@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{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{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{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{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}
}
@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{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{BojahrHerzogSchicketal.2012,
  author    = {Bojahr, Andre and Herzog, Marc and Schick, Daniel and Vrejoiu, Ionela and Bargheer, Matias},
  title     = {Calibrated real-time detection of nonlinearly propagating strain waves},
  series = {Physical review : B, Condensed matter and materials physics},
  volume    = {86},
  journal   = {Physical review : B, Condensed matter and materials physics},
  number    = {14},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {1098-0121},
  doi       = {10.1103/PhysRevB.86.144306},
  pages     = {5},
  year      = {2012},
  abstract  = {Epitaxially grown metallic oxide transducers support the generation of ultrashort strain pulses in SrTiO3 (STO) with high amplitudes up to 0.5\%. The strain amplitudes are calibrated by real-time measurements of the lattice deformation using ultrafast x-ray diffraction. We determine the speed at which the strain fronts propagate by broadband picosecond ultrasonics and conclude that, above a strain level of approx. 0.2\%, the compressive and tensile strain components travel at considerably different sound velocities, indicating nonlinear wave behavior. Simulations based on an anharmonic linear-chain model are in excellent accord with the experimental findings and show how the spectrum of coherent phonon modes changes with time.},
  language  = {en}
}
@article{BojahrSchickMaertenetal.2012,
  author    = {Bojahr, Andre and Schick, Daniel and M{\"a}rten, Lena and Herzog, Marc and Vrejoiu, Ionela and von Korff Schmising, Clemens and Milne, Chris and Johnson, Steven Lee and Bargheer, Matias},
  title     = {Comparing the oscillation phase in optical pump-probe spectra to ultrafast x-ray diffraction in the metal-dielectric SrRuO3/SrTiO3 superlattice},
  series = {Physical review : B, Condensed matter and materials physics},
  volume    = {85},
  journal   = {Physical review : B, Condensed matter and materials physics},
  number    = {22},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {1098-0121},
  doi       = {10.1103/PhysRevB.85.224302},
  pages     = {6},
  year      = {2012},
  abstract  = {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.},
  language  = {en}
}