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A common challenge for pump-probe studies of structural dynamics at X-ray free-electron lasers (XFELs) is the determination of time zero (T0)—the time an optical pulse (e.g., an optical laser) arrives coincidently with the probe pulse (e.g., a XFEL pulse) at the sample position. In some cases, T0 might be extracted from the structural dynamics of the sample's observed response itself, but generally, an independent robust method is required or would be superior to the inferred determination of T0. In this paper, we present how the structural dynamics in ultrafast melting of bismuth can be exploited for a quickly performed, reliable and accurate determination of T0 with a precision below 20 fs and an overall experimental accuracy of 50 fs to 150 fs (estimated). Our approach is potentially useful and applicable for fixed-target XFEL experiments, such as serial femtosecond crystallography, utilizing an optical pump pulse in the ultraviolet to near infrared spectral range and a pixelated 2D photon detector for recording crystallographic diffraction patterns in transmission geometry. In comparison to many other suitable approaches, our method is fairly independent of the pumping wavelength (UV–IR) as well as of the X-ray energy and offers a favorable signal contrast. The technique is exploitable not only for the determination of temporal characteristics of the experiment at the interaction point but also for investigating important conditions affecting experimental control such as spatial overlap and beam spot sizes.

We present a crystallography chip enabling in situ room temperature crystallography at microfocus synchrotron beamlines and X-ray free-electron laser (X-FEL) sources. Compared to other in situ approaches, we observe extremely low background and high diffraction data quality. The chip design is robust and allows fast and efficient loading of thousands of small crystals. The ability to load a large number of protein crystals, at room temperature and with high efficiency, into prescribed positions enables high throughput automated serial crystallography with microfocus synchrotron beamlines. In addition, we demonstrate the application of this chip for femtosecond time-resolved serial crystallography at the Linac Coherent Light Source (LCLS, Menlo Park, California, USA). The chip concept enables multiple images to be acquired from each crystal, allowing differential detection of changes in diffraction intensities in order to obtain high signal-to-noise and fully exploit the time resolution capabilities of XFELs.

Laser spectroscopy, widely applied in physics and chemistry, is extended into the soft x-ray region for the first time. Resonant fluorescence excitation of highly charged ions (HCIs) by soft x-ray free-electron lasers (FELs) shows here the potential for unprecedented precision on photonic transitions hitherto out of reach. The novel experiments combine an electron beam ion trap (EBIT) with the Free-electron LASer at Hamburg (FLASH) to measure resonant fluorescence by trapped HCIs as a function of the laser's wavelength. The present experiments have already reached the performance of conventional soft and hard x-ray spectroscopy. We present the results obtained for three fundamental and theoretically challenging transitions in Li-like ions, namely 1s22s 2S1/2-1s22p 2P1/2 in Fe23+ at 48.6 eV, in Cu26+ at 55.2 eV and 1s22s 2S1/2-1s22p 2P3/2 in Fe23+ at 65.3 eV. The latter demonstrates laser spectroscopy of multiply or HCIs at more than one order of magnitude higher energies than hitherto reported. Resolving power leading to relative precision up to 6 parts-per-million points to the possibility of providing an atomic absolute wavelength standard in this spectral region, which is still lacking. [ABSTRACT FROM AUTHOR]

Single-electron capture in 14 keV q[?]1 Ar15+...18++He collisions is investigated both experimentally and theoretically. Partial cross sections and projectile scattering angle dependencies have been deduced from the target ion recoil momenta measured by the COLTRIMS technique. The comparison with close-coupling results obtained from a two-centre extension of the basis generator method yields good overall agreement, demonstrating the applicability of close-coupling calculations to collision systems involving highly charged ions in charge states up to 18+. [ABSTRACT FROM AUTHOR]