in advance the permanent magnets and associated parts that will be assembled during the workshop. It is estimated that these components will cost about $1000 per set and you will have the option of choosing to order these prior to the workshop.

Participants are urged to bring a laptop and a notebook.

The cost of the Faraday rotation experiment is approximately $2500 not including the DVM shown on the left. This includes four different laser light sources and three different glass samples (BK-7, N-SF-57 and N-SF66). The components fabricated in our departmental machine shop cost about $975 and are included in that total. If you would like to purchase and assemble these items which generate a 1 kGauss field over the samples, you can arrange this by communicating in advance with Ramón Torres-Isea or Carl Akerlof.