Ultrafast Soft X-ray Probing of Gas Phase Molecular Dynamics

The molecular ability to selectively and efficiently convert sunlight into other forms of energy like heat, bond change, or charge separation is truly remarkable. The decisive steps in these transformations often happen on a femtosecond timescale and require transitions among different electronic states that violate the Born-Oppenheimer approximation (BOA) [1 W. Domcke, D. Yarkony, and H. Köppel, Conical Intersections Electronic Structure, Dynamics &; Spectroscopy, World Scientific, Singapore (2004).[Crossref] , [Google Scholar]]. Non-BOA transitions pose challenges to both theory and experiment. From a theoretical point of view, excited state dynamics and nonadiabatic transitions both are difficult problems [2 F. Plasser, Theor. Chem. Acc. 131, 233902 (2012).[Crossref], [Web of Science ®] , [Google Scholar], 3 J. C. Tully, J. Chem. Phys. 137, 22A301 (2012).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] (see Figure 1(a)). However, the theory on non-BOA dynamics has advanced significantly over the last two decades. Full dynamical simulations for molecules of the size of nucleobases have been possible for a couple of years [4 H. R. Hudock, J. Phys. Chem. A 111, 8500–8508 (2007).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 5 J. J. Szymczak, J. Phys. Chem. A 113, 12686–12693 (2009).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] and allow predictions of experimental observables like photoelectron energy [6 S. Ullrich, Phys. Chem. Chem. Phys. 6, 2796 (2004).[Crossref], [Web of Science ®] , [Google Scholar]] or ion yield [7 H. Tao, J. Chem. Phys. 134, 244306 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–9 M. Assmann, T. Weinacht, and S. Matsika, J. Chem. Phys. 144, 34301 (2016).[Crossref], [Web of Science ®] , [Google Scholar]]. The availability of these calculations for isolated molecules has spurred new experimental efforts to develop methods that are sufficiently different from all optical techniques. For determination of transient molecular structure, femtosecond X-ray diffraction [10 M. P. Minitti, Phys. Rev. Lett. 114, 255501 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 11 J. Küpper, Phys. Rev. Lett. 112, 083002 (2014). [Google Scholar]] and electron diffraction [12 J. Yang, Nat. Commun. 7, 11232 (2016).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] have been implemented on optically excited molecules.     

Femtosecond Structural Dynamics of Proteins

Proteins are the workhorses of living cells, providing essential functions such as structural support, signal transduction, enzymatic catalysis, transport and storage of small ligands. Atomic-resolution structures obtained with conventional X-ray crystallography show proteins essentially as static. In reality, however, proteins move and their motion is crucial for functioning. Although the structure and dynamics of proteins are intimately related, they are not equally well understood. A very large number of protein structures have been determined, but only a few studies have been able to monitor experimentally the dynamics of proteins in real time. In the last two decades, the availability of short (~100 ps) and intense (~10⁹–10¹⁰ photons) X-ray pulses produced by third-generation synchrotrons have allowed the implementation of structural methods like time-resolved X-ray crystallography and time-resolved X-ray solution scattering that have allowed us to monitor protein motion in the nanosecond-to-millisecond timescale [1 K. Moffat, Chem. Rev. 101, 1569–1582 (2001).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–4 J. G. Kim, Acc. Chem. Res. 48, 2200–2208 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. Time-resolved X-ray crystallography has been used to monitor processes such as the migration of a ligand from the protein active site to the surrounding solvent [5 V. Srajer, Science 274, 1726–1729 (1996).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–7 D. Bourgeois, Proc. Natl. Acad. Sci. U. S. A. 100, 8704–8709 (2003).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] or tertiary structural changes associated with allosteric transitions [8 J. E. Knapp, Proc. Natl. Acad. Sci. 103, 7649–7654 (2006).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 9 J. G. Kim, Struct. Dyn. 3, 023610 (2016). [Google Scholar]]. On the other hand, time-resolved X-ray scattering in the so-called wide-angle X-ray scattering (WAXS) region [10 M. Cammarata, Nat. Methods 5, 881–886 (2008).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] has been used to track conformational changes corresponding to large-amplitude protein motions such as the quaternary R-T transition of human hemoglobin [11 M. Cammarata, J. Mol. Biol. 400, 951–962 (2010).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–13 A. Spilotros, Soft Matter 8, 6434–6437 (2012).[Crossref], [Web of Science ®] , [Google Scholar]], the relative motion of bacteriorhodopsin α-helices following retinal isomerization [14 M. Andersson, Structure 17, 1265–1275 (2009).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], or the open-to-close transition in bacterial phytochromes [15 H. Takala, Nature 509, 245–8 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]].     

