Notes on the Kerr Effect

A glass box containing a certain liquid (such as nitrobenzene) is called a Kerr box. A parallel plate capacitor is installed in the box, and a transverse electric field is generated when a voltage is applied. The Kerr cell is placed between two crossed polarizers. When there is no electric field, the liquid is isotropic and light cannot pass through P2. When an electric field exists, the liquid has the properties of a uniaxial crystal, and the optical axis is along the direction of the electric field. At this time, light passes through P2 (see interference of polarized light). Experiments show that under the action of an electric field, the difference in principal refractive index is proportional to the square of the electric field intensity. When the electric field changes, the light intensity passing through P2 changes accordingly, so the Kerr effect can be used to modulate light waves. Liquids are polarized under the action of an electric field, which is the cause of birefringence. The polarization effect of the electric field is very rapid. The polarization process can be completed in less than 10-9 seconds after the electric field is applied. After the electric field is removed, it becomes isotropic again in the same short time. This rapid action property of the Kerr effect can be used to create an almost inertial light switch: a light gate, which has found important applications in high-speed photography, light speed measurement and laser technology.