TY  - JOUR
A1  - Schick, Daniel
A1  - Le Guyader, Loic
A1  - Pontius, Niko
A1  - Radu, Ilie
A1  - Kachel, Torsten
A1  - Mitzner, Rolf
A1  - Zeschke, Thomas
A1  - Schuessler-Langeheine, Christian
A1  - Föhlisch, Alexander
A1  - Holldack, Karsten
T1  - Analysis of the halo background in femtosecond slicing experiments
JF  - Journal of synchrotron radiation
N2  - 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.
KW  - femtosecond slicing
KW  - halo
KW  - pump-probe
KW  - XMCD
KW  - X-ray scattering
Y1  - 2016
U6  - https://doi.org/10.1107/S160057751600401X
SN  - 1600-5775
VL  - 23
SP  - 700
EP  - 711
PB  - International Union of Crystallography
CY  - Chester
ER  - 
TY  - JOUR
A1  - Klinkusch, Stefan
A1  - Klamroth, Tillmann
T1  - 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
JF  - Journal of theoretical and computational chemistry
N2  - 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.
KW  - Electron dynamics
KW  - time-dependent configuration interaction
KW  - pump-probe
Y1  - 2013
U6  - https://doi.org/10.1142/S0219633613500053
SN  - 0219-6336
VL  - 12
IS  - 3
PB  - World Scientific
CY  - Singapore
ER  - 
TY  - JOUR
A1  - Kühn, Danilo
A1  - Giangrisostomi, Erika
A1  - Jay, Raphael Martin
A1  - Sorgenfrei, Florian
A1  - Föhlisch, Alexander
T1  - The influence of x-ray pulse length on space-charge effects in optical pump/x-ray probe photoemission
JF  - New journal of physics : the open-access journal for physics
N2  - 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.
KW  - space-charge effects
KW  - mean-field model
KW  - x-ray photoemission
KW  - electron spectroscopy
KW  - pump-probe
KW  - ARTOF
Y1  - 2019
U6  - https://doi.org/10.1088/1367-2630/ab2f5c
SN  - 1367-2630
VL  - 21
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -