@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{SchickBojahrHerzogetal.2013, author = {Schick, Daniel and Bojahr, Andre and Herzog, Marc and Gaal, P. and Vrejoiu, I. and Bargheer, Matias}, title = {Following Strain-Induced Mosaicity Changes of Ferroelectric Thin Films by Ultrafast Reciprocal Space Mapping}, series = {Physical review letters}, volume = {110}, journal = {Physical review letters}, number = {9}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.110.095502}, pages = {5}, year = {2013}, abstract = {We investigate coherent phonon propagation in a thin film of ferroelectric PbZr0.2Ti0.8O3 (PZT) by ultrafast x-ray diffraction experiments, which are analyzed as time-resolved reciprocal space mapping in order to observe the in-and out-of-plane structural dynamics, simultaneously. The mosaic structure of the PZT leads to a coupling of the excited out-of-plane expansion to in-plane lattice dynamics on a picosecond time scale, which is not observed for out-of-plane compression.}, language = {en} } @article{ShaydukHerzogBojahretal.2013, author = {Shayduk, Roman and Herzog, Marc and Bojahr, Andre and Schick, Daniel and Gaal, Peter and Leitenberger, Wolfram and Navirian, Hengameh and Sander, Mathias and Goldshteyn, Jevgenij and Vrejoiu, Ionela and Bargheer, Matias}, title = {Direct time-domain sampling of subterahertz coherent acoustic phonon spectra in SrTiO3 using ultrafast x-ray diffraction}, series = {Physical review : B, Condensed matter and materials physics}, volume = {87}, journal = {Physical review : B, Condensed matter and materials physics}, number = {18}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.87.184301}, pages = {7}, year = {2013}, abstract = {We synthesize sub-THz longitudinal quasimonochromatic acoustic phonons in a SrTiO3 single crystal using a SrRuO3/SrTiO3 superlattice as an optical-acoustic transducer. The generated acoustic phonon spectrum is determined using ultrafast x-ray diffraction. The analysis of the generated phonon spectrum in the time domain reveals a k-vector dependent phonon lifetime. It is observed that even at sub-THz frequencies the phonon lifetime agrees with the 1/omega(2) power law known from Akhiezer's model for hyper sound attenuation. The observed shift of the synthesized spectrum to the higher q is discussed in the framework of nonlinear effects appearing due to the high amplitude of the synthesized phonons.}, language = {en} } @article{BojahrHerzogMitzscherlingetal.2013, author = {Bojahr, Andre and Herzog, Marc and Mitzscherling, Steffen and Maerten, Lena and Schick, Daniel and Goldshteyn, J. and Leitenberger, Wolfram and Shayduk, R. and Gaal, P. and Bargheer, Matias}, title = {Brillouin scattering of visible and hard X-ray photons from optically synthesized phonon wavepackets}, series = {Optics express : the international electronic journal of optics}, volume = {21}, journal = {Optics express : the international electronic journal of optics}, number = {18}, publisher = {Optical Society of America}, address = {Washington}, issn = {1094-4087}, doi = {10.1364/OE.21.021188}, pages = {21188 -- 21197}, year = {2013}, abstract = {We monitor how destructive interference of undesired phonon frequency components shapes a quasi-monochromatic hypersound wavepacket spectrum during its local real-time preparation by a nanometric transducer and follow the subsequent decay by nonlinear coupling. We prove each frequency component of an optical supercontinuum probe to be sensitive to one particular phonon wavevector in bulk material and cross-check this by ultrafast x-ray diffraction experiments with direct access to the lattice dynamics. Establishing reliable experimental techniques with direct access to the transient spectrum of the excitation is crucial for the interpretation in strongly nonlinear regimes, such as soliton formation.}, language = {en} } @article{SchickShaydukBojahretal.2013, author = {Schick, Daniel and Shayduk, Roman and Bojahr, Andre and Herzog, Marc and von Korff Schmising, Clemens and Gaal, Peter and Bargheer, Matias}, title = {Ultrafast reciprocal-space mapping with a convergent beam}, series = {JOURNAL OF APPLIED CRYSTALLOGRAPHY}, volume = {46}, journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY}, number = {10}, publisher = {WILEY-BLACKWELL}, address = {HOBOKEN}, issn = {0021-8898}, doi = {10.1107/S0021889813020013}, pages = {1372 -- 1377}, year = {2013}, abstract = {A diffractometer setup is presented, based on a laser-driven plasma X-ray source for reciprocal-space mapping with femtosecond temporal resolution. In order to map out the reciprocal space, an X-ray optic with a convergent beam is used with an X-ray area detector to detect symmetrically and asymmetrically diffracted X-ray photons simultaneously. The setup is particularly suited for measuring thin films or imperfect bulk samples with broad rocking curves. For quasi-perfect crystalline samples with insignificant in-plane Bragg peak broadening, the measured reciprocal-space maps can be corrected for the known resolution function of the diffractometer in order to achieve high-resolution rocking curves with improved data quality. In this case, the resolution of the diffractometer is not limited by the convergence of the incoming X-ray beam but is solely determined by its energy bandwidth.}, 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{EnquistNavirianNueskeetal.2010, author = {Enquist, Henrik and Navirian, Hengameh and Nueske, Ralf and von Korff Schmising, Clemens and Jurgilaitis, Andrius and Herzog, Marc and Bargheer, Matias and Sondhauss, Peter and Larsson, Joergen}, title = {Subpicosecond hard x-ray streak camera using single-photon counting}, issn = {0146-9592}, doi = {10.1364/OL.35.003219}, year = {2010}, abstract = {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.}, language = {en} } @phdthesis{Herzog2012, author = {Herzog, Marc}, title = {Structural dynamics of photoexcited nanolayered perovskites studied by ultrafast x-ray diffraction}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-62632}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {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.}, language = {en} }