Short laser pulses of femtosecond time scales are in high demand in order to explore the fast electron dynamics in light-matter interactions. Here, the authors demonstrated the compression of free electron laser pulses in the extreme ultraviolet range by using a chirped pulse amplification technique.
Photon sources, such as table-top lasers, synchrotron X-rays and free-electron lasers (FELs), can be used to explore and understand the structure of materials through photon-matter interactions. Short wavelength and coherent photons generated, when relativistic electrons travel through undulator, from FELs are tunable and compressible to few femtosecond pulses to take snapshots of structures in order to study the time-dependent interactions and dynamics of different materials. These facilities are becoming increasingly popular in diverse research fields, because of their tunability and high spatial and temporal resolution.
In this collection, we showcase recent articles published in Nature Communications on FEL generation and characterization and their application in fundamental studies of light-matter interaction. These research papers include FEL instrumentation and techniques, investigations on photoionization and ultrafast processes in atomic and molecular physics, chemical and physical properties of condensed matter systems, and probing of structure and dynamics of biological samples. This collection highlights the increasingly significant role FELs are having on research across a diverse range of subject areas and Nature Communications’ role as a suitable platform in publishing such multidisciplinary works.
Phase-sensitive measurements are important to gain insights of light-matter interactions and require phase-controlled pulses. Here the authors demonstrate the phase control and interferometric autocorrelation on a free electron laser using SASE pulse pair created with a split and delay unit.
Free electron laser beam profile characterization is usually performed separately from the actual measurements and this leads to considerable uncertainty in the results. Here the authors demonstrate the simultaneous measurement of the FEL beam profile with the experiment by using integrated gratings.
X-ray spectroscopy is a tool used for the investigation of aqueous solutions but the strong absorption of water means that very thin liquid sheets are needed for accurate analysis. Here the authors produce free-flowing liquid sheets 2 orders of magnitude thinner than sheets obtained with existing techniques.
X-ray free-electron lasers, important light sources for materials research, suffer from shot-to-shot fluctuations that necessitate complex diagnostics. Here, the authors apply machine learning to accurately predict pulse properties, using parameters that can be acquired at high-repetition rates.
X-ray optics are notoriously challenging to fabricate due to the strict tolerances that result from the short wavelength of radiation. Here, Seibothet al. carefully quantify aberrations in complex X-ray lenses and correct them with an easy-to-fabricate broadband phase plate.
Short X-ray pulses from free-electron lasers enable coherent diffractive imaging of noncrystalline objects such as single molecules. Here, the authors reconstructing full image information from a single-shot diffraction pattern by using two sufficiently separated objects to act as references for each other.
The occurrence of thermodynamically metastable nanoparticles determines the particle growth in nature, but capturing them is experimentally challenging. Barke et al. identify the three-dimensional shape of metastable silver nanoparticles in gas phase, characterized by X-ray free-electron laser.
X-ray free-electron laser is a power probe for materials, but it is challenging to measure the spectro-temporal characters of individual pulses. Here, De Ninno et al.implement an interferometric method allowing one to characterize and control the ultrashort XUV pulses seeded by a femtosecond laser.
Two-colour X-ray pulses from free-electron lasers can be used to probe ultrafast dynamics, but the total power is a fraction of the saturation power. Here, Marinelli et al. use twin electron bunches to reach full saturation power and increase the two-colour intensity by an order of magnitude at hard-X-ray energies.
Few-femtosecond synchronization at free-electron lasers is key for nearly all experimental applications, stable operation and future light source development. Here, Schulz et al. demonstrate all-optical synchronization of the soft X-ray FEL FLASH to better than 30 fs and illustrate a pathway to sub-10 fs.
Free electron lasers are emerging as important tools for nonlinear spectroscopy in the X-ray regime. Here the authors demonstrate the second order coherence of a seeded FEL source that may be useful for measurements in quantum optics.
Existing methods to extract structural information from single-molecule scattering measurements require large number of photons per image. Here the authors discuss a method to reconstruct the structure of a molecule from X-ray scattering data by using only three photons per image.
XFELs in structural biology
X-ray free electron lasers are increasingly available for use in macromolecular structure determination. Here, the authors describe the successful use of selenium single-wavelength anomalous diffraction data to calculate experimentally derived phases.
Structural identification of electron transfer dissociation products in mass spectrometry using infrared ion spectroscopy
Mass spectrometry is a leading method used for sequencing peptides and proteins by fragmentation followed by analysis of the sequence fragments. Here, the authors use infrared spectroscopy to characterize the structures of peptide fragments formed during electron transfer dissociation.
Diacylglycerol kinase is a small bacterial membrane-bound trimer that catalyses diacylglycerol conversion to phosphatidic acid. Here, the authors solve the crystal structure of the kinase bound to a lipid substrate and an ATP analogue, and show that the active site arose through convergent evolution.
