Abstract
One of the important challenges in condensed matter science is to understand ultrafast, atomic-scale fluctuations that dictate dynamic processes in equilibrium and non-equilibrium materials. Here, we report an important step towards reaching that goal by using a state-of-the-art perfect crystal based split-and-delay system, capable of splitting individual X-ray pulses and introducing femtosecond to nanosecond time delays. We show the results of an ultrafast hard X-ray photon correlation spectroscopy experiment at LCLS where split X-ray pulses were used to measure the dynamics of gold nanoparticles suspended in hexane. We show how reliable speckle contrast values can be extracted even from very low intensity free electron laser (FEL) speckle patterns by applying maximum likelihood fitting, thus demonstrating the potential of a split-and-delay approach for dynamics measurements at FEL sources. This will enable the characterization of equilibrium and, importantly also reversible non-equilibrium processes in atomically disordered materials.
Highlights
One of the important challenges in condensed matter science is to understand ultrafast, atomic-scale fluctuations that dictate dynamic processes in equilibrium and non-equilibrium materials
Time-domain XPCS18,19 at free electron laser (FEL) sources is well suited for studying fluctuations in reversible non-equilibrium processes that go beyond time-averaged structural descriptions
A region of interest from this pattern is shown in Fig. 2c highlighting the low probability that a given pixel will contain single, double or triple photon hits
Summary
One of the important challenges in condensed matter science is to understand ultrafast, atomic-scale fluctuations that dictate dynamic processes in equilibrium and non-equilibrium materials. This approach relies on diffractive optics[26,27,28,29] capable of splitting individual FEL pulses and introducing a tunable time delay Δt between the two subpulses that both diffract from the sample into a detector and produce a single speckle pattern.
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