Seeded Multicolor FEL Pulses: Status and Future Plans

The advent of FEL sources delivering two synchronized pulses of different wavelengths has made available a whole range of novel pump-probe experiments [1 E. Ferrari, Nat. Commun. 7, 10343 (2016).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], allowing the exploration of the dynamics of matter driven to extreme non-equilibrium states by an intense ultrashort X-ray pulse and then probing the sample response at variable time delay with a second pulse [2 E. Allaria, Nat. Commun. 4, 2476 (2013).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]].     

Photon-In/Photon-Out Soft X-ray Spectroscopy at the TPS 45A Beamline

Owing to the current energy crisis and extreme changes in the global climate, there is great interest in finding renewable energy resources. Vast progress has been made in the development of new materials related to renewable energy, and their physical/chemical properties can be tailored by nanostructuring and other advanced synthetic approaches. In many important energy systems, such as solar hydrogen systems, the atomic/electronic structures of materials and fundamental interfacial phenomena of systems critically determine the energy conversion efficiency of materials [1 S. Shen et al., Energy Environ. Sci. 9, 2744 (2016).[Crossref], [Web of Science ®] , [Google Scholar], 2 J. Chen et al., J. Mater. Chem. A 2, 4605 (2014).[Crossref], [Web of Science ®] , [Google Scholar]]. Without knowledge of the fundamental electronic structures of the materials during conversion reactions, better engineering of the material for practical use is difficult. Understanding and controlling the interfaces in energy generation/conversion/storage materials requires in-situ/operando approaches [3 V. Iablokov et al., Nano Lett. 12, 2091 (2012).[Crossref], [Web of Science ®] , [Google Scholar], 4 F. Zheng et al., Nano Lett. 11, 847 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. The Taiwan Photon Source (TPS) Soft X-ray Spectroscopic beamline provides the capabilities for X-ray absorption (XAS) and X-ray emission (XES) spectroscopies, which can be utilized to investigate unoccupied (conduction-band) and occupied (valence-band) electronic states, respectively. Moreover, resonant inelastic X-ray scattering (RIXS) can be used to study intra-band (including d-d or f-f excitations) and inter-band (charge transfer) transitions [5 S. M. Butorin et al., Phys. Rev. Lett. 77, 574 (1996).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 6 P. Kuiper et al., Phys. Rev. Lett. 80, 5204 (1988).[Crossref], [Web of Science ®] , [Google Scholar]]. The former provides details about electronic energy splitting in various crystal fields and the latter involves electron transfer between a metal and a ligand, which determines chemical activity [7 H. Liu, Nano Lett. 7, 1919 (2007).[Crossref], [Web of Science ®] , [Google Scholar], 8 V. Bisogni et al., Phys. Rev. Lett. 114, 096402 (2015).[Crossref], [Web of Science ®] , [Google Scholar]].     

Diverse Application Platform for Hard X-ray Diffraction in SACLA (DAPHNIS)

