Electric Field Measurement of Femtosecond Time-Resolved Four-Wave Mixing Signals in Molecules

TL;DR

This paper demonstrates a method to measure femtosecond electric fields of nonlinear signals in molecules, revealing detailed ultrafast electronic and rotational dynamics through time-resolved four-wave mixing spectroscopy.

Contribution

It introduces a novel application of TADPOLE technique to measure electric fields in femtosecond nonlinear optical signals, providing new insights into molecular nonlinear responses.

Findings

Electronic and rotational contributions to nonlinear response are distinguishable by their chirp signatures.

The electronic contribution exhibits a higher and time-dependent chirp compared to rotational effects.

Electric field-resolved spectroscopy reveals detailed ultrafast molecular dynamics.

Abstract

We report an experiment to measure the femtosecond electric field of the signal emitted from an optical third-order nonlinear interaction in carbon dioxide molecules. Using degenerate four-wave mixing with femtosecond near infrared laser pulses in combination with the ultra-weak femtosecond pulse measurement technique of TADPOLE, we measure the nonlinear signal electric field in the time domain at different time delays between the interacting pulses. The chirp extracted from the temporal phase of the emitted nonlinear signal is found to sensitively depend on the electronic and rotational contributions to the nonlinear response. While the rotational contribution results in a nonlinear signal chirp close to the chirp of the input pulses, the electronic contribution results in a significantly higher chirp which changes with time delay. Our work demonstrates that electric field-resolved nonlinear spectroscopy offers detailed information on nonlinear interactions at ultrafast time scales.