Hyperpolarizability

Hyperpolarizability is a measure of a material's non-linear optical properties, specifically its response to an applied electric field in a way that goes beyond the linear (first-order) response. In simpler terms, while linear polarization relates to how a material's electric dipole moment changes in proportion to an applied electric field, hyperpolarizability describes how the dipole moment changes in response to higher-order terms of the electric field.