TY - JOUR A1 - Enquist, Henrik A1 - Navirian, Hengameh A1 - Nueske, Ralf A1 - von Korff Schmising, Clemens A1 - Jurgilaitis, Andrius A1 - Herzog, Marc A1 - Bargheer, Matias A1 - Sondhauss, Peter A1 - Larsson, Joergen T1 - Subpicosecond hard x-ray streak camera using single-photon counting N2 - We have developed and characterized a hard x-ray accumulating streak camera that achieves subpicosecond time resolution by using single-photon counting. A high repetition rate of 2 kHz was achieved by use of a readout camera with built-in image processing capabilities. The effects of sweep jitter were removed by using a UV timing reference. The use of single-photon counting allows the camera to reach a high quantum efficiency by not limiting the divergence of the photoelectrons. Y1 - 2010 UR - http://www.opticsinfobase.org/ U6 - https://doi.org/10.1364/OL.35.003219 SN - 0146-9592 ER - TY - JOUR A1 - Herzog, Marc A1 - Leitenberger, Wolfram A1 - Shayduk, Roman A1 - van der Veen, Renske Marjan A1 - Milne, Chris J. A1 - Johnson, Steven Lee A1 - Vrejoiu, Ionela A1 - Alexe, Marin A1 - Hesse, Dietrich A1 - Bargheer, Matias T1 - Ultrafast manipulation of hard x-rays by efficient Bragg switches N2 - We experimentally demonstrate efficient switching of the hard x-ray Bragg reflectivity of a SrRuO3 /SrTiO3 superlattice by optical excitation of large-amplitude coherent acoustic superlattice phonons. The rocking curve changes drastically on a 1 ps timescale. The (0 0 116) reflection is almost extinguished (Delta R/R-0=-0.91), while the (0 0 118) reflection increases by more than an order of magnitude (Delta R/R-0=24.1). The change of the x-ray structure factor depends nonlinearly on the phonon amplitude, allowing manipulation of the x-ray response on a timescale considerably shorter than the phonon period. Numerical simulations for a superlattice with slightly changed geometry and realistic parameters predict a switching-contrast ratio Delta R/R-0 of 700 with high reflectivity. Y1 - 2010 UR - http://apl.aip.org/ U6 - https://doi.org/10.1063/1.3402773 SN - 0003-6951 ER - TY - JOUR A1 - Navirian, Hengameh A. A1 - Herzog, Marc A1 - Goldshteyn, J. A1 - Leitenberger, Wolfram A1 - Vrejoiu, Ionella A1 - Khakhulin, D. A1 - Wulff, M. A1 - Shayduk, Roman A1 - Gaal, P. A1 - Bargheer, Matias T1 - Shortening x-ray pulses for pump-probe experiments at synchrotrons JF - Journal of applied physics N2 - We implemented an experimental scheme for ultrafast x-ray diffraction at storage rings based on a laser-driven Bragg-switch that shortens the x-ray pulses emitted from an undulator. The increased time-resolution is demonstrated by observing changes of intensity, position and width of the diffraction peaks of a La(0.7)Sr(0.3)MnO(3)/SrTiO(3) superlattice sample after optical excitation, i.e., by quantitatively measuring the propagation of an expansion wave through the sample. These experimental transients with timescales of 35 to 60 ps evidence a reduction of the x-ray pulse duration by a factor of two. Y1 - 2011 U6 - https://doi.org/10.1063/1.3601057 SN - 0021-8979 VL - 109 IS - 12 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Shayduk, Roman A1 - Navirian, Hengameh A1 - Leitenberger, Wolfram A1 - Goldshteyn, Jevgenij A1 - Vrejoiu, Ionela A1 - Weinelt, Martin A1 - Gaal, Peter A1 - Herzog, Marc A1 - von Korff Schmising, Clemens A1 - Bargheer, Matias T1 - Nanoscale heat transport studied by high-resolution time-resolved x-ray diffraction JF - New journal of physics : the open-access journal for physics N2 - We report on synchrotron-based high-repetition rate ultrafast x-ray diffraction (UXRD) experiments monitoring the transport of heat from an epitaxial La(0.7)Sr(0.3)MnO(3)/SrTiO(3) superlattice (SL) into the substrate on timescales from 100 ps to 4 mu s. Transient thermal lattice expansion was determined with an accuracy of 10(-7), corresponding to a sensitivity to temperature changes down to 0.01 K. We follow the heat flow within the SL and into the substrate after the impulsive laser heating leads to a small temperature rise of Delta T = 6 K. The transient lattice temperature can be simulated very well using the bulk heat conductivities. This contradicts the interpretation of previous UXRD measurements, which predicted a long-lasting expansion of SrRuO(3) for more than 200 ps. The disagreement could be resolved by assuming that the heat conductivity changes in the first hundred picoseconds. Y1 - 2011 U6 - https://doi.org/10.1088/1367-2630/13/9/093032 SN - 1367-2630 VL - 13 IS - 11 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Herzog, Marc A1 - Schick, Daniel A1 - Gaal, P. A1 - Shayduk, Roman A1 - von Korff Schmising, Clemens A1 - Bargheer, Matias T1 - Analysis of ultrafast X-ray diffraction data in a linear-chain model of the lattice dynamics JF - Applied physics : A, Materials science & processing N2 - We present ultrafast X-ray diffraction (UXRD) experiments which sensitively probe impulsively excited acoustic phonons propagating in a SrRuO3/SrTiO3 superlattice and further into the substrate. These findings are discussed together with previous UXRD results (Herzog et al. in Appl. Phys. Lett. 96, 161906, 2010; Woerner et al. in Appl. Phys. A 96, 83, 2009; v. Korff Schmising in Phys. Rev. B 78, 060404(R), 2008 and in Appl. Phys. B 88, 1, 2007) using a normal-mode analysis of a linear-chain model of masses and springs, thus identifying them as linear-response phenomena. We point out the direct correspondence of calculated observables with X-ray signals. In this framework the complex lattice motion turns out to result from an interference of vibrational eigenmodes of the coupled system of nanolayers and substrate. UXRD in principle selectively measures the lattice motion occurring with a specific wavevector, however, each Bragg reflection only measures the amplitude of a delocalized phonon mode in a spatially localized region, determined by the nanocomposition of the sample or the extinction depth of X-rays. This leads to a decay of experimental signals although the excited modes survive. Y1 - 2012 U6 - https://doi.org/10.1007/s00339-011-6719-z SN - 0947-8396 VL - 106 IS - 3 SP - 489 EP - 499 PB - Springer CY - New York ER - TY - JOUR A1 - Herzog, Marc A1 - Bojahr, Andre A1 - Goldshteyn, J. A1 - Leitenberger, Wolfram A1 - Vrejoiu, I. A1 - Khakhulin, D. A1 - Wulff, M. A1 - Shayduk, Roman A1 - Gaal, P. A1 - Bargheer, Matias T1 - Detecting optically synthesized quasi-monochromatic sub-terahertz phonon wavepackets by ultrafast x-ray diffraction JF - Applied physics letters N2 - We excite an epitaxial SrRuO3 thin film transducer by a pulse train of ultrashort laser pulses, launching coherent sound waves into the underlying SrTiO3 substrate. Synchrotron-based x-ray diffraction (XRD) data exhibiting separated sidebands to the substrate peak evidence the excitation of a quasi-monochromatic phonon wavepacket with sub-THz central frequency. The frequency and bandwidth of this sound pulse can be controlled by the optical pulse train. We compare the experimental data to combined lattice dynamics and dynamical XRD simulations to verify the coherent phonon dynamics. In addition, we observe a lifetime of 130 ps of such sub-THz phonons in accordance with the theory. KW - acoustic waves KW - epitaxial layers KW - phonon dispersion relations KW - terahertz waves KW - thin film devices KW - X-ray diffraction Y1 - 2012 U6 - https://doi.org/10.1063/1.3688492 SN - 0003-6951 VL - 100 IS - 9 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Gaal, P. A1 - Schick, Daniel A1 - Herzog, Marc A1 - Bojahr, Andre A1 - Shayduk, Roman A1 - Goldshteyn, J. A1 - Navirian, Hengameh A. A1 - Leitenberger, Wolfram A1 - Vrejoiu, Ionela A1 - Khakhulin, D. A1 - Wulff, M. A1 - Bargheer, Matias T1 - Time-domain sampling of x-ray pulses using an ultrafast sample response JF - Applied physics letters N2 - We employ the ultrafast response of a 15.4 nm thin SrRuO3 layer grown epitaxially on a SrTiO3 substrate to perform time-domain sampling of an x-ray pulse emitted from a synchrotron storage ring. Excitation of the sample with an ultrashort laser pulse triggers coherent expansion and compression waves in the thin layer, which turn the diffraction efficiency on and off at a fixed Bragg angle during 5 ps. This is significantly shorter than the duration of the synchrotron x-ray pulse of 100 ps. Cross-correlation measurements of the ultrafast sample response and the synchrotron x-ray pulse allow to reconstruct the x-ray pulse shape. Y1 - 2012 U6 - https://doi.org/10.1063/1.4769828 SN - 0003-6951 VL - 101 IS - 24 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Bojahr, Andre A1 - Schick, Daniel A1 - Märten, Lena A1 - Herzog, Marc A1 - Vrejoiu, Ionela A1 - von Korff Schmising, Clemens A1 - Milne, Chris A1 - Johnson, Steven Lee A1 - Bargheer, Matias T1 - Comparing the oscillation phase in optical pump-probe