Crystal structure of a multi-domain human smoothened receptor in complex with a super stabilizing ligand
Smoothened receptors (SMO) play a key role in the Hedgehog signalling pathway. Here the authors present the structure of a multi-domain human SMO with a rationally designed stabilizing ligand bound in the transmembrane domain of the receptor, and propose a model for SMO activation.
Imaging live cells at nanometre resolution is challenging because radiation damage kills the cells during exposure. Here, the authors overcome this difficulty in a ‘diffraction before destruction’ experiment using an X-ray laser and record signal to 4 nm resolution on a free-flying cell.
Structural characterization of a highly-potent V3-glycan broadly neutralizing antibody bound to natively-glycosylated HIV-1 envelope
Structure determination of glycosylated HIV-1 envelope (Env) trimers complexed with broadly neutralizing antibodies (bNAbs) promotes a better understanding of bNAb epitopes. Here the authors present the structures of natively-glycosylated Env in complex with the highly-potent bNAb BG18, which is of interest for HIV-1 vaccine development.
Structure of CPV17 polyhedrin determined by the improved analysis of serial femtosecond crystallographic data
Serial femtosecond crystallography and the use of X-ray free-electron lasers (XFEL) promise to revolutionize structural biology. Here, the authors describe refinements that reduce the redundancy required to obtain quality XFEL data and report a 1.75-Å structure—not obtainable by synchrotron radiation—using less than 6,000 crystals.
Capturing an initial intermediate during the P450nor enzymatic reaction using time-resolved XFEL crystallography and caged-substrate
Using photosensitive caged-compound for femtosecond crystallography at X-ray free electron lasers would allow the structure determination of reaction intermediates. Here the authors demonstrate the feasibility of this approach with a caged NO-compound and present the initial NO-bound intermediate structure of cytochrome P450 nitric oxide reductase.
The structures of amyloid fibres are currently primarily studied through solid state NMR and cryo-EM. Here the authors present a free-standing graphene support device that allows diffraction imaging of non-crystalline amyloid fibrils with single X-ray pulses from an X-ray free-electron laser.
Localized chemical events such as the breakage of a bond between a protein and a ligand may trigger a global protein conformational change. Here, the authors use an X-ray free-electron laser to track the motion of myoglobin in response to photoinduced ligand release, and observe a picosecond proteinquake.
Lipidic cubic phase injector is a viable crystal delivery system for time-resolved serial crystallography
Serial femtosecond crystallography using X-ray free-electron lasers has huge potential for time-resolved structural experiments. Here, the authors present a structure of the light-driven proton pump bacteriorhodopsin using these techniques.
The new European X-Ray Free-Electron Laser (EuXFEL) is the first XFEL that generates X-ray pulses with a megahertz inter-pulse spacing. Here the authors demonstrate that high-quality and damage-free protein structures can be obtained with the currently available 1.1 MHz repetition rate pulses using lysozyme as a test case and furthermore present a β-lactamase structure.
Multi-wavelength anomalous diffraction de novo phasing using a two-colour X-ray free-electron laser with wide tunability
X-ray free-electron lasers produce bright femtosecond X-ray pulses. Here, the authors use a two-colour X-ray free-electron laser beam for simultaneous two-wavelength data collection and show that protein structures can be determined with multiple wavelength anomalous dispersion phasing, which is important for difficult-to-phase projects.
The European X-ray free-electron laser (EuXFEL) in Hamburg is the first megahertz (MHz) repetition rate XFEL. Here the authors use lysozyme crystals and microcrystals from jack bean proteins and demonstrate that damage-free high quality data can be collected at a MHz repetition rate.
FELs in condensed matter
Widely tunable two-colour seeded free-electron laser source for resonant-pump resonant-probe magnetic scattering
Two-colour X-ray free electron laser is a powerful tool for pump–probe measurements, but currently constrained by limited tunability. Here, Ferrari et al. develop a configuration that allows tuning both the pump and the probe to specific electronic excitations, providing element selectivity.
It is essential to understand the effect of molecular vibration on charge transport for better design of molecular electronics. Here, the authors test two benchmark aromatic motifs and show how the coupling between π electrons and molecular vibration is affected by molecular edge topology.
Interatomic Coulombic decay (ICD) is a relaxation of an atom in a weakly bound environment by the transfer of excess energy to ionize the neighbouring atom. Here the authors observe intra-Rydberg ICD in neon clusters, which is a decay that involves the ionization of Rydberg atoms in the cluster.
