THA —  FEL Applications   (24-Aug-17   08:30—10:00)
Chair: A.H. Lumpkin, Fermilab, Batavia, Illinois, USA
Paper Title Page
Observations of Fast Structural Changes with an X-ray FEL: Dynamics Studies on Photoactivated Proteins at SACLA  
  • K. Tono
    JASRI/SPring-8, Hyogo, Japan
  X-ray FELs (XFELs) paved the way for exploring ultrafast structural dynamics in a biological macromolecule. Time-resolved protein crystallography with an XFEL now can reach a resolution of the order of femtosecond. One of the most promising techniques for time-resolved measurement is serial femtosecond crystallography (SFX). We have developed an experimental system for time-resolved SFX at SACLA*. This system has been applied for visualizing structural changes in a photoactivated macromolecule such as bacteriorhodopsin (bR)** or photosystem II (PSII)***. In the application to bR, diffraction measurements cover a wide range of timescales from nanoseconds to milliseconds to fully access the structural transitions in the photocycle. The structural data at more than ten time points provided a cascade of structural changes after photoactivation of the retinal chromophore. This 'movie' clearly shows how bR transports protons through a cell membrane against a chemical-potential gradient. This paper gives an overview of the experimental instruments and techniques for studying ultrafast protein dynamics with XFEL, and recent applications at SACLA.
* K. Tono et al., J. Synchrotron Rad. 22, 532 (2015).
** E. Nango et al., Science 354, 1552 (2016).
*** M. Suga et al., Nature 543, 131 (2017).
Four-Wave Mixing Using Extreme Ultraviolet Transient Gratings at FERMI FEL  
  • F. Bencivenga, F. Capotondi, R. Cucini, L. Foglia, C. Masciovecchio, R. Mincigrucci, E. Pedersoli, E. Principi, A. Simoncig
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  Four-wave mixing (FWM) processes are exploited in the optical domain in a large array of scientific and technological applications. The extension of this approach to the XUV and X-ray range was theoretically conceived,* but not experimentally pursued because of the lack of photon sources with enough brightness and coherence. This situation has changed with the advent of FELs, in particular those stabilized by seeding processes. In this context, the XUV pulses delivered by FERMI have been used to experimentally demonstrate the FWM response stimulated by XUV transient gratings.** More recently the 'twin-seed' double-colour FEL mode of FERMI has been employed in a two-colour XUV FWM experiment.*** These results provide grounds to build up the sophisticated experiments envisioned by theoreticians,* which could provide access to high energy/high-wavevector excitations, with elemental selectivity and nano to atomic spatial resolution. Capabilities that can be exploited in different fields, ranging from thermal transport dynamics in nanoelectronic devices to charge transfer processes in molecules.
* S. Tanaka and S. Mukamel, Phys. Rev. Lett., 2002, 89, 043001
** F. Bencivenga et al., Nature, 2015, 520, 205
*** F. Bencivenga et al., Faraday Discuss., 2014, 171, 487
Two-Temperature Equilibration in Warm Dense Hydrogen Measured With X-Ray Scattering from the Linac Coherent Light Source  
  • L.B. Fletcher
    SLAC, Menlo Park, California, USA
  Funding: This work was supported by the DOE/SC/FES under contract No. SF00515 and supported under FWP 100182 and DOE/SC/BES, Materials Sciences and Engineering Division, contract DE-AC02-76SF00515.
Understanding the properties of warm dense hydrogen plasmas is critical for modeling stellar and planetary interiors, as well as for inertial confinement fusion (ICF) experiments. Knowledge of thermodynamic properties of hydrogen in a fusion environment furthers our ability to accurately model complex systems essential to ICF. Of central importance are the electron-ion collision and equilibration times that determine the microscopic properties in a high energy-density state. Spectrally and angularly resolved X-ray scattering measurements from fs-laser heated hydrogen have resolved the picosecond evolution and energy relaxation from a two-temperature plasma towards thermodynamic equilibrium in the warm dense matter regime. The interaction of rapidly heated cryogenic hydrogen irradiated by a 400-nm, 5x1017-W/cm2, 70-fs laser is visualized with ultra-bright 5.5-keV x-ray pulses from the Linac Coherent Light Source (LCLS) in a 1-Hz repetition-rate pump probe setting. We demonstrate that the energy relaxation is faster than many classical binary collision theories that use ad hoc cutoff parameters used in the Landau-Spitzer determination of the Coulomb logarithm.