Third-Order Nonlinear Optical Response of Some Tetrasubstituted Cumulenes

Third-order nonlinear optical properties of several tetrasubstituted cumulenic compounds were studied using subpicosecond degenerate four-wave mixing (DFWM) in the forward geometry. Mean values of the second molecular hyperpolarizability 〈γ〉 of an ensemble of randomly oriented molecules were obtained by comparing the conjugate signal from a solution of the molecules with the signal from a reference liquid (THF). The estimated effective values of χ⁽³⁾, the third-order optical susceptibility, of cumulenic compounds with extended conjugation of the π-electron system are high, partly due to the strong nonlinear optical response of the molecules in their ground state and partly due to the resonance enhancement at the operating wavelength, 602 nm.