Towards ultrafast dynamics with split-pulse X-ray photon correlation spectroscopy at free electron laser sources
X-ray photon correlation spectroscopy has been mainly used to measure slow dynamics using synchrotron sources. Here the authors demonstrate the split-and- delay pulse set-up to study nanosecond dynamics of gold nanoparticles using XPCS with free electron laser pulses.
The dynamics of liquid water is rich due to its complex, highly disordered hydrogen-bond network, which hasn’t been fully understood. Perakis et al. measure water dynamics at sub-100 fs and show that it cannot be described by simple thermal motion due to the build-up of tetrahedral structures upon supercooling.
Probing ultrafast ππ*/nπ* internal conversion in organic chromophores via K-edge resonant absorption
Many photo-induced processes such as photosynthesis occur in organic molecules, but their femtosecond excited-state dynamics are difficult to track. Here, the authors exploit the element and site selectivity of soft X-ray absorption to sensitively follow the ultrafast ππ*/nπ* electronic relaxation of hetero-organic molecules.
Group IV–VI materials often exist in a state near an electronic or structural phase transition. Here, the authors use ultrafast X-ray scattering to show that coupling of band-edge electrons and phonons causes the ferroelectric instability observed in lead telluride.
Coherent structural trapping through wave packet dispersion during photoinduced spin state switching
Ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remain challenging to describe since electronic/nuclear configurations are coupled. Here the authors use time-resolved X-ray absorption spectroscopy to probe the light-induced spin-state trapping dynamics of [Fe(bpy)3]2+beyond the Born-Oppenheimer approximation.
In BaFe2As2, the lattice couples strongly to the magnetic and electronic degrees of freedom, providing a way to control them. Here, by means of time-resolved X-ray scattering, the authors measure rapid lattice oscillations, which can induce changes in the material’s electronic and magnetic properties.
Ligand-induced substrate steering and reshaping of [Ag2(H)]+ scaffold for selective CO2 extrusion from formic acid
Designing catalysts and understanding the influence of ligands for particular transformations remains a highly challenging task. Here, the authors show that bisphosphine ligands can alter the geometry of the active site in silver catalysts, driving protonation and ultimately extrusion of carbon dioxide from formic acid.
Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses
Photoinduced electron transfer in solvated molecular assemblies occurs on the ultrafast timescale before full electronic and geometric relaxation take place. Here Canton et al.monitor this out-of-equilibrium process in a donor–acceptor bimetallic assembly using an X-ray free-electron laser.
Interactions between reactive excited states of molecular photocatalysts and surrounding solvent can dictate reaction pathways, but are not readily accessible to conventional spectroscopic methods. Here the authors use diffuse X-ray scattering and theory to study the atomistic solvation dynamics of a photoexcited di-iridium complex in acetonitrile.
The effect of dense plasma environment on the energy levels of an ion is usually described in terms of a lowering of its continuum level. Here the authors present an isochoric-heating experiment to measure and compare continuum lowering in single-species and mixture plasmas to provide insights for models.
Our understanding of shock metamorphism and thus the collision of planetary bodies is limited by a dependence on ex situ analyses. Here, the authors perform in situ analysis on shocked-produced densified glass and show that estimates of impactor size based on traditional techniques are likely inflated.
FELs in atomic and molecular physics
The timescale of isomerization in molecules involving ultrafast migration of constituent atoms is difficult to measure. Here the authors report that sub-100 fs isomerization time on acetylene dication in lower electronic states is not possible and point to misinterpretation of recent experimental results.
Proton migration in the acetylene cation is commonly used as a model to study isomerisation dynamics. Here, the authors use X-ray pump-probe experiments to study this process, and show that isomerization occurs significantly faster than expected—within the first 12 femtoseconds following core ionization.
Two-color X-ray pulses with controlled time delay allow exciting one site of a molecule and then probing a different site of the same molecule with femtosecond resolution. Here, the authors use this hetero-site pump-probe technique to study charge redistribution and dissociation of the xenon difluoride molecule.
Electrons in atoms exhibit many-body collective behaviours that can be studied by highbrightness X-rays from FELs. Here, the authors examine two-photon above threshold ionization of xenon and find that nonlinearities in the response uncover that more than one state underpins the 4dgiant resonance.
Exploring the photoionization process leads to better understanding of the fundamental interactions between light and matter. Here the authors show the non-dipole contribution in the form of asymmetric photoelectron angular distribution from the ionization of argon atoms and ions.
Availability of intense hard X-ray pulses allows exploration of multiple ionization effects in heavier elements. Here, the authors measure the complex charge state distributions of xenon and found a reasonable agreement by comparing with the model including the relativistic and resonance effects.
The first steps in photochemical processes involve changes in electronic and geometric structure on extremely short timescales. Here, the authors report femtosecond dynamics in prototypical acetylacetone, by pump-probe photoexcitation-photoemission experiments and static and dynamics calculations.