Materials for third-order nonlinear optics

This article provides a brief introduction to third-order nonlinear optical materials, including both the real and imaginary components, and is intended to be a personal perspective of the field. It describes applications that can be enabled by molecules with large two-photon absorption (2PA) cross sections and how symmetrical donor-(pi-bridge)-donor molecules exhibit large cross sections associated with significant changes in quadrupole moment between the ground-and first-excited electronic states. The application of such materials for 2PA three-dimensional microfabrication is described. The article then turns its focus to materials for all-optical switching applications and explains how cyanine-like molecules can be developed to have both very large real third-order nonlinear coefficients and small 2PA cross sections, both of which are necessary for efficient all-optical switching materials.