@article{KuehnGiangrisostomiJayetal.2019,
  author    = {K{\"u}hn, Danilo and Giangrisostomi, Erika and Jay, Raphael Martin and Sorgenfrei, Florian and F{\"o}hlisch, Alexander},
  title     = {The influence of x-ray pulse length on space-charge effects in optical pump/x-ray probe photoemission},
  series = {New journal of physics : the open-access journal for physics},
  volume    = {21},
  journal   = {New journal of physics : the open-access journal for physics},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {1367-2630},
  doi       = {10.1088/1367-2630/ab2f5c},
  pages     = {12},
  year      = {2019},
  abstract  = {Pump-probe photoelectron spectroscopy (PES) is a versatile tool to investigate the dynamics of transient states of excited matter. Vacuum space-charge effects can mask these dynamics and complicate the interpretation of electron spectra. Here we report on space-charge effects in Au 4f photoemission from a polycrystalline gold surface, excited with moderately intense 90 ps (FWHM) soft x-ray probe pulses, under the influence of the Coulomb forces exerted by a pump electron cloud, which was produced by intense 40 fs laser pulses. The experimentally observed kinetic energy shift and spectral broadening of the Au 4f lines, measured with highly-efficient time-of-flight spectroscopy, are in good agreement with simulations utilizing a mean-field model of the electrostatic pump electron potential. This confirms that the line broadening is predominantly caused by variations in the take-off time of the probe electrons without appreciable influence of local scattering events. Our findings might be of general interest for pump-probe PES with picosecond-pulse-length sources.},
  language  = {en}
}
@article{KlinkuschKlamroth2013,
  author    = {Klinkusch, Stefan and Klamroth, Tillmann},
  title     = {Simulations of pump-probe exitations of electronic wave packets for a large qusi-rigid molecular system by means of an extension to the time-dependent configuration interaction singles method},
  series = {Journal of theoretical and computational chemistry},
  volume    = {12},
  journal   = {Journal of theoretical and computational chemistry},
  number    = {3},
  publisher = {World Scientific},
  address   = {Singapore},
  issn      = {0219-6336},
  doi       = {10.1142/S0219633613500053},
  pages     = {17},
  year      = {2013},
  abstract  = {In this paper, we report simulations of laser-driven many-electron dynamics by means of the time-dependent configuration interaction singles (TD-CIS) approach. Photoionization is included by a heuristic model within calculations employing standard Gaussian basis sets. Benzo[g]-N-methyl-quinolinium-7-hydroxylate (BMQ7H) serves as a test system to generate predefined wave packets, i.e. a superposition between the ground and fifth excited state, in a large molecule. For this molecule, these two states have a very similar geometry, which enables us to use the fixed nuclei approximation. Furthermore, this geometric stability would also prevent a dephasing of the electron wave packet due to nuclear dynamics in an experimental realization of our simulations. We also simulate the possible detection of such a wave packet by ultra short probe laser pulses, i.e. pump-probe spectra.},
  language  = {en}
}
@article{SchickLeGuyaderPontiusetal.2016,
  author    = {Schick, Daniel and Le Guyader, Loic and Pontius, Niko and Radu, Ilie and Kachel, Torsten and Mitzner, Rolf and Zeschke, Thomas and Schuessler-Langeheine, Christian and F{\"o}hlisch, Alexander and Holldack, Karsten},
  title     = {Analysis of the halo background in femtosecond slicing experiments},
  series = {Journal of synchrotron radiation},
  volume    = {23},
  journal   = {Journal of synchrotron radiation},
  publisher = {International Union of Crystallography},
  address   = {Chester},
  issn      = {1600-5775},
  doi       = {10.1107/S160057751600401X},
  pages     = {700 -- 711},
  year      = {2016},
  abstract  = {The slicing facility FemtoSpeX at BESSY II offers unique opportunities to study photo-induced dynamics on femtosecond time scales by means of X-ray magnetic circular dichroism, resonant and non-resonant X-ray diffraction, and X-ray absorption spectroscopy experiments in the soft X-ray regime. Besides femtosecond X-ray pulses, slicing sources inherently also produce a so-called `halo' background with a different time structure, polarization and pointing. Here a detailed experimental characterization of the halo radiation is presented, and a method is demonstrated for its correct and unambiguous removal from femtosecond time-resolved data using a special laser triggering scheme as well as analytical models. Examples are given for time-resolved measurements with corresponding halo correction, and errors of the relevant physical quantities caused by either neglecting or by applying a simplified model to describe this background are estimated.},
  language  = {en}
}