spectra to ultrafast x-ray diffraction in the metal-dielectric SrRuO3/SrTiO3 superlattice JF - Physical review : B, Condensed matter and materials physics N2 - We measured the ultrafast optical response of metal-dielectric superlattices by broadband all-optical pump-probe spectroscopy. The observed phase of the superlattice mode depends on the probe wavelength, making assignments of the excitation mechanism difficult. Ultrafast x-ray diffraction data reveal the true oscillation phase of the lattice which changes as a function of the excitation fluence. This result is confirmed by the fluence dependence of optical transients. We set up a linear chain model of the lattice dynamics and successfully simulated the broadband optical reflection by unit-cell resolved calculation of the strain-dependent dielectric functions of the constituting materials. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevB.85.224302 SN - 1098-0121 VL - 85 IS - 22 PB - American Physical Society CY - College Park ER - TY - THES A1 - Herzog, Marc T1 - Structural dynamics of photoexcited nanolayered perovskites studied by ultrafast x-ray diffraction T1 - Untersuchung der Strukturdynamik photoangeregter Nanoschicht-Perowskite mittels ultraschneller Röntgenbeugung N2 - This publication-based thesis represents a contribution to the active research field of ultrafast structural dynamics in laser-excited nanostructures. The investigation of such dynamics is mandatory for the understanding of the various physical processes on microscopic scales in complex materials which have great potentials for advances in many technological applications. I theoretically and experimentally examine the coherent, incoherent and anharmonic lattice dynamics of epitaxial metal-insulator heterostructures on timescales ranging from femtoseconds up to nanoseconds. To infer information on the transient dynamics in the photoexcited crystal lattices experimental techniques using ultrashort optical and x-ray pulses are employed. The experimental setups include table-top sources as well as large-scale facilities such as synchrotron sources. At the core of my work lies the development of a linear-chain model to simulate and analyze the photoexcited atomic-scale dynamics. The calculated strain fields are then used to simulate the optical and x-ray response of the considered thin films and multilayers in order to relate the experimental signatures to particular structural processes. This way one obtains insight into the rich lattice dynamics exhibiting coherent transport of vibrational energy from local excitations via delocalized phonon modes of the samples. The complex deformations in tailored multilayers are identified to give rise to highly nonlinear x-ray diffraction responses due to transient interference effects. The understanding of such effects and the ability to precisely calculate those are exploited for the design of novel ultrafast x-ray optics. In particular, I present several Phonon Bragg Switch concepts to efficiently generate ultrashort x-ray pulses for time-resolved structural investigations. By extension of the numerical models to include incoherent phonon propagation and anharmonic lattice potentials I present a new view on the fundamental research topics of nanoscale thermal transport and anharmonic phonon-phonon interactions such as nonlinear sound propagation and phonon damping. The former issue is exemplified by the time-resolved heat conduction from thin SrRuO3 films into a SrTiO3 substrate which exhibits an unexpectedly slow heat conductivity. Furthermore, I discuss various experiments which can be well reproduced by the versatile numerical models and thus evidence strong lattice anharmonicities in the perovskite oxide SrTiO3. The thesis also presents several advances of experimental techniques such as time-resolved phonon spectroscopy with optical and x-ray photons as well as concepts for the implementation of x-ray diffraction setups at standard synchrotron beamlines with largely improved time-resolution for investigations of ultrafast structural processes. This work forms the basis for ongoing research topics in complex oxide materials including electronic correlations and phase transitions related to the elastic, magnetic and polarization degrees of freedom. N2 - Diese publikationsbasierte Dissertation ist ein Beitrag zu dem aktuellen Forschungsgebiet der ultraschnellen Strukturdynamik in laserangeregten