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Structural Dynamics (Melville, N.Y.)

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https://www.readbyqxmd.com/read/28852689/time-resolved-soft-x-ray-absorption-spectroscopy-in-transmission-mode-on-liquids-at-mhz-repetition-rates
#1
Mattis Fondell, Sebastian Eckert, Raphael M Jay, Christian Weniger, Wilson Quevedo, Johannes Niskanen, Brian Kennedy, Florian Sorgenfrei, Daniel Schick, Erika Giangrisostomi, Ruslan Ovsyannikov, Katrin Adamczyk, Nils Huse, Philippe Wernet, Rolf Mitzner, Alexander Föhlisch
We present a setup combining a liquid flatjet sample delivery and a MHz laser system for time-resolved soft X-ray absorption measurements of liquid samples at the high brilliance undulator beamline UE52-SGM at Bessy II yielding unprecedented statistics in this spectral range. We demonstrate that the efficient detection of transient absorption changes in transmission mode enables the identification of photoexcited species in dilute samples. With iron(II)-trisbipyridine in aqueous solution as a benchmark system, we present absorption measurements at various edges in the soft X-ray regime...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28852688/euv-stimulated-emission-from-mgo-pumped-by-fel-pulses
#2
Philippe Jonnard, Jean-Michel André, Karine Le Guen, Meiyi Wu, Emiliano Principi, Alberto Simoncig, Alessandro Gessini, Riccardo Mincigrucci, Claudio Masciovecchio, Olivier Peyrusse
Stimulated emission is a fundamental process in nature that deserves to be investigated and understood in the extreme ultra-violet (EUV) and x-ray regimes. Today, this is definitely possible through high energy density free electron laser (FEL) beams. In this context, we give evidence for soft-x-ray stimulated emission from a magnesium oxide solid target pumped by EUV FEL pulses formed in the regime of travelling-wave amplified spontaneous emission in backward geometry. Our results combine two effects separately reported in previous works: emission in a privileged direction and existence of a material-dependent threshold for the stimulated emission...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28852687/heterodyne-x-ray-diffuse-scattering-from-coherent-phonons
#3
M Kozina, M Trigo, M Chollet, J N Clark, J M Glownia, A C Gossard, T Henighan, M P Jiang, H Lu, A Majumdar, D Zhu, D A Reis
Here, we report Fourier-transform inelastic x-ray scattering measurements of photoexcited GaAs with embedded ErAs nanoparticles. We observe temporal oscillations in the x-ray scattering intensity, which we attribute to inelastic scattering from coherent acoustic phonons. Unlike in thermal equilibrium, where inelastic x-ray scattering is proportional to the phonon occupation, we show that the scattering is proportional to the phonon amplitude for coherent states. The wavevectors of the observed phonons extend beyond the excitation wavevector...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28852686/solving-the-jitter-problem-in-microwave-compressed-ultrafast-electron-diffraction-instruments-robust-sub-50-fs-cavity-laser-phase-stabilization
#4
M R Otto, L P René de Cotret, M J Stern, B J Siwick
We demonstrate the compression of electron pulses in a high-brightness ultrafast electron diffraction instrument using phase-locked microwave signals directly generated from a mode-locked femtosecond oscillator. Additionally, a continuous-wave phase stabilization system that accurately corrects for phase fluctuations arising in the compression cavity from both power amplification and thermal drift induced detuning was designed and implemented. An improvement in the microwave timing stability from 100 fs to 5 fs RMS is measured electronically, and the long-term arrival time stability ([Formula: see text]10 h) of the electron pulses improves to below our measurement resolution of 50 fs...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28795080/electron-lattice-energy-relaxation-in-laser-excited-thin-film-au-insulator-heterostructures-studied-by-ultrafast-mev-electron-diffraction
#5
K Sokolowski-Tinten, X Shen, Q Zheng, T Chase, R Coffee, M Jerman, R K Li, M Ligges, I Makasyuk, M Mo, A H Reid, B Rethfeld, T Vecchione, S P Weathersby, H A Dürr, X J Wang
We apply time-resolved MeV electron diffraction to study the electron-lattice energy relaxation in thin film Au-insulator heterostructures. Through precise measurements of the transient Debye-Waller-factor, the mean-square atomic displacement is directly determined, which allows to quantitatively follow the temporal evolution of the lattice temperature after short pulse laser excitation. Data obtained over an extended range of laser fluences reveal an increased relaxation rate when the film thickness is reduced or the Au-film is capped with an additional insulator top-layer...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28795079/towards-shot-noise-limited-diffraction-experiments-with-table-top-femtosecond-hard-x-ray-sources