X-ray free electron lasers (XFELs) produce femtosecond X-ray pulses with nearly full spatial coherence and a peak power in the order of tens of GW [1 P. Emma et al., Nat. Photon. 4, 641–647 (2010).[Crossref], [Web of Science ®] , [Google Scholar], 2 T. Ishikawa et al., Nat. Photon. 6, 540–544 (2012).[Crossref], [Web of Science ®] , [Google Scholar]]. At present, two XFEL facilities, the Linac Coherent Light Source (LCLS) and SPring-8 Angstrom Compact free electron LAser (SACLA), offer research opportunities to scientists from various fields. The novel characteristics of XFELs necessitate new experimental styles, which are very different from those for conventional X-ray sources. Since many users were not familiar with these new styles in the early stage of scientific applications, user-friendly experimental systems were necessary to boost the XFEL applications into a state of practical use. XFELs are now producing unique results in, for example, structural biology [3 H. N. Chapman et al., Nature 470, 73–77 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–6 M. Suga et al., Nature 517, 99–103 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], nonlinear X-ray optics [7 K. Tamasaku et al., Nat. Photon. 8, 313–316 (2014).[Crossref], [Web of Science ®] , [Google Scholar], 8 H. Yoneda et al., Nature 524, 446–449 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], ultrafast physics and chemistry [9 W. Zhang et al., Nature 509, 345–348 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–11 K. H. Kim et al., Nature 518, 385–389 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], and high-energy-density science [12 S. M. Vinko et al., Nature 482, 59–62 (2012).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]].     

Data Analysis Environment for X-ray Free-Electron Laser Experiments at SACLA

X-ray free-electron lasers (XFELs) with full spatial coherence, extreme brilliance, and ultra-fast pulse duration [1 P. Emma et al., Nat. Photon. 4, 641–647 (2010).[Crossref], [Web of Science ®] , [Google Scholar], 2 T. Ishikawa et al., Nat. Photon. 6, 540–544 (2012).[Crossref], [Web of Science ®] , [Google Scholar]] allow the investigation of complex phenomena in physics, chemistry, and biology with angstrom and femtosecond resolutions. In particular, a concept of “diffraction before destruction” [3 R. Neutze et al., Nature 406, 752–757 (2000).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] has been demonstrated for serial femtosecond crystallography (SFX) [4 H. N. Chapman et al., Nature 470, 73–77 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 5 S. Boutet et al., Science 337, 362–364 (2012).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] and coherent diffractive imaging (CDI) [6 M. M. Seibert et al., Nature 470, 78–81 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. Using femto-second XFEL pulses, diffraction data are collected before radiation damage to samples has time to occur. Since samples are exchanged for each XFEL pulse, shot-to-shot data acquisition (DAQ) is mandatory to correlate the recorded data with the sample characteristics. The shot-to-shot DAQ must be synchronized with the repetition rate of the XFEL source, typically several tens to one hundred Hz for the machine based on normal-conducting accelerators. Shot-to-shot recording of XFEL pulse characteristics is also essential because they fluctuate due to the stochastic nature of a self-amplified spontaneous emission (SASE). We must carefully analyze a huge data set taking the fluctuation into account.     

Simulation and Experimental Study of Wavefront Measurement Accuracy of the Pencil-Beam Method

Ultra-bright and high-coherence X-rays are now being used in synchrotron radiation facilities and X-ray free electron laser facilities. X-ray focusing techniques are essential to take full advantage of these excellent X-ray light sources. To meet the strong demand, high-quality X-ray focusing optics have been developed owing to the advancement of ultraprecision machining and measurement. State-of-the-art refractive lenses [1 C.G. Schroer, Applied Physics Letters 87, 124103 (2005).[Crossref], [Web of Science ®] , [Google Scholar]], zone plates [2 T. Chen, Optics Express 19, 19919 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], and Laue lenses [3 H. Yan, Optics Express 19, 15069 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] can be used to achieve X-ray focusing to a spot a few tens of nanometers.     

