Magnetooptic

Magnetooptic refers to the interaction of magnetic fields with light in which a material's optical properties depend on its magnetization, or light influences magnetization. The most studied effect is the Faraday effect: the polarization plane of linearly polarized light rotates as it propagates through a magnetized material. The rotation angle is proportional to the path length and the magnetic field, quantified by the Verdet constant.

In reflection, the magneto-optic Kerr effect produces rotation and ellipticity changes of the reflected light. These effects rely on magnetization breaking time-reversal symmetry and are used to control polarization in devices in a nonreciprocal manner.

Common magneto-optic materials are ferrimagnetic garnets such as yttrium iron garnet and bismuth-substituted iron garnets; they are highly transparent in the visible and near-infrared and offer large Verdet constants. Other materials include ferrites and certain doped oxides, as well as some semiconductor alloys.

Applications include non-reciprocal optical components such as Faraday isolators and circulators for fiber-optic communications, magneto-optic modulators and spatial light modulators, and magneto-optical data storage media, where information is written magnetically and read optically. Magnetic-field sensing and imaging also exploit polarization changes induced by magneto-optic effects.

The field originated with Faraday's 1845 discovery of light rotation by a magnetic field; the Kerr effect was described in 1875 and has informed many modern devices and materials research.