Kerr effect

Kerr effect is a phenomenon occurring in almost all isotropic transparent substances when they are under the influence of a magnetic field: in this case, they suffer a variation of their optical properties and become birefringent. This behaviour is like that of a single-axed crystal with optical axis parallel to the electric field. A typical application of this effect is Kerr cell. It consists of a capacitor with dielectric placed between two crossed polarizers. If no electric field is detected across the capacitor plates, the intensity of the wave sent by the second polarizer is equal to zero. Applying a voltage will create an electric field across the capacitor plates, and a phase shift is induced on the wave. The wave will be biased elliptically at the cell output and the second polarizer will send only the component parallel to its own optical axis. This experiment enables to assess Kerr effect in a solution of nitrobenzene. A small vessel of glass including a plate capacitor is filled with liquid. This vessel is kept between two filters arranged at 90°. In the beginning a dark field will be displayed on the screen, but after the application of an electric field, the displayed field will become clearer, because the light beam is electrically biased when crossing the birefringent liquid.