MXCuBE3: A New Era of MX-Beamline Control Begins

The outstanding success of structural biology within the last two decades is closely related to the development and evolution of macromolecular crystallography (MX) beamlines. Indeed, many of today's synchrotron-based MX experimental sessions aim for fast but rigorous evaluations and data collections from very large numbers of samples [1 A. Joachimiak, Current Opinion in Structural Biology 19, 573–584 (2009).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–7 R. L. Owen, Archives of Biochemistry and Biophysics 602, 21–31 (2016).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. To facilitate this, sample changing on most MX beamlines is now carried out by robots and the centering of a crystal in the X-ray beam to micrometer precision is now automatically performed using either optical or diffraction-based techniques [8 D. Nurizzo, Acta Cryst. D 72, 966–975 (2016).[Crossref] , [Google Scholar]]. Once a crystal is centered, users have a wide array of options at their disposal to prepare any given experiment. This includes: X-ray fluorescence (XRF) [9 G. A. Leonard, Journal of Applied Crystallography 42, 333–335 (2009).[Crossref], [Web of Science ®] , [Google Scholar]] analysis to confirm the presence of anomalous scatterers in crystals; X-ray absorption near-edge scans (XANES) to determine the best X-ray wavelengths for MAD/SAD data collection [10 W. A. Hendrickson, Methods Enzymol. 276, 494–523 (1997).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]; and the probing of the diffraction properties of crystals to determine the best crystal, or area of a crystal [11 M. W. Bowler, Acta Cryst. D 66, 855–864 (2010).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], for data collection. All of these operations are now also automated, as is the collection of the final diffraction data set either from single or multiple crystals and the subsequent data analysis and reduction.     

If You Can Get a Crystal Structure,Why Bother with Anything Else?

Since the first crystal structures were determined by the Braggs just over 100 years ago, crystallography has rapidly evolved in parallel with developments in photon, neutron, and electron sources to become the “go-to” technique for structure-function studies. It can provide atomic resolution structural information on an entire three-dimensional molecular or crystalline structure and is used from the study of bulk phase materials through to individual protein molecules [1 E.F. Garman, Science 343, 1102–1108 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 2 J.A.K. Howard and M.R. Probert, Science 343, 1098–1102 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]].     

Advancement of Hard X-ray Nano-focusing Ellipsoidal Mirror at SPring-8

Ellipsoidal mirror optics can produce a smaller, two-dimensional focus with diffraction-limited properties than is possible when using mirror optics in Kirkpatrick–Baez (K–B) geometry [1 P. Kirkpatrick and A.V. Baez, Journal of the Optical Society of America 38, 766–773 (1948).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. This is because ellipsoidal focusing mirrors can be designed such that they have a larger numerical aperture in the sagittal focusing direction as compared to that in the meridional focusing direction. Although ellipsoidal focusing mirrors have this crucial advantage over K–B optics, K–B optics are widely utilized as micro-/nano-focusing devices [2 H. Mimura, Nature Physics 6, 122–125 (2010).[Crossref], [Web of Science ®] , [Google Scholar]–8 H. Mimura, Nature Communications 5, 3539 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] in synchrotron radiation facilities and X-ray free electron laser facilities [9 P. Emma, Nature Photonics 4, 641–647 (2010).[Crossref], [Web of Science ®] , [Google Scholar], 10 T. Ishikawa, Nature Photonics 6, 540–544 (2012).[Crossref], [Web of Science ®] , [Google Scholar]]. Figure 1 shows a schematic of focusing mirror optics; Figure 1(a) shows the ellipsoidal mirror and Figure 1(b) the K–B mirror arrangement. In K–B geometry, two mirrors with a one-dimensionally curved surface, such as an elliptical cylinder, are orthogonally arranged in tandem to reflect and focus light independently in a direction perpendicular to each other under grazing-incidence conditions. Ellipsoidal focusing mirrors, which can generate a two-dimensional focusing beam by a single reflection, have a highly sloped surface with a two-dimensional aspherical shape, when compared to elliptical-cylinder mirrors that are used for line-focusing in K–B geometry. In addition, surface shapes of nano-focusing mirrors must be fabricated with nanometer-level accuracy. Therefore, fabrication of ellipsoidal nano-focusing mirrors is extremely difficult. There are no reports on ellipsoidal nano-focusing mirrors in the hard X-ray region with superior performances to provide diffraction-limited beams.     

First X-ray Absorption Spectroscopy at SSRP in 1974

The study of X-ray absorption spectroscopy (XAS) began at an exciting time in science. In the early years of the twentieth century, wave mechanics, X-ray diffraction, X-ray scattering from non-crystalline materials, electron diffraction, and XAS were all being developed simultaneously. Many XAS concepts and experimental techniques advanced in parallel with these other subjects; however, the difficulty of obtaining good XAS data from conventional X-ray tubes limited the field to a potentially interesting minor subject [1 R. Stumm von Bordwehr, Ann. Phys. Fr., 14, 377–466 (1989).[Crossref], [Web of Science ®] , [Google Scholar], 2 F. W. Lytle, J. Synchrotron Rad., 6, 123–134 (1999).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]].     

