Systematic understanding and real-time feedback capability for x-ray free electron laser (FEL) accelerator and optical components are critical for scientific experiments and instrument performance. ...Single-shot wavefront sensing enables characterization of the intensity and local electric field distribution at the sample plane, something that is important for understanding scientific experiments such as nonlinear studies. It can also provide feedback for alignment and tuning of the FEL beam and instrumentation optics, leading to optimal instrument performance and greater operational efficiency. A robust, sensitive, and accurate single-shot wavefront sensor for x-ray FEL beams using single grating Talbot interferometry has been developed. Experiments performed at the Linac Coherent Light Source (LCLS) demonstrate 3σ sensitivity and accuracy, both better than λ/100, retrieval of hard x-ray (λ = 0.13 nm, E = 9.5 keV) wavefronts in 3D. Exhibiting high performance from both unfocused and focused beams, the same setup can be used to systematically study the wavefront from the FEL output, beam transport optics, and endstation focusing optics. Finally, this technique can be extended for use with softer and harder x rays with modified grating configurations.
There is a fundamental interest in studying photoinduced dynamics in nanoparticles and nanostructures as it provides insight into their mechanical and thermal properties out of equilibrium and during ...phase transitions. Nanoparticles can display significantly different properties from the bulk, which is due to the interplay between their size, morphology, crystallinity, defect concentration, and surface properties. Particularly interesting scenarios arise when nanoparticles undergo phase transitions, such as melting induced by an optical laser. Current theoretical evidence suggests that nanoparticles can undergo reversible nonhomogenous melting with the formation of a core-shell structure consisting of a liquid outer layer. To date, studies from ensembles of nanoparticles have tentatively suggested that such mechanisms are present. Here we demonstrate imaging transient melting and softening of the acoustic phonon modes of an individual gold nanocrystal, using an X-ray free electron laser. The results demonstrate that the transient melting is reversible and nonhomogenous, consistent with a core-shell model of melting. The results have implications for understanding transient processes in nanoparticles and determining their elastic properties as they undergo phase transitions.
Significance Despite phase transitions, such as melting, being ubiquitous in nature, understanding what occurs at the nanoscale (such as in nanocrystals) has so far remained challenging. With ensemble studies of nanocrystals it is often difficult to discriminate between intrinsic size-dependent properties and effects due to sample size and shape dispersity. Here, using an X-ray free electron laser we image the reversible melting of an individual nanocrystal induced by an ultrashort laser. It is revealed that the melting occurs transiently, repeatably, and inhomogeneously. This is consistent with a core-shell model where the exterior is melted and a solid core remains. These findings reveal, unambiguously, that core-shell melting occurs, which has important implications for understanding nanoscale phenomena.
Stochastic processes are highly relevant in research fields as different as neuroscience, economy, ecology, chemistry, and fundamental physics. However, due to their intrinsic unpredictability, ...stochastic mechanisms are very challenging for any kind of investigations and practical applications. Here we report the deliberate use of stochastic X-ray pulses in two-dimensional spectroscopy to the simultaneous mapping of unoccupied and occupied electronic states of atoms in a regime where the opacity and transparency properties of matter are subject to the incident intensity and photon energy. A readily transferable matrix formalism is presented to extract the electronic states from a dataset measured with the monitored input from a stochastic excitation source. The presented formalism enables investigations of the response of the electronic structure to irradiation with intense X-ray pulses while the time structure of the incident pulses is preserved.
X-ray free-electron lasers (XFELs) provide very intense X-ray pulses suitable for macromolecular crystallography. Each X-ray pulse typically lasts for tens of femtoseconds and the interval between ...pulses is many orders of magnitude longer. Here we describe two novel acoustic injection systems that use focused sound waves to eject picoliter to nanoliter crystal-containing droplets out of microplates and into the X-ray pulse from which diffraction data are collected. The on-demand droplet delivery is synchronized to the XFEL pulse scheme, resulting in X-ray pulses intersecting up to 88% of the droplets. We tested several types of samples in a range of crystallization conditions, wherein the overall crystal hit ratio (e.g., fraction of images with observable diffraction patterns) is a function of the microcrystal slurry concentration. We report crystal structures from lysozyme, thermolysin, and stachydrine demethylase (Stc2). Additional samples were screened to demonstrate that these methods can be applied to rare samples.
