Analysis of the halo background in femtosecond slicing experiments

J Synchrotron Radiat. 2016 May;23(Pt 3):700-11. doi: 10.1107/S160057751600401X. Epub 2016 Apr 14.

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.

Keywords: X-ray scattering; XMCD; femtosecond slicing; halo; pump–probe.

Publication types

  • Research Support, Non-U.S. Gov't