Advancing Two-Time Correlation Analysis for Non-Equilibrium XPCS Measurements

X-ray Photon Correlation Spectroscopy (XPCS) enables the study of dynamics across an exceptional range of spatial and temporal scales. Central to these experiments is the accurate determination and interpretation of the speckle correlation function. While significant progress has been made in computing the two-time correlation function, the subsequent analysis and physical interpretation of these correlations—particularly in non-equilibrium systems—remain challenging.

Here, we present a framework for analyzing and classifying two-time correlation data, emphasizing approaches suitable for non-equilibrium dynamics. Using both experimental datasets, including LSCO measurements from CHX (NSLS-II) and ID10 (ESRF), and simulated data, we demonstrate how different projections and one-time fits can reveal evolving dynamical behavior. Our approach also enables the identification of setup-dependent artifacts. Finally, we outline ongoing developments aimed at integrating AI/ML-based tools to automate and enhance non-equilibrium XPCS analysis.