Schick, D.; Le Guyader, L.; Pontius, N.; Radu, I.; Kachel, T.; Mitzner, R.; Zeschke, T.; Schüssler-Langeheine, C.; Föhlisch, A.; Holldack, K.: Analysis of the halo background in femtosecond slicing experiments. Journal of Synchrotron Radiation 23 (2016), p. 700-711

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.