Physicists using SLAC's X-ray free-electron laser discovered two new laser phenomena that allowed them to generate the [1]shortest, highest-energy X-ray pulses ever recorded (60-100 attoseconds). These breakthroughs could let scientists observe electron motion and chemical bond formation in real time. Physicists Uwe Bergmann and Thomas Linker write in an article for The Conversation:

> In this new study we used X-rays, which have 100 million times shorter wavelengths than microwaves and 100 million times more energy. This meant the resulting new X-ray laser pulses were split into different X-ray wavelengths corresponding to [2]Rabi frequencies in the extreme ultraviolet region. Ultraviolet light has a frequency 100 million times higher than radio waves. This Rabi cycling effect allowed us to generate the shortest high-energy X-ray pulses to date, clocking in at 60-100 attoseconds.

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> While the pulses that X-ray free-electron lasers currently generate allow researchers to observe atomic bonds forming, rearranging and breaking, they are not fast enough to look inside the electron cloud that generates such bonds. Using these new attosecond X-ray laser pulses could allow scientists to study the fastest processes in materials at the atomic-length scale and to discern different elements.

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> In the future, we also hope to use much shorter X-ray free-electron laser pulses to better generate these attosecond X-ray pulses. We are even hoping to generate pulses below 60 attoseconds by using heavier materials with shorter lifespans, such as tungsten or hafnium. These new X-ray pulses are fast enough to eventually enable scientists to answer questions such as how exactly an electron cloud moves around and what a chemical bond actually is.

The findings have been [3]published in the journal Nature .



[1] https://theconversation.com/our-team-of-physicists-inadvertently-generated-the-shortest-x-ray-pulses-ever-observed-258776

[2] https://en.wikipedia.org/wiki/Rabi_frequency

[3] https://doi.org/10.1038/s41586-025-09105-9