X-ray Coherent Attosecond Pulse Pair Spectroscopy

Zain Abhari; Thomas M. Linker; Thomas Kroll; Yurina Michine; Gota Yamaguchi; Yuichi Inubushi; Taito Osaka; Jumpei Yamada; Ichiro Inoue; Makina Yabashi; Aliaksei Halavanau; Andrei Benediktovitch; Nina Rohringer; Matthias F. Kling; Claudio Pelligrini; Hitoki Yoneda; Uwe Bergmann

arXiv · 2607.00285

X-ray Coherent Attosecond Pulse Pair Spectroscopy

Zain Abhari·Thomas M. Linker·Thomas Kroll·Yurina Michine·Gota Yamaguchi·Yuichi Inubushi·Taito Osaka·Jumpei Yamada·Ichiro Inoue·Makina Yabashi·Aliaksei Halavanau·Andrei Benediktovitch·Nina Rohringer·Matthias F. Kling·Claudio Pelligrini·Hitoki Yoneda·Uwe Bergmann

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Abstract

X-ray free electron laser (XFEL) experiments using self-amplified spontaneous emission (SASE) pulses typically achieve temporal resolutions of order several femtoseconds, as the pulse duration puts a practical limit to pump-probe or probe-probe schemes. Even with the emerging capabilities to generate pulses with attosecond durations with new single-spike SASE schemes, direct access to attosecond electron dynamics remains an experimental challenge. Here we show how X-ray coherent attosecond pulse-pair spectroscopy (X-CAPPS) provides a powerful new approach to access the ultrashort time-delay window. Coherent attosecond pulse pairs with time delays varying from ~500 as to ~5 fs are generated with Cu K$\alpha_1$ stimulated X-ray emission from a gain medium pumped by intense SASE XFEL pulses. These pulse pairs are analyzed with two subsequent Bragg crystal spectrometers, and the resulting interference spectrum is captured on two sequential 2D image detectors encoding their time separation, relative amplitudes, and phases with high precision. X-CAPPS requires no split-and-delay X-ray optics, nor XFEL pulse modifications, making it broadly implementable across existing facilities. This technique enables the investigation of attosecond processes with $\mathring{A}$ngstr\"{o}m resolution, providing a new tool for probing ultrafast dynamics across a wide range of atomic, molecular, and solid systems.

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Zain Abhari, Thomas M. Linker, Thomas Kroll, Yurina Michine, Gota Yamaguchi, Yuichi Inubushi, Taito Osaka, Jumpei Yamada, Ichiro Inoue, Makina Yabashi, Aliaksei Halavanau, Andrei Benediktovitch, Nina Rohringer, Matthias F. Kling, Claudio Pelligrini, Hitoki Yoneda, Uwe Bergmann. 2026-07-01. X-ray Coherent Attosecond Pulse Pair Spectroscopy. https://arxiv.org/abs/2607.00285

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