Multiple Core-Hole Coherence in X-Ray Four-Wave-Mixing Spectroscopies

TL;DR

This paper derives correlation-function expressions for the coherent nonlinear response of molecules to ultrafast x-ray pulses, enabling controlled creation of two-core-hole states to probe valence electron dynamics with potential new insights.

Contribution

It introduces a theoretical framework for four-wave-mixing in the x-ray regime, allowing controlled core-hole state creation and analysis of valence electron response.

Findings

Derived closed-form correlation functions for the electron-boson model.

Showed potential to test and refine electronic excitation models.

Enabled new multidimensional nonlinear spectroscopy techniques.

Abstract

Correlation-function expressions are derived for the coherent nonlinear response of molecules to three resonant ultrafast pulses in the x-ray regime. The ability to create two-core-hole states with controlled attosecond timing in four-wave-mixing and pump probe techniques should open up new windows into the response of valence electrons, which are not available from incoherent x-ray Raman and fluorescence techniques. Closed expressions for the necessary four-point correlation functions are derived for the electron-boson model by using the second order cumulant expansion to describe the fluctuating potentials. The information obtained from multidimensional nonlinear techniques could be used to test and refine this model, and establish an anharmonic oscillator picture for electronic excitations.