Time-Resolved Measurement of Ultrafast, Weak Electric Fields Signals in Degenerate Four-Wave Mixing Schemes

Nonlinear optical spectroscopic techniques are ubiquitous tools in the study of ultrafast electron dynamics in molecules. By combining well-known four-wave mixing schemes such as Degenerate Four-Wave Mixing (DFWM) and spectral interferometry, ultraweak, ultrafast signals carrying information on ultrafast dynamics can be measured. We demonstrate that with DWFM in a conventional BoxCARS configuration, spectral interferometry can be used to measure nonlinear signal electric fields with attosecond time delay resolution between input pulses. We further use this approach to measure electric field of nonlinear signals from molecules such as ethylene excited to electronic states using femtosecond ultraviolet pulses.