Christopher Arrell

Subangstrom Free-Electron Laser Operation with Undulator Deflection Parameter Reaching the Subunity Regime

Anonymous, Christopher Arrell, Marco Calvi, Nicole Hiller et autres

X-ray free-electron lasers (XFELs) enable the exploration of matter with atomic-scale spatiotemporal resolution. Generating radiation wavelengths below one angstrom is critical for applications such as crystallography and Mössbauer studies. Until now, achieving the subangstrom regime has required electron beam energies ≥ 8 …

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Single-shot third-harmonic spectral diagnostics for tender X-ray FEL pulses using a bent-crystal spectrometer

Christopher Arrell, Henrik Till Lemke, Eduard Prat

The tender X-ray (2.0–4.0 keV) region provides access to the K -edges of light- and mid- Z elements that are central to catalysis, energy materials and soft condensed matter, but direct single-shot spectral diagnostics in this range are technically challenging. Ruled gratings …

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Ultrafast Decoherence of Charge Density Waves in K$_{0.3}$MoO$_{3}$

Rafael Winkler, Larissa Boie, Yunpei Deng, Matteo Savoini et autres

Recent works have suggested that transient suppression of a charge density wave (CDW) by an ultra-short excitation can lead to an inversion of the CDW phase. We experimentally investigate the dynamics of the CDW in K$_{0.3}$MoO$_{3}$ by time resolved x-ray diffraction after …

Ultrafast Decoherence of Charge Density Waves in K$_{0.3}$MoO$_{3}$

Rafael Winkler, Larissa Boie, Yunpei Deng, Matteo Savoini et autres

Recent works have suggested that transient suppression of a charge density wave (CDW) by an ultra-short excitation can lead to an inversion of the CDW phase. We experimentally investigate the dynamics of the CDW in K$_{0.3}$MoO$_{3}$ by time resolved x-ray diffraction after …

Enhancing hard X-ray beamline performance at SwissFEL through spontaneous radiation measurements

Christoph Kittel, M. Aiba, Christopher Arrell, Ariana Cassar et autres

The hard X-ray beamline (Aramis) of the Swiss free-electron laser (SwissFEL) has been in user operation since the end of 2017 and its performance has been continuously monitored and enhanced over the past eight years. From the beginning, spontaneous radiation has been …

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High magnification optical imaging systems for the characterization of soft X-ray focii

André Al Haddad, Antoine Sarracini, Kirsten Schnorr, Gregor Knopp et autres

We present a series of novel X-ray imaging systems designed specifically for the soft X-ray energy range, optimized for operation in ultra-high-vacuum environments and compactness. These systems achieve micrometre-level spatial resolution with high collection efficiency of visible light by using high numerical …

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Dynamical Scaling Reveals Topological Defects and Anomalous Evolution of a Photoinduced Phase Transition

Gal Orenstein, Ryan A. Duncan, Gilberto A. de la Peña Muñoz, Yijing Huang et autres

Nonequilibrium states of quantum materials can exhibit exotic properties and enable unprecedented functionality and applications. These transient states are inherently inhomogeneous, characterized by the formation of topologically protected structures, requiring nanometer spatial resolution on femtosecond timescales to resolve their evolution. Using ultrafast …

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Virtual photon diagnostics at SwissFEL for real-time spectral analysis

Christopher Arrell, Markus Schölmerich, Philipp Dijkstal, Sven Reiche

We present a method for real-time spectral analysis of SASE X-ray FEL spectra using a machine learning (ML) model. The model detects and counts SASE spikes, even when their widths fall below the spectrometer resolution. For a typical 20-30 fs SASE pulse …

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Experimental demonstration of mode-coupled and high-brightness SASE in an x-ray FEL

Eduard Prat, Wenxiang Hu, Christopher Arrell, Marco Calvi et autres

This contribution will present the first experimental demonstration of two schemes that enhance the longitudinal coherence of SASE X-ray FEL pulses: 1) mode-coupled SASE, which results in frequency combs with tunable peak separation; and 2) high-brightness SASE, producing FEL pulses with a …

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Commissioning results of the ATHOS-beamline at SwissFEL

R. Follath, Ulrich Wagner, Christopher Arrell, U. Flechsig

Abstract The Soft X-ray Free Electron Laser ATHOS at SwissFEL came into operation at the end of 2019 together with a variable line space grating monochromator. The beamline alternatively distributes the FEL-beam to two end stations namely Maloja and Furka. A third …

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Enhancing hard X-ray beamline performance atSwissFEL through spontaneous radiation measurements

Christoph Kittel, M. Aiba, Christopher Arrell, Ariana Cassar et autres

The hard X-ray beamline (Aramis) of the Swiss free-electron laser (SwissFEL) hasbeen in user operation since the end of 2017 and its performance has been continuouslymonitored and enhanced over the past eight years. From the beginning, spontaneousradiation has been utilized to monitor …

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Experimental Demonstration of Mode-Coupled and High-Brightness Self-Amplified Spontaneous Emission in an X-Ray Free-Electron Laser

Eduard Prat, Wenxiang Hu, Christopher Arrell, Marco Calvi et autres

X-ray free-electron lasers (FELs) are modern research tools with applications in multiple scientific fields. Standard x-ray FEL pulses are produced by the self-amplified spontaneous emission (SASE) mechanism. SASE-FEL pulses have high power, short duration, and excellent transverse coherence but exhibit poor temporal …

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