Optical Kerr Effect

The third-order nonlinearity can lead to an intensity-dependent refractive index known as the optical Kerr effect. With ω₂ = −ω₁, to
...... (1)
where E_av is the average electric field strength. The tensor χ⁽³⁾ describes the effect of an intense light beam upon the propagation path of the beam. The selfinduced effect manifests itself as an intensity-dependent contribution to the index of refraction
 ..........(2)
The effect of an intensity-dependent refractive index is exploited in Kerr lens mode-locking (KLM). In high-intensity beams the nonlinear refractive index can be the source of optical damage because it can lead to self-focusing and small-scale ripple growth.