Multilayer Laue Lens: A Brief History and Current Status

X-rays are intrinsically capable of being used for the study of non-periodic objects with atomic resolution, with high penetration, in applied electromagnetic fields, and in fluids and gases. For direct imaging via nanofocused X-ray beams, reflective [1 K. Yamauchi, Journal of Physics: Condensed Matter 23(39), 394206 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], refractive [2 C.G. Schroer, Applied Physics Letters 87(12), 124103–3 (2005).[Crossref], [Web of Science ®] , [Google Scholar]], and diffractive [3 K. Burkhard, Journal of Physics: Condensed Matter 23(8), 083002 (2011).[Crossref], [Web of Science ®] , [Google Scholar], 4 J. Kirz, C. Jacobsen, and M. Howells, Quarterly Reviews of Biophysics 28(01), 33–130 (1995).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] optics are used in various approaches for high-resolution imaging. Diffractive X-ray optics are endowed with the highest numerical aperture, in principle allowing focusing of X-rays to sub-nanometer dimensions. Lithographically produced Fresnel zone plates (FZP) find broad deployment around the globe, in both nanofocusing and full-field imaging approaches, and have, for many years, been workhorse optics in both synchrotron-based and laboratory-based X-ray imaging systems [4 J. Kirz, C. Jacobsen, and M. Howells, Quarterly Reviews of Biophysics 28(01), 33–130 (1995).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. A FZP consists of a series of radially symmetric rings, which are known as Fresnel zones, which alternate between transparent and opaque. Radiation traversing into the FZP diffracts around the opaque zones, which are placed in an arrangement where light constructively interferes at the focal plane.     

Ambient-Pressure X-ray Photoelectron Spectroscopy to Characterize the Solid/Liquid Interface: Probing the Electrochemical Double Layer

Ambient-pressure X-ray photoelectron spectroscopy (APXPS) has contributed greatly to a wide range of research fields, including environmental science [1 H. Bluhm, Journal of Electron Spectroscopy and Related Phenomena 177, 71–84 (2010).[Crossref], [Web of Science ®] , [Google Scholar]], catalysis [2 D.E. Starr et al., Chemical Society Reviews 42, 5833–5857 (2013).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], and electrochemistry [3 E.J. Crumlin, H. Bluhm, and Z. Liu, Journal of Electron Spectroscopy and Related Phenomena 190, 84–92 (2013).[Crossref], [Web of Science ®] , [Google Scholar]], to name a few. The use of this technique at synchrotron facilities primarily focused on probing the solid/gas interface; however, it quickly advanced to the probing of liquid/vapor interfaces [4 D.E. Starr et al., Physical Chemistry Chemical Physics 10, 3093–3098 (2008).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 5 M.A. Brown et al., Physical Chemistry Chemical Physics 10, 4778–4784 (2008).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] and solid/liquid interfaces through an X-ray-transparent window [6 J. Kraus et al., Nanoscale 6, 14394–14403 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–8 T. Masuda et al., Appl Phys Lett 103 (2013).[Crossref], [Web of Science ®] , [Google Scholar]]. Most recently, combining APXPS with “Tender” X-rays (~2.5 keV to 8 keV) on beamline 9.3.1 at the Advanced Light Source in Lawrence Berkeley National Laboratory (which can generate photoelectrons with much longer inelastic mean free paths) has enabled us to probe the solid/liquid interface without needing a window [9 S. Axnanda et al., Scientific Reports 5 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. This innovation allows us to probe interfacial chemistries of electrochemically controlled solid/liquid interfaces undergoing charge transfer reactions [9 S. Axnanda et al., Scientific Reports 5 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. These advancements have transitioned APXPS from a traditional surface science tool to an essential interface science technique.     

