Direct Electric Field Reconstruction of Femtosecond Time-Resolved Four-Wave Mixing Signals

We describe a method to measure the real and imaginary parts of the third order non-linear response in molecules and materials by directly measuring the electric field of four-wave mixing signals. We use the four-wave mixing process of Optical Kerr-effect (OKE) to measure the nonlinear response and use the TADPOLE (Temporal Analysis by Dispersing a Pair of Light E Fields) technique to reconstruct the electric field of the weak four-wave mixing signal. Typically, the real and imaginary parts of the third-order nonlinear response are measured in a heterodyne scheme using a local oscillator as a reference field. Such measurements, especially when adopted in ultrafast time-resolved experiments, can be cumbersome. Our method of direct electric field reconstruction of the nonlinear signal makes these measurements much simpler without requiring a heterodyne scheme. We demonstrate this method by reconstructing the electric field of OKE signals in carbon dioxide gas and fused silica glass. These studies are an important step towards complete measurement of the third-order non-linear response for probing ultrafast dynamics in molecules and materials.