MEASUREMENT OF MAGNETIC-FIELDS USING THE MAGNETOOPTIC KERR-EFFECT

A technique for measuring small magnetic fields using a thin amorphous magnetic film and the magneto-optic Kerr effect has been developed. A thin film having in-plane uniaxial anisotropy is aligned such that an external magnetic field rotates the film magnetization in a controlla ble manner. This magnetization rotation is ''read'' optically by a coh erent homodyne measurement of the amount of polarization rotation caus ed by the magneto-optic Kerr effect during reflectance of polarized li ght from the film surface, using one polarization as the local oscilla tor. The resulting signal is linear in magnetic field. Initial noise e quivalent magnetic field sensitivity measurements of the technique yie ld 2 mOe/Hz 1/2 at a frequency of 8 mHz. Calculations indicate that se nsitivities of order 10(-6) Oe/Hz 1/2 are obtainable using this techni que.