Kerr effect

Summary

The Kerr effect is a change of the refractive index of a medium proportional to the square of an applied electric field. In the electro-optic form the field is a static or slowly varying field, and it makes an isotropic medium birefringent. In the optical form the field is that of the light itself, so the index depends on the intensity: $n = n_0 + n_2 I$. The optical Kerr effect comes from the third-order nonlinear susceptibility and causes self-focusing, self-phase modulation and optical solitons.