Ultrafast Electronic and Molecular Dynamics Induced by Ultrashort FEL Pulses

In recent years, short wavelength free electron lasers (FELs) have opened up access to ultrafast electronic and structural dynamics in matter. Currently, four FEL facilities are in operation in the world. FLASH [1 W. Ackermann, Nat. Photonics 1, 336 (2007).[Crossref], [Web of Science ®] , [Google Scholar]] in Germany and FERMI [2 P. Emma, Nat. Photonics 4, 641 (2010).[Crossref], [Web of Science ®] , [Google Scholar]] in Italy cover the range from extreme ultraviolet (EUV) to soft X-rays, while LCLS [3 T. Ishikawa, Nat. Photonics 6, 540 (2012).[Crossref], [Web of Science ®] , [Google Scholar]] in the U.S. and SACLA [4 E. Allaria, Nat. Photonics 6, 699 (2012).[Crossref], [Web of Science ®] , [Google Scholar]] in Japan provide pulses in the hard X-ray regime. In addition, an upgrade version of SCSS [5 T. Shintake, Nat. Photonics 2, 555 (2008).[Crossref], [Web of Science ®] , [Google Scholar]], nicknamed SCSS+, has also just started user operation as a beamline of SACLA [6 See http://xfel.riken.jp/eng/users/index.html [Google Scholar]]. These FELs deliver coherent pulses combining unprecedented power densities up to ~10²⁰ W/cm² and extremely short pulse durations down to a few femtoseconds. The intense coherent FEL pulse focused down to ~1 μm² makes single-shot diffractive imaging of nano-crystals or even non-crystallized bio-samples as well as other small objects a reality. Time-resolved spectroscopic and structural studies on the timescale of femtoseconds, having FEL pulses as a probe, allow us to probe electrons and atoms in action. Additionally, since FEL pulses are in a new regime of intensity, they are opening up new research fields that exploit the interaction between intense short wavelength pulses and matter, leading to matter at extremely high energy. Relevant theories dealing with such extreme conditions are also rapidly growing.     

Sesame workshop/school on bioinformatics and structural modelling

The potential of X-rays for the non-invasive investigation of the interior of bulky samples has long been recognized and their penetration depth is presently widely exploited [1 Hounsfield, G. N. 1973. Br J Radiol, 46: 1016–1022. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. Although initially third generation synchrotron sources were almost exclusively the realm of academic scientific experiments, the use of synchrotron light for industrial research is becoming increasingly important and relevant for both technology development and non-destructive testing, in particular when the requirements in terms of spatial, temporal, and density resolution are exceptional.     

Advancements and Application of Microsecond Synchrotron X-ray Footprinting at the Advanced Light Source

The method of synchrotron X-ray protein footprinting (XF-MS) is used to determine protein conformational changes, folding, protein-protein and protein-ligand interactions, providing information which is often difficult to obtain using X-ray crystallography and other common structural biology methods [1 G. Xu and M.R. Chance, Chemical Reviews 107, 3514–3543 (2007).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–3 V.N. Bavro, Biochem Soc Trans 43, 983–994 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. The technique uses comparative in situ labeling of solvent-accessible side chains by highly reactive hydroxyl radicals (?OH) in buffered aqueous solution under different assay conditions. In regions where a protein is folded or binds a partner, these ?OH susceptible sites are inaccessible to solvent, and therefore protected from labeling. The ?OH are generated by the ionization of water using high-flux-density X-rays. High-flux density is a key factor for XF-MS labeling because obtaining an adequate steady-state concentration of hydroxyl radical within a short irradiation time is necessary to minimize radiation-induced secondary damage and also to overcome various scavenging reactions that reduce the yield of labeled side chains.     

