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Exploring ultra-small and ultra-fast objects through advances in attosecond science

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In two recent experiments, SLAC researchers demonstrated new ways to use attosecond pulses in pump probe experiments and generate high-energy attosecond X-ray pulses. Credit: Greg Stewart/SLAC National Accelerator Laboratory

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In two recent experiments, SLAC researchers demonstrated new ways to use attosecond pulses in pump probe experiments and generate high-energy attosecond X-ray pulses. Credit: Greg Stewart/SLAC National Accelerator Laboratory

A team of scientists at the Department of Energy’s SLAC National Accelerator Laboratory is developing new ways to explore the finer details of the universe at extraordinary speeds.

In previous research, researchers developed a method to produce X-ray laser bursts several hundred totoseconds (or billionths of a second) long. This method, called X-ray laser-enhanced attosecond pulse generation (XLEAP), allows scientists to investigate how electrons orbiting molecules catalyze key processes in biology, chemistry, materials science and more.

Now, led by SLAC scientists Agostino Marinelli and James Cryan, the team has developed new tools to use these attosecond pulses in pioneering ways: the first use of attosecond pulses in pump probe experiments and the production of the most powerful attosecond X-ray pulses ever reported. The experiments were performed using SLAC’s Linac Coherent Light Source (LCLS) free-form X-ray laser and published in two Stuff in Nature photonicsIt could revolutionize fields ranging from chemistry to materials science by providing insight into the fastest movements within atoms and molecules.

A new way to measure ultrafast phenomena

In the first development, the researchers presented a new approach to performing “pump-probe” experiments using attosecond X-ray pulses. These experiments aim to measure ultrafast events of less than a trillionth of a second, and involve exciting atoms with a “pump” pulse and then probing them with a second pulse to observe the resulting changes.

This technology allowed scientists to track and measure electron movement within atoms and molecules, a crucial process that affects chemical reactions, material properties, and biological functions. They accomplished this by generating pairs of laser pulses in two colors and precisely controlling the delay between them to at least 270 attoseconds.

“This ability opens new opportunities to study the interaction of light with matter at a fundamental level,” Cryan said. “It’s exciting because it has evolved into a practical tool, enabling us to see electron dynamics that were previously beyond our reach. We are now observing processes that occur on timescales approaching the time it takes light to pass through a molecule.”

In a recent paper, researchers used this technique to observe electrons moving in real time in liquid water. Future studies will apply this method to different molecular systems, improving the accuracy of these measurements and expanding their application across scientific disciplines.

Create high-energy totosecond pulses

The second development focused on generating high-energy attosecond pulses using a technique known as “super radiation,” achieving power levels approaching one terawatt. This process involved cascading the impact of a zero-electron X-ray laser, which greatly amplified the strength of the pulses.

The increased intensity of these pulses allows scientists to explore unique states of matter and watch phenomena that occur on shorter timescales.

“These are the most powerful attosecond X-ray pulses ever reported,” Marinelli said. “We have gone beyond the energy limits of the X-ray pulse, reaching energy levels that open up new experimental worlds. This result was achieved thanks to a special type of wave that maintains its shape and speed as it propagates through the electron beam, dramatically enhancing the intensity and energy of our pulses.”

The researchers plan to continue improving this technology to enhance stability and control of these high-energy pulses, with the aim of expanding its application in various scientific fields.

Advance scientific exploration

These advances push the limits of our observational and measurement capabilities, paving the way for future scientific discoveries that could change our understanding of the natural world.

Observing atoms and electrons in motion makes it easier to design new materials with tailored properties for technology, energy and other fields. Understanding electron movement during chemical reactions can also facilitate principles of intelligent chemical design.

“These studies not only deepen our understanding of physics, but also pave the way for future innovations that could change our understanding of electron-dependent processes,” Cryan said. “Every totosecond pulse we generate offers a new glimpse into nature’s building blocks, revealing dynamics previously hidden from view. We expect many exciting discoveries in the future.”

more information:
Zhaoheng Guo et al., Experimental demonstration of attosecond pump spectroscopy using a free-electron X-ray laser, Nature photonics (2024). doi: 10.1038/s41566-024-01419-s

Paris Franz et al., Totosecond-terawatt-scale X-ray pulses from a cascaded ultra-radiant free-electron laser, Nature photonics (2024). doi: 10.1038/s41566-024-01427-s

Log information:
Nature photonics

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