Time-resolved broadband Raman spectroscopies; A unified six-wave-mixing representation

TL;DR

This paper unifies various time-resolved broadband Raman spectroscopic techniques under a six-wave-mixing framework, clarifying their common molecular correlation functions and providing simulations to explain experimental features.

Contribution

It establishes a unified six-wave-mixing representation for different Raman spectroscopic methods, linking their signals through common molecular correlation functions.

Findings

All signals can be described as six-wave-mixing processes.

Simulations illustrate the origin of absorptive and dispersive features.

The framework connects spontaneous and stimulated Raman detection methods.

Abstract

Excited-state vibrational dynamics in molecules can be studied by an electronically off-resonant Raman process induced by a probe pulse with variable delay with respect to an actinic pulse. We establish the connection between several variants of the technique that involve either spontaneous or stimulated Raman detection and different pulse configurations. By using loop diagrams in the frequency domain we show that all signals can be described as six wave mixing which depend on the same four point molecular correlation functions involving two transition dipoles and two polarizabilities and accompanied by a different gating. Simulations for the stochastic two-state-jump model illustrate the origin of the absorptive and dispersive features observed experimentally.