Nanostrukturen. Die Erforschung solcher Vorgänge ist unabdingbar für ein Verständnis der vielseitigen physikalischen Prozesse auf mikroskopischen Längenskalen in komplexen Materialien, welche enorme Weiterentwicklungen für technologische Anwendungen versprechen. Meine theoretischen und experimentellen Untersuchungen betrachten kohärente, inkohärente und anharmonische Gitterdynamiken in epitaktischen Metal-Isolator-Heterostrukturen auf Zeitskalen von Femtosekunden bis Nanosekunden. Um Einsichten in solche transienten Prozesse in laserangeregten Kristallen zu erhalten, werden experimentelle Techniken herangezogen, die ultrakurze Pulse von sichtbarem Licht und Röntgenstrahlung verwenden. Ein zentraler Bestandteil meiner Arbeit ist die Entwicklung eines Linearkettenmodells zur Simulation und Analyse der laserinitiierten Atombewegungen. Die damit errechneten Verzerrungsfelder werden anschließend verwendet, um die Änderung der optischen und Röntgeneigenschaften der betrachteten Dünnfilm- und Vielschichtsysteme zu simulieren. Diese Rechnungen werden dann mit den experimentellen Daten verglichen, um die experimentellen Signaturen mit errechneten strukturellen Prozessen zu identifizieren. Dadurch erhält man Einsicht in die vielseitige Gitterdynamiken, was z.B. einen kohärenten Transport der Vibrationsenergie von lokal angeregten Bereichen durch delokalisierte Phononenmoden offenbart. Es wird gezeigt, dass die komplexen Deformationen in maßgeschneiderten Vielschichtsystemen hochgradig nichtlineare Röntgenbeugungseffekte auf Grund von transienten Interferenzerscheinungen verursachen. Das Verständnis dieser Prozesse und die Möglichkeit, diese präzise zu simulieren, werden dazu verwendet, neuartige ultraschnelle Röntgenoptiken zu entwerfen. Insbesondere erläutere ich mehrere Phonon-Bragg-Schalter-Konzepte für die effiziente Erzeugung ultrakurzer Röntgenpulse, die in zeitaufgelösten Strukturanalysen Anwendung finden. Auf Grund der Erweiterung der numerischen Modelle zur Beschreibung von inkohärenter Phononenausbreitung und anharmonischer Gitterpotentiale decken diese ebenfalls die aktuellen Themengebiete von Wärmetransport auf Nanoskalen und anharmonischer Phonon-Phonon-Wechselwirkung (z.B. nichtlineare Schallausbreitung und Phononendämpfung) ab. Die erstere Thematik wird am Beispiel der zeitaufgelösten Wärmeleitung von einem dünnen SrRuO3-Film in ein SrTiO3-Substrat behandelt, wobei ein unerwartet langsamer Wärmetransport zu Tage tritt. Außerdem diskutiere ich mehrere Experimente, die auf Grund der sehr guten Reproduzierbarkeit durch die numerischen Modelle starke Gitteranharmonizitäten in dem oxidischen Perowskit SrTiO3 bezeugen. Diese Dissertation erarbeitet zusätzlich verschiedene Weiterentwicklungen von experimentellen Methoden, wie z.B. die zeitaufgelöste Phononenspektroskopie mittels optischer Photonen und Röntgenphotonen, sowie Konzepte für die Umsetzung von Röntgenbeugungsexperimenten an Standard-Synchrotronquellen mit stark verbesserter Zeitauflösung für weitere Studien von ultraschnellen Strukturvorgängen. KW - ultraschnelle Röntgenbeugung KW - Phononen KW - epitaktisch KW - ultrafast x-ray diffraction KW - phonons KW - epitaxial Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-62632 ER - TY - JOUR A1 - Herzog, Marc A1 - Schick, Daniel A1 - Leitenberger, Wolfram A1 - Shayduk, Roman A1 - van der Veen, Renske M. A1 - Milne, Christopher J. A1 - Johnson, Steven Lee A1 - Vrejoiu, Ionela A1 - Bargheer, Matias T1 - Tailoring interference and nonlinear manipulation of femtosecond x-rays JF - New journal of physics : the open-access journal for physics N2 - We present ultrafast x-ray diffraction (UXRD) experiments on different photoexcited oxide superlattices. All data are successfully simulated by dynamical x-ray diffraction calculations based on a microscopic model, that accounts for the linear response of phonons to the excitation laser pulse. Some Bragg reflections display a highly nonlinear strain dependence. The origin of linear and two distinct nonlinear response phenomena is discussed in a conceptually simpler model using the interference of envelope functions that describe the diffraction efficiency of the average constituent nanolayers. The combination of both models facilitates rapid and accurate simulations of UXRD experiments. Y1 - 2012 U6 - https://doi.org/10.1088/1367-2630/14/1/013004 SN - 1367-2630 VL - 14 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER -