High-Power Polarization-Controlled Attosecond-Scale Soft X-ray Pulses

Zhaoheng Guo; Carlo Vicario; Andre Al Haddad; Christopher Arrell; Andreas Dax; Umit Demirbas; Nicole Hiller; Martin Huppert; Christoph Kittel; Gregor Knopp; Eduard Prat; Sven Reiche; Antoine Sarracini; Thomas Schietinger; Kirsten Schnorr; Alexandre Trisorio; Didier Voulot; Tobias Weilbach; Hankai Zhang; Christoph Bostedt; Philipp Dijkstal

arXiv · 2606.31335

High-Power Polarization-Controlled Attosecond-Scale Soft X-ray Pulses

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Abstract

We demonstrate a versatile platform for high-power attosecond soft X-ray pulse generation with polarization and photon energy control at the SwissFEL free-electron laser. An isolated high-current spike embedded within a long electron-beam pedestal emits soft X-ray pulses with single-spike spectra and multi-electronvolt bandwidths in the tunable magnetic fields of Apple-X undulators. Demonstrated pulse parameters include a photon energy range of 450--1070 eV, circular as well as linear polarization, and pulse energies from tens to above hundred microjoules. By tuning the longitudinal slice-dependent transverse electron beam orbit we can rapidly switch between attosecond and few femtosecond pulse length. By exploiting magnetic chicanes in the undulator line we can produce two-colour pulse pairs with tunable delay or increase the pulse energy beyond 200~\textmu J through multi-stage amplification schemes. High-resolution longitudinal phase-space measurements and start-to-end simulations in addition to spectral measurements provide consistent evidence for attosecond-scale pulse durations. This unique combination of high pulse energy and polarization control of attosecond-scale soft X-ray pulses enables the element-specific investigations of spin and chiral dynamics on the natural time scale of electron motion.

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Zhaoheng Guo, Carlo Vicario, Andre Al Haddad, Christopher Arrell, Andreas Dax, Umit Demirbas, Nicole Hiller, Martin Huppert, Christoph Kittel, Gregor Knopp, Eduard Prat, Sven Reiche, Antoine Sarracini, Thomas Schietinger, Kirsten Schnorr, Alexandre Trisorio, Didier Voulot, Tobias Weilbach, Hankai Zhang, Christoph Bostedt, Philipp Dijkstal. 2026-06-30. High-Power Polarization-Controlled Attosecond-Scale Soft X-ray Pulses. https://arxiv.org/abs/2606.31335

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