Determination of third-order optical nonlinearity of triphenylamine from femtosecond degenerate four-wave mixing in solutions

A positive real part and a sizeable imaginary part of the third-order nonlinear susceptibility X⁽³⁾(-ω;ωω-ω were determined in triphenylamine solutions in chloroform at an off-resonant wavelength of 800 nm with femtosecond pulses (FWHM 140 fs). The values and the sign of the components of the complex second hyperpolarizability on the order of γ-10^-35 esu were determined from analysis of a quadratic dependence of the degenerate four wave mixing (DFWM) signal on triphenylamine concentration, studied in the range 0 - 30 wt %. The analysis took into account changes of the linear refractive index and density of solutions with the solute concentration. The γ data were used to derive the nonlinear refractive index n₂, X⁽³⁾, and the two-photon absorption cross-section σ₂ of triphenylamine at 800 nm.