Ultrafast pulses of X-ray lasers reveal how atoms are moving on femtosecond time scales. That’s a millionth of a second. However, measuring the properties of the pulses themselves is challenging. While determining the maximum pulse strength, or “amplitude”, it is direct, and often the time when the pulse reaches its maximum, or “phase” is hidden. A new study trains neural networks to analyze impulses to reveal these hidden subcomponents. Physicists also call these subcomponents “real” and “imaginary.” Starting with low-resolution measurements, neural networks reveal finer details with each pulse, and can analyze pulses millions of times faster than previous methods.
The new analysis method is up to three times more accurate and millions of times faster than existing methods. Knowing the components of each X-ray pulse leads to better and clearer data. This will expand the range of science possible with ultrafast X-ray lasers, including basic research in chemistry, physics and materials science, and applications in areas such as quantum computing. For example, the additional pulse information could enable simpler and higher-resolution experiments of time-resolution, reveal new areas in physics, and open the door to new investigations in quantum mechanics. The neural network approach used here could have wide applications in x-ray and accelerator science, including learning the shape of proteins or electron beam properties.
Characterizations of system dynamics are important applications of X-ray free electron lasers (XFELs), but measuring the time-domain properties of the X-ray pulses used in those experiments is a long-standing challenge. Diagnosing the characteristics of each individual XFEL pulse could enable a new class of simpler and possibly higher-resolution dynamics experiments. This research, conducted by scientists from SLAC National Accelerator Laboratory and Deutsches Elektronen-Synchrotron, is a step toward that goal. The new approach trains neural networks, a form of machine learning, to combine low-resolution measurements in both the time and frequency domains and restore the properties of X-ray pulses with high accuracy. This ‘physics-informed’ model-based neural network architecture can be trained directly on unlabeled experimental data and is fast enough for real-time analysis on new generation Megahertz XFELs. Crucially, the method also recovers the phase, opening the door to coherent control experiments with XFELs, shaping the complex motion of electrons in molecules and condensed matter systems.
The search was published in Optix Express.
Machine learning paves the way for smarter particle accelerators
Rattner et al., Phase and amplitude recovery of FEL X-ray pulses using neural networks and differentiable models, Optix Express (2021). doi: 10.1364/OE.432488
Provided by the US Department of Energy
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