Relaxation time measurement: correlating diffraction patterns

Dynamics in liquids and glasses can be assessed using X-ray photon correlation spectroscopy or electron correlation microscopy, which involves measuring the temporal changes in diffraction patterns. Two methods are commonly used to evaluate these temporal changes: one-time correlation function or two-time correlation function. However, the specific characteristics of these methods have not been thoroughly studied. In this study, we investigated the differences between these methods and found that the two-time correlation function can measure dynamics for longer periods than the method relying on the one-time correlation function. Additionally, we demonstrated that the two-time correlation function exhibits a weak dependence on the amount of dose applied.