@article{GaalSchickHerzogetal.2012, author = {Gaal, P. and Schick, Daniel and Herzog, Marc and Bojahr, Andre and Shayduk, Roman and Goldshteyn, J. and Navirian, Hengameh A. and Leitenberger, Wolfram and Vrejoiu, Ionela and Khakhulin, D. and Wulff, M. and Bargheer, Matias}, title = {Time-domain sampling of x-ray pulses using an ultrafast sample response}, series = {Applied physics letters}, volume = {101}, journal = {Applied physics letters}, number = {24}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.4769828}, pages = {4}, year = {2012}, abstract = {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.}, language = {en} } @article{GaalSchickHerzogetal.2014, author = {Gaal, Peter and Schick, Daniel and Herzog, Marc and Bojahr, Andre and Shayduk, Roman and Goldshteyn, Jevgeni and Leitenberger, Wolfram and Vrejoiu, Ionela and Khakhulin, Dmitry and Wulff, Michael and Bargheer, Matias}, title = {Ultrafast switching of hard X-rays}, series = {Journal of synchrotron radiation}, volume = {21}, journal = {Journal of synchrotron radiation}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0909-0495}, doi = {10.1107/S1600577513031949}, pages = {380 -- 385}, year = {2014}, abstract = {A new concept for shortening hard X-ray pulses emitted from a third-generation synchrotron source down to few picoseconds is presented. The device, called the PicoSwitch, exploits the dynamics of coherent acoustic phonons in a photo-excited thin film. A characterization of the structure demonstrates switching times of <= 5 ps and a peak reflectivity of similar to 10(-3). The device is tested in a real synchrotron-based pump-probe experiment and reveals features of coherent phonon propagation in a second thin film sample, thus demonstrating the potential to significantly improve the temporal resolution at existing synchrotron facilities.}, language = {en} } @article{HerzogBojahrGoldshteynetal.2012, author = {Herzog, Marc and Bojahr, Andre and Goldshteyn, J. and Leitenberger, Wolfram and Vrejoiu, I. and Khakhulin, D. and Wulff, M. and Shayduk, Roman and Gaal, P. and Bargheer, Matias}, title = {Detecting optically synthesized quasi-monochromatic sub-terahertz phonon wavepackets by ultrafast x-ray diffraction}, series = {Applied physics letters}, volume = {100}, journal = {Applied physics letters}, number = {9}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.3688492}, pages = {4}, year = {2012}, abstract = {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.}, language = {en} } @article{HerzogLeitenbergerShayduketal.2010, author = {Herzog, Marc and Leitenberger, Wolfram and Shayduk, Roman and van der Veen, Renske Marjan and Milne, Chris J. and Johnson, Steven Lee and Vrejoiu, Ionela and Alexe, Marin and Hesse, Dietrich and Bargheer, Matias}, title = {Ultrafast manipulation of hard x-rays by efficient Bragg switches}, issn = {0003-6951}, doi = {10.1063/1.3402773}, year = {2010}, abstract = {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.}, language = {en} } @article{HerzogSchickGaaletal.2012, author = {Herzog, Marc and Schick, Daniel and Gaal, P. and Shayduk, Roman and von Korff Schmising, Clemens and Bargheer, Matias}, title = {Analysis of ultrafast X-ray diffraction data in a linear-chain model of the lattice dynamics}, series = {Applied physics : A, Materials science \& processing}, volume = {106}, journal = {Applied physics : A, Materials science \& processing}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-011-6719-z}, pages = {489 -- 499}, year = {2012}, abstract = {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.}, language = {en} } @article{HerzogSchickLeitenbergeretal.2012, author = {Herzog, Marc and Schick, Daniel and Leitenberger, Wolfram and Shayduk, Roman and van der Veen, Renske M. and Milne, Christopher J. and Johnson, Steven Lee and Vrejoiu, Ionela and Bargheer, Matias}, title = {Tailoring interference and nonlinear manipulation of femtosecond x-rays}, series = {New journal of physics : the open-access journal for physics}, volume = {14}, journal = {New journal of physics : the open-access journal for physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/14/1/013004}, pages = {9}, year = {2012}, abstract = {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.}, language = {en} } @article{NavirianHerzogGoldshteynetal.2011, author = {Navirian, Hengameh A. and Herzog, Marc and Goldshteyn, J. and Leitenberger, Wolfram and Vrejoiu, Ionella and Khakhulin, D. and Wulff, M. and Shayduk, Roman and Gaal, P. and Bargheer, Matias}, title = {Shortening x-ray pulses for pump-probe experiments at synchrotrons}, series = {Journal of applied physics}, volume = {109}, journal = {Journal of applied physics}, number = {12}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-8979}, doi = {10.1063/1.3601057}, pages = {3}, year = {2011}, abstract = {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.