Electrons determine everything: how chemical reactions unfold, how materials conduct electricity, how biological molecules transfer energy, and how quantum technologies operate. But electron dynamics happens on attosecond timescales—far too fast for conventional measurement tools.

Researchers have now generated a 19.2-attosecond soft X-ray pulse, which effectively creates a camera capable of capturing these elusive dynamics in real time with unprecedented detail, enabling the observation of processes never observed before. Dr. Fernando Ardana-Lamas, Dr. Seth L. Cousin, Juliette Lignieres, and ICREA Prof. Jens Biegert, at ICFO, have published this new record in Ultrafast Science. At just 19.2 attoseconds long, it is the shortest and brightest soft X-ray pulse ever produced, giving rise to the fastest ‘camera’ in existence.

Flashes of light in the soft X-ray spectral range provide fingerprinting identification, allowing scientists to track how electrons reorganize around specific atoms during reactions or phase transitions. Generating an isolated pulse this short, required innovations in high-harmonic generation, advanced laser engineering, and attosecond metrology. Together, these developments allow researchers to observe electron dynamics, which define material properties, at their natural timescales.

The journey towards this milestone, however, began in 2015, when Prof. Jens Biegert’s team pioneered the generation of attosecond pulses in the soft X-ray regime by successfully isolating attosecond bursts of this light. These pulses demonstrated their breakthrough utility by resolving the interaction of electrons with the crystal lattice in a solid and by elucidating how and when a molecular ring opens as a precursor to processes such as polymerization. But, at that time, the method for pinpointing the duration had limitations that could now be overcome, leading to the demonstration of the shortest pulse ever measured.

“When I came to the group and saw the striking traces, I had to look into this with a new pulse retrieval method,” shares enthusiastically the first author, Dr. Fernando Ardana-Lamas. “Finally, we can say that, to the best of our knowledge, we have confirmed the shortest pulse of light in the world!”

“This new capability paves the way for breakthroughs in physics, chemistry, biology, and quantum science, enabling direct observation of processes that drive photovoltaics, catalysis, correlated materials, and emerging quantum devices” explains Prof. Biegert, reflecting on the future of attosecond soft X-ray pulses below the atomic unit of time. As he puts it, now that the foundations are laid, “the sky is the limit.”

References:

[1] Fernando Ardana-Lamas, Seth L. Cousin, Juliette Ligneres, Jens Biegert. Brilliant source of 19.2 attosecond soft X-ray pulses below the atomic unit of time. Ultrafast Sci. 0:

DOI: 10.34133/ultrafastscience.0128

Acknowledgements:

J.B. and group acknowledges financial support from the European Research Council forERC Advanced Grant “TRANSFORMER” (788218), ERC Proof of Concept Grant “miniX”(840010), FET-OPEN “PETACom” (829153), FET-OPEN “OPTOlogic” (899794), FET-OPEN“TwistedNano” (101046424), MINECO for Plan Nacional PID2024-162757NB-I00; QU-ATTO,101168628; AGAUR for 2021 SGR 01449, MINECO for “Severo Ochoa” (CEX2019-000910-S),Fundació Cellex Barcelona, the CERCA Programme/Generalitat de Catalunya, and the Alexander von Humboldt Foundation for the Friedrich Wilhelm Bessel Prize. JB also acknowledges Lasers4EU, which is funded by the European Union funds under HEU-GA 101131771.