Pulsed Faraday Rotation

Faraday Rotation is a phenomenon showing that magnetism and light are related. This is accomplished by demonstrating that the polarization properties of a medium are affected by the presence of a static magnetic field (B). Although the rotation of the plane of polarization of light by a modest B field is typically a small effect, this variant of Pulsed Faraday Rotation uses an ordinary (and commercially available) apparatus together with a new prototype pulsed-current supply to excite the solenoid. The use of brief (<10 ms) pulses allows the solenoid to be exposed to currents with peak values near 50 A, which is about 10 times larger than any steady current that could safely be used with the solenoid. Faraday rotations of more than 45 degrees are readily obtained. This effect is used in the design and description of Faraday isolators. Students using this sort of apparatus learn how electrical energy can be capacitively stored and then safely discharged in brief high current pulses. They learn techniques of data acquisition for brief single events, including the art of triggered acquisition. They learn two independent techniques for quantifying pulsed large magnetic fields, and they learn the modelling required to interpret experiments in the transmission of polarized light to infer instantaneous Faraday rotation.