One- and two-dimensional correlation spectroscopy analyses for resonant and non-resonant coherent nonlinear optical processes

TL;DR

This paper introduces one- and two-dimensional correlation spectroscopy methods to analyze complex resonant and non-resonant four wave mixing processes in coherent Raman scattering, enhancing understanding and visualization of these nonlinear optical phenomena.

Contribution

It presents novel correlation analysis tools, including diagonal projections, for better interpretation of resonant and non-resonant processes in coherent Raman spectroscopy.

Findings

Diagonal projections simplify 2D to 1D analysis

Analytical and experimental results demonstrate method effectiveness

Tools distinguish resonant from non-resonant processes

Abstract

Three-color coherent anti-Stokes Raman scattering represents non-degenerate four wave mixing process that includes both a non-resonant and resonant processes, the contributions of which depend on how the molecular vibrational modes are being excited by the input laser pulses. Non-degenerate four wave mixing processes are complex and understanding these processes requires rigorous data analytical tools, which still lack in this research field. In this work, we introduce one- and two-dimensional intensity-intensity correlation functions in terms of a new variable (e.g., probe pulse delay) and new perturbation parameter (e.g., probe pulse linewidth). In particular, diagonal projections are defined here as a tool to reduce both synchronous and asynchronous two-dimensional correlation spectroscopy analyses down to one-dimensional analysis, revealing valuable analytical information. Detailed analyses using the all Gaussian coherent Raman scattering closed-form solutions and the representative experimental data for resonant and non-resonant processes are presented and compared. This intensity-intensity correlation analytical tool holds a promising potential in resolving and visualizing resonant versus non-resonant four wave mixing processes for quantitative label-free species-specific nonlinear spectroscopy and microscopy.