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Structural dynamics in proteins induced by and probed with X-ray free-electron laser pulses
摘要： X-ray free-electron lasers (XFELs) enable crystallographic structure determination beyond the limitations imposed upon synchrotron measurements by radiation damage. The need for very short XFEL pulses is relieved through gating of Bragg diffraction by loss of crystalline order as damage progresses, but not if ionization events are spatially non-uniform due to underlying elemental distributions, as in biological samples. Indeed, correlated movements of iron and sulfur ions were observed in XFEL-irradiated ferredoxin microcrystals using unusually long pulses of 80 fs. Here, we report a femtosecond time-resolved X-ray pump/X-ray probe experiment on protein nanocrystals. We observe changes in the protein backbone and aromatic residues as well as disulfide bridges. Simulations show that the latter’s correlated structural dynamics are much slower than expected for the predicted high atomic charge states due to significant impact of ion caging and plasma electron screening. This indicates that dense-environment effects can strongly affect local radiation damage-induced structural dynamics.
关键词： plasma electron screening,radiation damage,ion caging,structural dynamics,protein nanocrystals,X-ray free-electron lasers
更新于2025-09-23 15:21:01
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Double-pulse speckle contrast correlations with near Fourier transform limited free-electron laser light using hard X-ray split-and-delay
摘要： the ability to deliver two coherent X-ray pulses with precise time-delays ranging from a few femtoseconds to nanoseconds enables critical capabilities of probing ultra-fast phenomena in condensed matter systems at X-ray free electron laser (feL) sources. Recent progress made in the hard X-ray split-and-delay optics developments now brings a very promising prospect for resolving atomic-scale motions that were not accessible by previous time-resolved techniques. Here, we report on characterizing the spatial and temporal coherence properties of the hard X-ray feL beam after propagating through split-and-delay optics. Speckle contrast analysis of small-angle scattering measurements from nanoparticles reveals well-preserved transverse coherence of the beam. Measuring intensity fluctuations from successive X-ray pulses also reveals that only single or double temporal modes remain in the transmitted beam, corresponding to nearly fourier transform limited pulses.
关键词： spatial coherence,split-and-delay optics,speckle contrast,temporal coherence,X-ray Free Electron Lasers
更新于2025-09-23 15:19:57
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Improved molecular structure retrieval method for photoelectron holography
摘要： Photoelectron holography is a method that retrieves molecular structure information from photoelectron diffraction patterns generated by x-ray free-electron lasers, which have the promise of following dynamic molecular structure evolutions with angstrom spatial and femtosecond temporal resolutions (the so-called molecular movie). However, an additional phase is introduced when the photoelectron is scattered by an atom, and this scattering phase turns into a spatial error when the position of the atom is retrieved using a Fourier-type transform. We propose a method to remove, or greatly suppress, this error, with demonstrations using numerical examples.
关键词： x-ray free-electron lasers,Fourier-type transform,molecular structure retrieval,scattering phase,photoelectron holography
更新于2025-09-12 10:27:22
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Generation and Characterization of Intense Ultralow-Emittance Electron Beams for Compact X-Ray Free-Electron Lasers
摘要： The transverse emittance of the electron beam is a fundamental parameter in linac-based x-ray free-electron lasers (FELs). We present results of emittance measurements carried out at SwissFEL, a compact x-ray FEL facility at the Paul Scherrer Institute in Switzerland, including a description of the novel high-resolution measurement techniques and the optimization procedure. We obtained slice emittance values at the undulator entrance down to 200 nm for an electron beam with a charge of 200 pC and an rms duration of 30–40 fs. Furthermore, we achieved slice emittances as low as 100 nm for 10 pC beams with few fs duration. These values set new standards for electron linear accelerators. The quality, verification, and control of our electron beams allowed us to generate high-power FEL radiation for a wavelength as short as 0.1 nm using an electron beam with an energy of only 6 GeV. The emittance values demonstrated at SwissFEL would allow producing hard x-ray FEL pulses with even lower-energy beams, thus paving the way for even more compact and cost-effective FEL facilities.
关键词： x-ray free-electron lasers,emittance,SwissFEL,electron beams
更新于2025-09-11 14:15:04
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Microbunch Rotation and Coherent Undulator Radiation from a Kicked Electron Beam
摘要： Coherent emission from a microbunched electron beam is the driving force behind the revolution in light sources, enabling x-ray free-electron lasers (FELs) to emit pulses 9 orders of magnitude brighter than previous sources. Microbunches form perpendicular to the electron travel direction, and the conventional understanding is that they shear rather than rotate in response to a transverse kick, locking FEL facilities into a single-user operating mode. In this paper, we show that microbunches rotate toward the new direction of travel if the electron beam is kicked and defocused. We provide evidence that microbunch rotation explains the unexpectedly large amount of off-axis radiation observed during experiments at the Linac Coherent Light Source. We demonstrate that LCLS can be multiplexed into at least three separate beams using this principle. Finally, we propose using a magnetic triplet to rotate microbunches through significantly larger angles without microbunch degradation. This new understanding of microbunch dynamics can lead to significantly improved multiplexing at FEL facilities, microbunch preservation through a bend, and x-ray pulses with a pulse-front tilt.
关键词： electron beam,Linac Coherent Light Source,coherent undulator radiation,x-ray free-electron lasers,microbunch rotation
更新于2025-09-09 09:28:46