Surface Science Studies with Free Electron Lasers: Real-Time Observations of Electronic Structure Changes during Reactions

New light sources based on linear accelerators such as FLASH at DESY in Hamburg, the first free-electron laser in the extreme ultraviolet (XUV) and soft X-ray regime, which started user operation in 2005 [1 W. Ackermann, Nature Photonics 1, 336–342 (2007).[Crossref], [Web of Science ®] , [Google Scholar]], the Linac Coherent Light Source LCLS in Stanford [2 P. Emma, Nature Photonics 4, 641–647 (2010).[Crossref], [Web of Science ®] , [Google Scholar]], and SACLA at Spring-8 in Japan [3 T. Ishikawa, Nature Photonics 6, 540–544 (2012).[Crossref], [Web of Science ®] , [Google Scholar]], as X-ray lasers dedicated to the hard X-ray regime down to below 1 Å in wavelength, or FERMI at ELETTRA in Trieste [4 E. Allaria, Nature Photonics 6, 699–704 (2012).[Crossref], [Web of Science ®] , [Google Scholar]] as the first fully externally seeded free electron laser also operating in the XUV and soft X-ray regime, provide ultrashort, extremely powerful, short wavelength pulses with unprecedented coherence properties. With the European XFEL in Hamburg, the Swiss FEL at PSI in Villigen, Switzerland, and the PAL-XFEL in Pohang, Korea, three more FELs are expected to produce first light by the end of 2016 and the beginning of 2017, respectively.     

Coherent soft X-ray magnetic scattering

X-ray sources are exceptional tools for studying the structure of matter down to atomic-length scales, but across a wide range of fields there are samples that have remained notoriously difficult to study, such as airborne particles, particles in solution, membrane proteins, and macromolecular complexes. The advancement of imaging techniques to address these elusive samples has been a big motivation for constructing new X-ray light sources. Fourth-generation light sources, commonly called X-ray free-electron lasers (XFELs) [1 Madey, J. 1971. Journal of Applied Physics, 42: 1906–1913. [Crossref], [Web of Science ®] , [Google Scholar]], represent a huge step forward, with upwards of nine orders of magnitude increase in peak brightness for hard X-rays. As of 2012, four such XFELs are already productively operational (in Germany [2 Ackermann, W. 2007. Nature Photonics, 1: 336–342. [Crossref], [Web of Science ®] , [Google Scholar]], the U.S. [3 Emma, P. 2010. Nature Photonics, 4: 641–647. [Crossref], [Web of Science ®] , [Google Scholar]], Japan [4 Ishikawa, T. 2012. Nature Photonics, 6: 540–544. [Crossref], [Web of Science ®] , [Google Scholar]], and Italy [5 Allaria, E. 2012. Nature Photonics, 6: 699–704. [Crossref], [Web of Science ®] , [Google Scholar]]), with at least five more planned for the next 10 years. These lasers produce femtosecond pulses of extremely intense coherent radiation through the positive feedback between a co-moving electron bunch and the radiation it emits when they traverse an extended undulator. This process creates remarkably strong, tunable probes that will undoubtedly change the way we examine nanoscale structure and dynamics.     

Fourth User Workshop on High-Power Lasers at the Linac Coherent Light Source

The fourth international user workshop focusing on high-power lasers at the Linac Coherent Light Source (LCLS) was held in Menlo Park, CA, USA, on October 3–4, 2016 [1 R. Falcone, S. Glenzer, and S. Hau-Riege, Synchrotron Radiation News 27(2), 56–58 (2014).[Taylor &; Francis Online] , [Google Scholar]–3 C. Bolme, S. Glenzer, and A. Fry, Synchrotron Radiation News 29(2), 14–17 (2016).[Taylor &; Francis Online] , [Google Scholar]]. The workshop was co-organized by Los Alamos National Laboratory and SLAC National Accelerator Laboratory (SLAC), and garnered the attendance of more than 110 scientists. Participants discussed the warm dense matter and high-pressure science that is being conducted using high-power lasers at the LCLS Matter in Extreme Conditions (MEC) endstation. During the past year, there have been seven journal articles published from research at the MEC instrument [4 L. B. Fletcher et al., Review of Scientific Instruments 87(11), 11E524 (2016).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–10 P. Sperling et al., Physical Review Letters 115(11), 115001 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. The specific topics discussed at this workshop were experimental highlights from the past year, current status and future commissioning of MEC capabilities, and future facility upgrades that will enable the expanded science reach of the facility.