Search

X-ray free-electron lasers (XFELs) as the world's brightest light sources provide ultrashort X-ray pulses with a duration typically in the order of femtoseconds. Recently, they have approached and entered the attosecond regime, which holds new promises for single-molecule imaging and studying nonlinear and ultrafast phenomena such as localized electron dynamics. The technological evolution of XFELs toward well-controllable light sources for precise metrology of ultrafast processes has been, however, hampered by the diagnostic capabilities for characterizing X-ray pulses at the attosecond frontier. In this regard, the spectroscopic technique of photoelectron angular streaking has successfully proven how to non-destructively retrieve the exact time--energy structure of XFEL pulses on a single-shot basis. By using artificial intelligence techniques, in particular convolutional neural networks, we here show how this technique can be leveraged from its proof-of-principle stage toward routine diagnostics even at high-repetition-rate XFELs, thus enhancing and refining their scientific accessibility in all related disciplines.

Physik in unserer Zeit 53(5), 220 - 228 (2022). doi:10.1002/piuz.202201643, Der Auger-Effekt ist ein fundamentaler Prozess, bei dem Energie in Materie, etwa nach Aufnahme kurzwelliger Strahlung, durch Abgabe von Elektronen typischerweise innerhalb weniger Femtosekunden umverteilt wird. Experimente an Röntgenlasern machen es nun möglich, diesen bedeutsamen Effekt in bisher unerforschten Zuständen der Materie und in „Echtzeit“ zu untersuchen. Hierdurch lässt sich die interdisziplinäre Bedeutung des Auger-Prozesses aus ganz neuen Blickwinkeln studieren, und wir erlangen im Detail Zugang zur ultraschnellen Dynamik der komplexen elektronischen Struktur von Materie., Published by Wiley-VCH, Weinheim

Scientific reports 11(1), 3562 (2021). doi:10.1038/s41598-021-82597-3, We present a novel, highly versatile, and self-referenced arrival time monitor for measuring the femtosecond time delay between a hard X-ray pulse from a free-electron laser and an optical laser pulse, measured directly on the same sample used for pump-probe experiments. Two chirped and picosecond long optical supercontinuum pulses traverse the sample with a mutually fixed time delay of 970 fs, while a femtosecond X-ray pulse arrives at an instant in between both pulses. Behind the sample the supercontinuum pulses are temporally overlapped to yield near-perfect destructive interference in the absence of the X-ray pulse. Stimulation of the sample with an X-ray pulse delivers non-zero contributions at certain optical wavelengths, which serve as a measure of the relative arrival time of the X-ray pulse with an accuracy of better than 25 fs. We find an excellent agreement of our monitor with the existing timing diagnostics at the SACLA XFEL with a Pearson correlation value of 0.98. We demonstrate a high sensitivity to measure X-ray pulses with pulse energies as low as 30 μJ. Using a free-flowing liquid jet as interaction sample ensures the full replacement of the sample volume for each X-ray/optical event, thus enabling its utility even at MHz repetition rate XFEL sources., Published by Macmillan Publishers Limited, part of Springer Nature, [London]