High-resolution magneto-optic measurements with a Sagnac interferometer (invited)

A technique for measuring the Faraday effect and the magneto-optic Kerr effect has been developed. In a Sagnac interferometer, two optical beams follow identical paths in opposite directions. Effects which break time-reversal symmetry, such as magneto-optic effects, will cause destructive interference between the two beams. By measuring the phase shift between circular polarization states reflected from a magnetized sample, the polar magneto-optic Kerr effect is measured to an accuracy of 3 prad, with a spatial resolution of 2 pm. The interferometric technique provides a number of advantages over conventional polarizer methods, including insensitivity to linear birefringence, the ability to completely determine the magnetization vector in a region, and the ability to sensitively measure magneto-optic effects without an external field. It is also shown that this device has great potential if incorporated into a near-field optical device. Some of the considerations for the design of a near-field Sagnac magneto-optic sensor are introduced and the advantages of the device are discussed. Some preliminary experiments are shown.