Proposal of X-ray absorption spectroscopy and magnetic circular dichroism using broadband free-electron lasers

Abstract

X‐ray free‐electron lasers (XFELs) have been widely used for applications such as X‐ray crystallography and magnetic spin probes because of their unprecedented performance. Recently, time‐resolved X‐ray magnetic circular dichroism (XMCD) with ultrafast XFEL pulses have made it possible to achieve an instantaneous view of atomic de‐excitation. However, owing to the narrow bandwidth and coherence of XFELs, X‐ray absorption spectroscopy (XAS) and XMCD are time‐ and effort‐consuming for both machine scientists and users of XFELs. In this work, an efficient scheme using a broadband XFEL pulse and single‐shot X‐ray spectrometer is proposed, in which the XAS and XMCD measurements can be accomplished with the same machine conditions. An evolutionary multi‐objective optimization algorithm is used to maximize the XFEL bandwidth offered by the Shanghai Soft X‐ray FEL user facility without additional hardware. A numerical example using MnO is demonstrated, showing that, by using approximately 1000 consecutive XFEL shots with a central photon energy of 650 eV and full bandwidth of 4.4%, precise spectral measurements for XAS and XMCD can be achieved. Additional considerations related to single‐shot XAS and XMCD are discussed.

Proposal of a non-invasive spectrum diagnostic instrumentation for hard X-rays with high repetitions

“…In our previous work, two methods were demonstrated numerically for TOF spectrum deconvolution. One was based on the Wiener filter in the frequency domain [24] and the other is based on the least squares constrained linear regression in the time domain [19]. In this work, a Wiener filter is sufficient for TOF spectrum deconvolution because of its robustness and the capability of parallel computing.…”

Polarization control of an x-ray free electron laser oscillator

“…Linear Coherent Light Source (LCLS) first produced hard X-ray FEL in 2009, after that several XFELs [1][2][3][4][5] have been constructed world widely. In recent years, a large mount of complicated schemes have been developed in pursuit of, e.g., full coherence [6,7], multi-color operation [8,9], ultra-fast operation [10,11], and large bandwidth operation [12,13], tunable polarization operation [14,15].…”