#6
Marcel Holtz, Christoph Hauf, Jannick Weisshaupt, Antonio-Andres Hernandez Salvador, Michael Woerner, Thomas Elsaesser
Table-top laser-driven hard x-ray sources with kilohertz repetition rates are an attractive alternative to large-scale accelerator-based systems and have found widespread applications in x-ray studies of ultrafast structural dynamics. Hard x-ray pulses of 100 fs duration have been generated at the Cu K α wavelength with a photon flux of up to 10(9) photons per pulse into the full solid angle, perfectly synchronized to the sub-100-fs optical pulses from the driving laser system. Based on spontaneous x-ray emission, such sources display a particular noise behavior which impacts the sensitivity of x-ray diffraction experiments...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28781982/influence-of-cathode-geometry-on-electron-dynamics-in-an-ultrafast-electron-microscope
#7
Shaozheng Ji, Luca Piazza, Gaolong Cao, Sang Tae Park, Bryan W Reed, Daniel J Masiel, Jonas Weissenrieder
Efforts to understand matter at ever-increasing spatial and temporal resolutions have led to the development of instruments such as the ultrafast transmission electron microscope (UEM) that can capture transient processes with combined nanometer and picosecond resolutions. However, analysis by UEM is often associated with extended acquisition times, mainly due to the limitations of the electron gun. Improvements are hampered by tradeoffs in realizing combinations of the conflicting objectives for source size, emittance, and energy and temporal dispersion...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28713843/probing-ultrafast-changes-of-spin-and-charge-density-profiles-with-resonant-xuv-magnetic-reflectivity-at-the-free-electron-laser-fermi
#8
C Gutt, T Sant, D Ksenzov, F Capotondi, E Pedersoli, L Raimondi, I P Nikolov, M Kiskinova, S Jaiswal, G Jakob, M Kläui, H Zabel, U Pietsch
We report the results of resonant magnetic XUV reflectivity experiments performed at the XUV free-electron laser FERMI. Circularly polarized XUV light with the photon energy tuned to the Fe M2,3 edge is used to measure resonant magnetic reflectivities and the corresponding Q-resolved asymmetry of a Permalloy/Ta/Permalloy trilayer film. The asymmetry exhibits ultrafast changes on 240 fs time scales upon pumping with ultrashort IR laser pulses. Depending on the value of the wavevector transfer Qz , we observe both decreasing and increasing values of the asymmetry parameter, which is attributed to ultrafast changes in the vertical spin and charge density profiles of the trilayer film...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28653022/robust-reconstruction-of-time-resolved-diffraction-from-ultrafast-streak-cameras
#9
Daniel S Badali, R J Dwayne Miller
In conjunction with ultrafast diffraction, streak cameras offer an unprecedented opportunity for recording an entire molecular movie with a single probe pulse. This is an attractive alternative to conventional pump-probe experiments and opens the door to studying irreversible dynamics. However, due to the "smearing" of the diffraction pattern across the detector, the streaking technique has thus far been limited to simple mono-crystalline samples and extreme care has been taken to avoid overlapping diffraction spots...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28612041/structural-and-dynamic-insights-into-the-role-of-conformational-switching-in-the-nuclease-activity-of-the-xanthomonas-albilineans-cas2-in-crispr-mediated-adaptive-immunity
#10
Donghyun Ka, Suji Hong, Ugeene Jeong, Migyeong Jeong, Nayoung Suh, Jeong-Yong Suh, Euiyoung Bae
Clustered regularly interspaced short palindromic repeats (CRISPRs) and CRISPR-associated (Cas) proteins constitute a microbial, adaptive immune system countering invading nucleic acids. Cas2 is a universal Cas protein found in all types of CRISPR-Cas systems, and its role is implicated in new spacer acquisition into CRISPR loci. In subtype I-C CRISPR-Cas systems, Cas2 proteins are metal-dependent double-stranded DNA (dsDNA) nucleases, and a pH-dependent conformational transition has been proposed as a prerequisite for catalytic action...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28580369/transient-process-spectroscopy-for-the-direct-observation-of-inter-molecular-photo-dissociation
