@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{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{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}
}
@misc{PavlenkoSanderMitzscherlingetal.2016,
  author    = {Pavlenko, Elena S. and Sander, Mathias and Mitzscherling, Steffen and Pudell, Jan-Etienne and Zamponi, Flavio and R{\"o}ssle, Matthias and Bojahr, Andre and Bargheer, Matias},
  title     = {Azobenzene - functionalized polyelectrolyte nanolayers as ultrafast optoacoustic transducers},
  volume    = {8},
  doi       = {10.1039/C6NR01448H},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-101996},
  pages     = {13297 -- 13302},
  year      = {2016},
  abstract  = {We introduce azobenzene-functionalized polyelectrolyte multilayers as efficient, inexpensive optoacoustic transducers for hyper-sound strain waves in the GHz range. By picosecond transient reflectivity measurements we study the creation of nanoscale strain waves, their reflection from interfaces, damping by scattering from nanoparticles and propagation in soft and hard adjacent materials like polymer layers, quartz and mica. The amplitude of the generated strain ε ∼ 5 × 10-4 is calibrated by ultrafast X-ray diffraction.},
  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{MaertenBojahrGohlkeetal.2015,
  author    = {Maerten, Lena and Bojahr, Andre and Gohlke, Mathias and R{\"o}ssle, Matthias and Bargheer, Matias},
  title     = {Coupling of GHz Phonons to Ferroelastic Domain Walls in SrTiO3},
  series = {Physical review letters},
  volume    = {114},
  journal   = {Physical review letters},
  number    = {4},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {0031-9007},
  doi       = {10.1103/PhysRevLett.114.047401},
  pages     = {5},
  year      = {2015},
  abstract  = {We study the linear and nonlinear acoustic response of SrTiO3 across its ferroelastic transition at T-a = 105 K by time domain Brillouin scattering. Above T-a we observe that for a strain amplitude of similar to 0.18\% the sound velocity for compressive strain exceeds the tensile strain velocity by 3\%. Below T-a we find a giant slowing down of the sound velocity by 12\% and attribute this to the coupling of GHz phonons to ferroelastic twin domain walls. We propose a new mechanism for this coupling on the ultrafast time scale, providing an important new test ground for theories used to simulate atomic motion in domain forming crystals.},
  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{SchickHerzogBojahretal.2014,
  author    = {Schick, Daniel and Herzog, Marc and Bojahr, Andre and Leitenberger, Wolfram and Hertwig, Andreas and Shayduk, Roman and Bargheer, Matias},
  title     = {Ultrafast lattice response of photoexcited thin films studied by X-ray diffraction},
  series = {Structural dynamics},
  volume    = {1},
  journal   = {Structural dynamics},
  number    = {6},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {2329-7778},
  doi       = {10.1063/1.4901228},
  pages     = {13},
  year      = {2014},
  abstract  = {Using ultrafast X-ray diffraction, we study the coherent picosecond lattice dynamics of photoexcited thin films in the two limiting cases, where the photoinduced stress profile decays on a length scale larger and smaller than the film thickness. We solve a unifying analytical model of the strain propagation for acoustic impedance-matched opaque films on a semi-infinite transparent substrate, showing that the lattice dynamics essentially depend on two parameters: One for the spatial profile and one for the amplitude of the strain. We illustrate the results by comparison with high-quality ultrafast X-ray diffraction data of SrRuO3 films on SrTiO3 substrates. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.},
  language  = {en}
}
@article{PavlenkoSanderMitzscherlingetal.2016,
  author    = {Pavlenko, Elena S. and Sander, Mathias and Mitzscherling, S. and Pudell, Jan-Etienne and Zamponi, Flavio and Roessle, M. and Bojahr, Andre and Bargheer, Matias},
  title     = {Azobenzene - functionalized polyelectrolyte nanolayers as ultrafast optoacoustic transducers},
  series = {Nanoscale},
  volume    = {8},
  journal   = {Nanoscale},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2040-3364},
  doi       = {10.1039/c6nr01448h},
  pages     = {13297 -- 13302},
  year      = {2016},
  abstract  = {We introduce azobenzene-functionalized polyelectrolyte multilayers as efficient, inexpensive optoacoustic transducers for hyper-sound strain waves in the GHz range. By picosecond transient reflectivity measurements we study the creation of nanoscale strain waves, their reflection from interfaces, damping by scattering from nanoparticles and propagation in soft and hard adjacent materials like polymer layers, quartz and mica. The amplitude of the generated strain epsilon similar to 5 x 10(-4) is calibrated by ultrafast X-ray diffraction.},
  language  = {en}
}