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•Acoustic methods inject crystal-containing droplets directly from microplate wells•On-demand acoustic injection uses crystals efficiently without orifices or clogging•Diffraction patterns from crystals measuring several tens of μm are of high quality•Complete datasets can be obtained from fewer than 50,000 crystals
Acoustic droplet ejection provides an automated tool for efficient use of protein crystals in SFX experiments. Roessler et al. used this method to deliver crystal-containing droplets into the XFEL beam to coincide with each X-ray pulse.
A cavity‐based X‐ray free‐electron laser (CBXFEL) is a possible future direction in the development of fully coherent X‐ray sources. CBXFELs consist of a low‐emittance electron source, a magnet ...system with several undulators and chicanes, and an X‐ray cavity. The X‐ray cavity stores and circulates X‐ray pulses for repeated FEL interactions with electron pulses until the FEL reaches saturation. CBXFEL cavities require low‐loss wavefront‐preserving optical components: near‐100%‐reflectivity X‐ray diamond Bragg‐reflecting crystals, outcoupling devices such as thin diamond membranes or X‐ray gratings, and aberration‐free focusing elements. In the framework of the collaborative CBXFEL research and development project of Argonne National Laboratory, SLAC National Accelerator Laboratory and SPring‐8, we report here the design, manufacturing and characterization of X‐ray optical components for the CBXFEL cavity, which include high‐reflectivity diamond crystal mirrors, a diamond drumhead crystal with thin membranes, beryllium refractive lenses and channel‐cut Si monochromators. All the designed optical components have been fully characterized at the Advanced Photon Source to demonstrate their suitability for the CBXFEL cavity application.
The design, manufacturing and characterization of X‐ray optics for a cavity‐based X‐ray free‐electron laser are presented.
Experimental methods that use free‐electron laser (FEL) sources that can deliver short X‐ray pulses below a 10 fs pulse duration and traditional optical lasers are ideal tools for pump–probe ...experiments. However, these new methods also come with a unique set of challenges, such as how to accurately determine temporal overlap between two sources at the femtosecond scale and how to correct for the pulse‐to‐pulse beam property fluctuations of the FEL light derived from the self‐amplified spontaneous emission process. Over the past several years of performing pump–probe experiments at the Linac Coherent Light Source (LCLS), new methods and tools have been developed to improve the ways experimental timing is measured, monitored and scanned. The aim of this article is to present an overview of the most commonly used techniques at LCLS to perform pump–probe‐type experiments.
Techniques developed at LCLS to make optical laser pump–X‐ray probe experiments both robust and easy to implement at ultrafast X‐ray free‐electron lasers are presented.
Coherent nonlinear spectroscopies and imaging in the X-ray domain provide direct insight into the coupled motions of electrons and nuclei with resolution on the electronic length scale and timescale. ...The experimental realization of such techniques will strongly benefit from access to intense, coherent pairs of femtosecond X-ray pulses. We have observed phase-stable X-ray pulse pairs containing more than 3 × 107 photons at 5.9 keV (2.1 Å) with ∼1 fs duration and 2 to 5 fs separation. The highly directional pulse pairs are manifested by interference fringes in the superfluorescent and seeded stimulated manganese Kα emission induced by an X-ray free-electron laser. The fringes constitute the time-frequency X-ray analog of Young’s double-slit interference, allowing for frequency domain X-ray measurements with attosecond time resolution.
We show that light drives large-amplitude structural changes in thin films of the prototypical ferroelectric PbTiO3 via direct coupling to its intrinsic photovoltaic response. Using time-resolved ...x-ray scattering to visualize atomic displacements on femtosecond time scales, photoinduced changes in the unit-cell tetragonality are observed. These are driven by the motion of photogenerated free charges within the ferroelectric and can be simply explained by a model including both shift and screening currents, associated with the displacement of electrons first antiparallel to and then parallel to the ferroelectric polarization direction.
With the rapid development of short-pulse intense laser sources, studies of matter under extreme irradiation conditions enter further unexplored regimes. In addition, an application of X-ray ...Free-Electron Lasers (XFELs) delivering intense femtosecond X-ray pulses, allows to investigate sample evolution in IR pump - X-ray probe experiments with an unprecedented time resolution. Here we present a detailed study of the periodic plasma created from the colloidal crystal. Both experimental data and theory modeling show that the periodicity in the sample survives to a large extent the extreme excitation and shock wave propagation inside the colloidal crystal. This feature enables probing the excited crystal, using the powerful Bragg peak analysis, in contrast to the conventional studies of dense plasma created from bulk samples for which probing with Bragg diffraction technique is not possible. X-ray diffraction measurements of excited colloidal crystals may then lead towards a better understanding of matter phase transitions under extreme irradiation conditions.
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