The Pockels effect, or Pockels electro-optic effect, is the production of birefringence in an optical medium induced by a slowly-varying electric field. It is distinguished from the Kerr effect by the fact that the birefringence is proportional to the electric field, whereas in the Kerr effect it is quadratic in the field. The Pockels effect occurs only in crystals that lack inversion symmetry, such as lithium niobate or gallium arsenide.
The Pockels effect is used to make Pockels cells, which are voltage-controlled wave plates. In combination with a polarizer, this can be used to create a fast shutter which can open and close in nanoseconds. These are used in a wide variety of scientific and technical applications.
Friedrich Carl Alwin Pockels studied the effect, which bears his name, in 1893.