#11
Sena Hashimoto, Atsushi Yabushita, Izumi Iwakura
Transient process spectroscopy has previously been thought to be applicable only to the analysis of intra-molecular processes. Two metal ion bridges used in the present work have allowed us to visualize real-time variations of the molecular vibration frequencies during photo-disproportionation inside bimolecule aggregates, which directly shows transient inter-molecular reactions.
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28580368/monitoring-nonadiabatic-avoided-crossing-dynamics-in-molecules-by-ultrafast-x-ray-diffraction
#12
Markus Kowalewski, Kochise Bennett, Shaul Mukamel
We examine time-resolved X-ray diffraction from molecules in the gas phase which undergo nonadiabatic avoided-crossing dynamics involving strongly coupled electrons and nuclei. Several contributions to the signal are identified, representing (in decreasing strength) elastic scattering, contributions of the electronic coherences created by nonadiabatic couplings in the avoided crossing regime, and inelastic scattering. The former probes the charge density and delivers direct information on the evolving molecular geometry...
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28503632/ultrafast-x-ray-diffraction-probe-of-terahertz-field-driven-soft-mode-dynamics-in-srtio3
#13
M Kozina, T van Driel, M Chollet, T Sato, J M Glownia, S Wandel, M Radovic, U Staub, M C Hoffmann
We use ultrafast X-ray pulses to characterize the lattice response of SrTiO3 when driven by strong terahertz fields. We observe transient changes in the diffraction intensity with a delayed onset with respect to the driving field. Fourier analysis reveals two frequency components corresponding to the two lowest energy zone-center optical modes in SrTiO3. The lower frequency mode exhibits clear softening as the temperature is decreased while the higher frequency mode shows slight temperature dependence.
September 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28868325/active-control-of-bright-electron-beams-with-rf-optics-for-femtosecond-microscopy
#14
J Williams, F Zhou, T Sun, Z Tao, K Chang, K Makino, M Berz, P M Duxbury, C-Y Ruan
A frontier challenge in implementing femtosecond electron microscopy is to gain precise optical control of intense beams to mitigate collective space charge effects for significantly improving the throughput. Here, we explore the flexible uses of an RF cavity as a longitudinal lens in a high-intensity beam column for condensing the electron beams both temporally and spectrally, relevant to the design of ultrafast electron microscopy. Through the introduction of a novel atomic grating approach for characterization of electron bunch phase space and control optics, we elucidate the principles for predicting and controlling the phase space dynamics to reach optimal compressions at various electron densities and generating conditions...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28868324/from-structure-to-structural-dynamics-ahmed-zewail-s-legacy
#15
Majed Chergui, John Meurig Thomas
In this brief tribute to Ahmed Zewail, we highlight and place in the historical context, several of the major achievements that he and his colleagues have made in Femtochemistry (of which he was the principal instigator) and his introduction of ultrafast electron scattering, diffraction, microscopy and spectroscopy. By achieving a sub-picosecond temporal resolution, coupled with a picometer spatial resolution, he revolutionised our understanding of the corpus of chemical, physical, biological and materials science systems...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28852685/ultrafast-atomic-scale-visualization-of-acoustic-phonons-generated-by-optically-excited-quantum-dots
#16
Giovanni M Vanacore, Jianbo Hu, Wenxi Liang, Sergio Bietti, Stefano Sanguinetti, Fabrizio Carbone, Ahmed H Zewail
Understanding the dynamics of atomic vibrations confined in quasi-zero dimensional systems is crucial from both a fundamental point-of-view and a technological perspective. Using ultrafast electron diffraction, we monitored the lattice dynamics of GaAs quantum dots-grown by Droplet Epitaxy on AlGaAs-with sub-picosecond and sub-picometer resolutions. An ultrafast laser pulse nearly resonantly excites a confined exciton, which efficiently couples to high-energy acoustic phonons through the deformation potential mechanism...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28852684/preface-to-special-topic-ultrafast-structural-dynamics-a-tribute-to-ahmed-h-zewail
#17
Majed Chergui
No abstract text is available yet for this article.