}, language = {en} } @article{NavirianSchickGaaletal.2014, author = {Navirian, Hengameh A. and Schick, Daniel and Gaal, Peter and Leitenberger, Wolfram and Shayduk, Roman and Bargheer, Matias}, title = {Thermoelastic study of nanolayered structures using time-resolved X-ray diffraction at high repetition rate}, series = {Applied physics letters}, volume = {104}, journal = {Applied physics letters}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.4861873}, pages = {4}, year = {2014}, abstract = {We investigate the thermoelastic response of a nanolayered sample composed of a metallic SrRuO3 electrode sandwiched between a ferroelectric Pb(Zr0.2Ti0.8)O-3 film with negative thermal expansion and a SrTiO3 substrate. SrRuO3 is rapidly heated by fs-laser pulses with 208 kHz repetition rate. Diffraction of X-ray pulses derived from a synchrotron measures the transient out-of-plane lattice constant c of all three materials simultaneously from 120 ps to 5 mu s with a relative accuracy up to Delta c/c = 10(-6). The in-plane propagation of sound is essential for understanding the delayed out-of-plane compression of Pb(Zr0.2Ti0.8)O-3.}, language = {en} } @article{SchickBojahrHerzogetal.2014, author = {Schick, Daniel and Bojahr, Andre and Herzog, Marc and Shayduk, Roman and von Korff Schmising, Clemens and Bargheer, Matias}, title = {Udkm1Dsim-A simulation toolkit for 1D ultrafast dynamics in condensed matter}, series = {Computer physics communications : an international journal devoted to computational physics and computer programs in physics}, volume = {185}, journal = {Computer physics communications : an international journal devoted to computational physics and computer programs in physics}, number = {2}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0010-4655}, doi = {10.1016/j.cpc.2013.10.009}, pages = {651 -- 660}, year = {2014}, abstract = {The UDKM1DSIM toolbox is a collection of MATLAB (MathWorks Inc.) classes and routines to simulate the structural dynamics and the according X-ray diffraction response in one-dimensional crystalline sample structures upon an arbitrary time-dependent external stimulus, e.g. an ultrashort laser pulse. The toolbox provides the capabilities to define arbitrary layered structures on the atomic level including a rich database of corresponding element-specific physical properties. The excitation of ultrafast dynamics is represented by an N-temperature model which is commonly applied for ultrafast optical excitations. Structural dynamics due to thermal stress are calculated by a linear-chain model of masses and springs. The resulting X-ray diffraction response is computed by dynamical X-ray theory. The UDKM1DSIM toolbox is highly modular and allows for introducing user-defined results at any step in the simulation procedure. Program summary Program title: udkm1Dsim Catalogue identifier: AERH_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AERH_v1_0.html Licensing provisions: BSD No. of lines in distributed program, including test data, etc.: 130221 No. of bytes in distributed program, including test data, etc.: 2746036 Distribution format: tar.gz Programming language: Matlab (MathWorks Inc.). Computer: PC/Workstation. Operating system: Running Matlab installation required (tested on MS Win XP -7, Ubuntu Linux 11.04-13.04). Has the code been vectorized or parallelized?: Parallelization for dynamical XRD computations. Number of processors used: 1-12 for Matlab Parallel Computing Toolbox; 1 - infinity for Matlab Distributed Computing Toolbox External routines: Optional: Matlab Parallel Computing Toolbox, Matlab Distributed Computing Toolbox Required (included in the package): mtimesx Fast Matrix Multiply for Matlab by James Tursa, xml io tools by Jaroslaw Tuszynski, textprogressbar by Paul Proteus Nature of problem: Simulate the lattice dynamics of 1D crystalline sample structures due to an ultrafast excitation including thermal transport and compute the corresponding transient X-ray diffraction pattern. Solution method: Restrictions: The program is restricted to 1D sample structures and is further limited to longitudinal acoustic phonon modes and symmetrical X-ray diffraction geometries. Unusual features: The program is highly modular and allows the inclusion of user-defined inputs at any time of the simulation procedure. Running time: The running time is highly dependent on the number of unit cells in the sample structure and other simulation parameters such as time span or angular grid for X-ray diffraction computations. However, the example files are computed in approx. 1-5 min each on a 8 Core Processor with 16 GB RAM available.}, language = {en} } @article{SchickBojahrHerzogetal.2012, author = {Schick, Daniel and Bojahr, Andre and Herzog, Marc and von Korff Schmising, Clemens and Shayduk, Roman and Leitenberger, Wolfram and Gaa, P. and Bargheer, Matias}, title = {Normalization schemes for ultrafast x-ray diffraction using a table-top laser-driven plasma source}, series = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, volume = {83}, journal = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0034-6748}, doi = {10.1063/1.3681254}, pages = {7}, year = {2012}, abstract = {We present an experimental setup of a laser-driven x-ray plasma source for femtosecond x-ray diffraction. Different normalization schemes accounting for x-ray source intensity fluctuations are discussed in detail. We apply these schemes to measure the temporal evolution of Bragg peak intensities of perovskite superlattices after ultrafast laser excitation.}, language = {en} }