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  - Pontius, Niko
A1  - Beye, Martin
A1  - Trabant, Christoph
A1  - Mitzner, Rolf
A1  - Sorgenfrei, Nomi
A1  - Kachel, Torsten
A1  - Woestmann, Michael
A1  - Roling, Sebastian
A1  - Zacharias, Helmut
A1  - Ivanov, Rosen
A1  - Treusch, Rolf
A1  - Buchholz, Marcel
A1  - Metcalf, Pete
A1  - Schuessler-Langeheine, Christian
A1  - Föhlisch, Alexander
T1  - Probing the non-equilibrium transient state in magnetite by a jitter-free two-color X-ray pump and X-ray probe experiment
JF  - Structural dynamics
N2  - We present a general experimental concept for jitter-free pump and probe experiments at free electron lasers. By generating pump and probe pulse from one and the same X-ray pulse using an optical split-and-delay unit, we obtain a temporal resolution that is limited only by the X-ray pulse lengths. In a two-color X-ray pump and X-ray probe experiment with sub 70 fs temporal resolution, we selectively probe the response of orbital and charge degree of freedom in the prototypical functional oxide magnetite after photoexcitation. We find electronic order to be quenched on a time scale of (30 +/- 30) fs and hence most likely faster than what is to be expected for any lattice dynamics. Our experimental result hints to the formation of a short lived transient state with decoupled electronic and lattice degree of freedom in magnetite. The excitation and relaxation mechanism for X-ray pumping is discussed within a simple model leading to the conclusion that within the first 10 fs the original photoexcitation decays into low-energy electronic excitations comparable to what is achieved by optical pump pulse excitation. Our findings show on which time scales dynamical decoupling of degrees of freedom in functional oxides can be expected and how to probe this selectively with soft X-ray pulses. Results can be expected to provide crucial information for theories for ultrafast behavior of materials and help to develop concepts for novel switching devices. (C) 2018 Author(s).
Y1  - 2018
U6  - https://doi.org/10.1063/1.5042847
SN  - 2329-7778
VL  - 5
IS  - 5
PB  - American Institute of Physics
CY  - Melville
ER  -