Breaking 50 Femtosecond Resolution Barrier in MeV Ultrafast Electron Diffraction with a Double Bend Achromat Compressor

Qi, Fengfeng; Ma, Zhuoran; Zhao, Lingrong; Cheng, Yun; Jiang, Wenxiang; Lu, Cewu; Jiang, Tao; Qian, Dong; Wang, Zhe; Zhang, Wentao; Zhu, Ping; Zou, Xu; Wan, Weishi; Xiang, Dao; Zhang, Jie

doi:10.1103/physrevlett.124.134803

Cited by 87 publications

(52 citation statements)

References 30 publications

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“… To minimize the timing jitter due to different beam energy, the quantity R 56 , which is defined as where , is designed to match the energy chirp of the incoming electron beam 26 . Based on the work of Qi et al, instead of constructing a double bend achromat with three quadrupoles 30 , reverse bending magnets are placed in the monochromator to adjust the energy-dependent path length difference ( R 56 ) such that the overall energy-dependent path length difference between cathode and sample is minimized achieving the bunch compression. Due to the space-charge effect, electrons in the bunch tail have lower energies than electrons in the head; they go through shorter pathlengths in the monochromator catching up with electrons in the head.…”

Section: Resultsmentioning

confidence: 99%

“…The result provides a major step forward, towards the UEM with a sub-nm resolution and the time resolved UED with an angular resolution comparable to XFEL (≤ 10 −3 ). A MeV electron beam with a femtosecond bunch length has been demonstrated experimentally 30 . Thanks to the reverse-bend achromat design of the monochromator, the energy-dependent timing jitter can be greatly reduced with no need of quadrupoles.…”

Section: Discussionmentioning

confidence: 99%

“…Six electromagnetic dipoles (four 60° bends and two − 30° reverse bends) provide the required dispersion of 0.645 m. The edge angles of the 60-degree bending magnets are adjusted such that an achromatic condition is achieved at the exit of the monochromator and that the monochromator is a round lens. The overall energy-dependent path length difference between the cathode and the sample is minimized 30 . The length of the electron bunches and the energy-dependent timing jitter can be greatly reduced down to the 10 fs level.…”

Section: Methodsmentioning

confidence: 99%

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Toward monochromated sub-nanometer UEM and femtosecond UED

Yang

Wan

Smaluk

et al. 2020

Sci Rep

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A preliminary design of a mega-electron-volt (MeV) monochromator with 10−5 energy spread for ultrafast electron diffraction (UED) and ultrafast electron microscopy (UEM) is presented. Such a narrow energy spread is advantageous in both the single shot mode, where the momentum resolution in diffraction is improved, and the accumulation mode, where shot-to-shot energy jitter is reduced. In the single-shot mode, we numerically optimized the monochromator efficiency up to 13% achieving 1.3 million electrons per pulse. In the accumulation mode, to mitigate the efficiency degradation caused by the shot-to-shot energy jitter, an optimized gun phase yields only a mild reduction of the single-shot efficiency, therefore the number of accumulated electrons nearly proportional to the repetition rate. Inspired by the recent work of Qi et al. (Phys Rev Lett 124:134803, 2020), a novel concept of applying reverse bending magnets to adjust the energy-dependent path length difference has been successfully realized in designing a MeV monochromator to achieve the minimum energy-dependent path length difference between cathode and sample. Thanks to the achromat design, the pulse length of the electron bunches and the energy-dependent timing jitter can be greatly reduced to the 10 fs level. The introduction of such a monochromator provides a major step forward, towards constructing a UEM with sub-nm resolution and a UED with ten-femtosecond temporal resolution. The one-to-one mapping between the electron beam parameter and the diffraction peak broadening enables a real-time nondestructive diagnosis of the beam energy spread and divergence. The tunable electric–magnetic monochromator allows the scanning of the electron beam energy with a 10−5 precision, enabling online energy matching for the UEM, on-momentum flux maximizing for the UED and real-time energy measuring for energy-loss spectroscopy. A combination of the monochromator and a downstream chicane enables “two-color” double pulses with femtosecond duration and the tunable delay in the range of 10 to 160 fs, which can potentially provide an unprecedented femtosecond time resolution for time resolved UED.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Toward monochromated sub-nanometer UEM and femtosecond UED

Yang

Wan

Smaluk

et al. 2020

Sci Rep

Self Cite

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“…Therefore, with UED it is possible to retrieve dynamical structural information directly from the experimental data without theoretical modeling of the effect of the probe on the system. Significant effort has been devoted recently to improve the temporal resolution of UED experiments, mostly transitioning from tabletop keV setups [10][11][12] to relativistic mega-electron-volt (MeV) instruments [13][14][15][16]. However, these instruments have not significantly increased the average electron beam current, which has become a limiting factor in gas-phase UED.…”

Section: Introductionmentioning

confidence: 99%

High-resolution movies of molecular rotational dynamics captured with ultrafast electron diffraction

Xiong

Wilkin

Centurion

2020

Phys. Rev. Research

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Imaging the structure of molecules during a photoinduced reaction is essential for elucidating reaction mechanisms. This requires high spatiotemporal resolution to capture nuclear motions on the femtosecond and subangstrom scale, and a sufficiently high signal level to sample their continuous evolution with high fidelity. Here we show that, using high-repetition-rate ultrafast electron diffraction, we can accurately reconstruct a movie of the coherent rotational motion of laser-aligned nitrogen molecules. We have used a tabletop 90-keV photoelectron gun to simultaneously achieve high temporal resolution of 240 fs full width at half maximum and an electron beam current that is more than an order of magnitude above the previous state of the art in gas-phase ultrafast electron diffraction. With this, we have made an essentially continuous real-space experimental movie of the rotational motion of the molecular wave packet as it evolves from initial alignment and past multiple revivals.

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“…In particular, any laser or plasma wakefield generated beam would benefit from the deployment of the following proposed schemes for transport and conditioning. Additionally, the schemes hereby proposed are particularly suited to adoption in the rapidly developing field of electron diffraction facilities [11,12].…”

Section: Introductionmentioning

confidence: 99%

Arclike variable bunch compressors

Williams

Segurana

Bailey

et al. 2020

Phys. Rev. Accel. Beams

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Electron bunch compressors formed of achromat arcs have a natural advantage over the more commonly used chicane compressors in that linearization of the longitudinal phase space is of the correct sign to compensate for the curvature imprinted by rf acceleration. Here we extend the utility of arc compressors to enable variation of the longitudinal compaction within a fixed footprint. We also show that this variability can be achieved independently order by order in momentum deviation. The technique we employ consists of additional dipoles, leading to the advantageous property that variability can be achieved without incurring significant penalty in terms of chromatic degradation. We show this by comparison to an alternative system where additional quadrupoles are utilized to enable variation of momentum compaction. Each of these alternative approaches are being considered in the context of an upgrade of the MAX IV linac, Sweden, to enable a soft x-ray free-electron laser in addition to its existing functions.

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Breaking 50 Femtosecond Resolution Barrier in MeV Ultrafast Electron Diffraction with a Double Bend Achromat Compressor

Cited by 87 publications

References 30 publications

Toward monochromated sub-nanometer UEM and femtosecond UED

Toward monochromated sub-nanometer UEM and femtosecond UED

High-resolution movies of molecular rotational dynamics captured with ultrafast electron diffraction

Arclike variable bunch compressors

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