What is magneto-optical Kerr effect?

Kerr effect 1875 British physicist J. Kerr found that glass plates have birefringence under the action of strong electric field, which is called Kerr effect. Later, it was found that many liquids and gases can produce Kerr effect. The experimental device for observing Kerr effect is shown in the figure. A glass box containing a certain liquid (such as nitrobenzene) is called a Kerr box. The box is equipped with a parallel plate capacitor, which generates a transverse electric field after voltage is applied. Kerr cell is placed between two orthogonal polarizers. When there is no electric field, the liquid is isotropic and light cannot pass through P2. In the presence of electric field, liquid has the property of uniaxial crystal, and the optical axis is along the direction of electric field. At this time, the light passes through P2 (see interference of polarized light). Experiments show that under the action of electric field, the difference of principal refractive index is directly proportional to the square of electric field intensity. When the electric field changes, the light intensity passing through P2 also changes, so the Kerr effect can be used to modulate light waves. Liquid is polarized under the action of electric field, which is the reason of birefringence. The polarization of the electric field is very rapid, and the polarization process can be completed in less than 10-9 seconds after the electric field is applied, and it becomes isotropic in the same short time after the electric field is removed. The fast-acting characteristics of Kerr effect can be used to make an optical switch-optical shutter with almost no inertia, which has been widely used in high-speed photography, light speed measurement and laser technology.