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 arsenideand in other noncentrosymmetric media such as electric-field poled polymers or glasses.

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