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28713842/femtosecond-time-resolved-x-ray-absorption-spectroscopy-of-anatase-tio2-nanoparticles-using-xfel
#18
Yuki Obara, Hironori Ito, Terumasa Ito, Naoya Kurahashi, Stephan Thürmer, Hiroki Tanaka, Tetsuo Katayama, Tadashi Togashi, Shigeki Owada, Yo-Ichi Yamamoto, Shutaro Karashima, Junichi Nishitani, Makina Yabashi, Toshinori Suzuki, Kazuhiko Misawa
The charge-carrier dynamics of anatase TiO2 nanoparticles in an aqueous solution were studied by femtosecond time-resolved X-ray absorption spectroscopy using an X-ray free electron laser in combination with a synchronized ultraviolet femtosecond laser (268 nm). Using an arrival time monitor for the X-ray pulses, we obtained a temporal resolution of 170 fs. The transient X-ray absorption spectra revealed an ultrafast Ti K-edge shift and a subsequent growth of a pre-edge structure. The edge shift occurred in ca...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28713841/design-and-implementation-of-an-optimal-laser-pulse-front-tilting-scheme-for-ultrafast-electron-diffraction-in-reflection-geometry-with-high-temporal-resolution
#19
Francesco Pennacchio, Giovanni M Vanacore, Giulia F Mancini, Malte Oppermann, Rajeswari Jayaraman, Pietro Musumeci, Peter Baum, Fabrizio Carbone
Ultrafast electron diffraction is a powerful technique to investigate out-of-equilibrium atomic dynamics in solids with high temporal resolution. When diffraction is performed in reflection geometry, the main limitation is the mismatch in group velocity between the overlapping pump light and the electron probe pulses, which affects the overall temporal resolution of the experiment. A solution already available in the literature involved pulse front tilt of the pump beam at the sample, providing a sub-picosecond time resolution...
July 2017: Structural Dynamics (Melville, N.Y.)
https://www.readbyqxmd.com/read/28713840/ultrafast-kinetics-of-linkage-isomerism-in-na2-fe-cn-5no-aqueous-solution-revealed-by-time-resolved-photoelectron-spectroscopy
#20
Azhr A Raheem, Martin Wilke, Mario Borgwardt, Nicholas Engel, Sergey I Bokarev, Gilbert Grell, Saadullah G Aziz, Oliver Kühn, Igor Yu Kiyan, Christoph Merschjann, Emad F Aziz
The kinetics of ultrafast photoinduced structural changes in linkage isomers is investigated using Na2[Fe(CN)5NO] as a model complex. The buildup of the metastable side-on configuration of the NO ligand, as well as the electronic energy levels of ground, excited, and metastable states, has been revealed by means of time-resolved extreme UV (XUV) photoelectron spectroscopy in aqueous solution, aided by theoretical calculations. Evidence of a short-lived intermediate state in the isomerization process and its nature are discussed, finding that the complete isomerization process occurs in less than 240 fs after photoexcitation...
July 2017: Structural Dynamics (Melville, N.Y.)
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