Kerr Nonlinearity via Cascaded Optical Rectification and the Linear Electro-optic Effect

We show both theoretically and experimentally that the combined processes of optical rectification and the linear electro-optic effect lead to an effective nonlinear refractive index $n_2$ in noncentrosymmetric materials. This cascaded second-order nonlinear optical effect arises in addition to the well-known contribution due to second-harmonic generation and difference-frequency mixing and is of comparable magnitude. However, it has the advantage of a broad acceptance angle because no precise phase matching is needed. Experimental results in KNb${\mathrm{O}}_3$ crystals are presented.