The
Pockels effect (after
Friedrich Carl Alwin Pockels who studied the effect in 1893), or Pockels electro-optic effect, produces
birefringence in an optical medium induced by a constant or varying
electric field. In the Pockels effect, also known as the linear electro-optic effect, the birefringence is proportional to the electric field. In the
Kerr effect, the refractive index change (birefringence) is proportional to square of the field. The Pockels effect occurs only in crystals that lack
inversion symmetry, such as
lithium niobate or
gallium arsenide and in other noncentrosymmetric media such as electric-field poled polymers or glasses.