Core-level nonlinear spectroscopy triggered by stochastic X-ray pulses

Abstract

Stochastic processes are highly relevant in research fields as different as neuroscience, economy, ecology, chemistry, and fundamental physics. However, due to their intrinsic unpredictability, stochastic mechanisms are very challenging for any kind of investigations and practical applications. Here we report the deliberate use of stochastic X-ray pulses in two-dimensional spectroscopy to the simultaneous mapping of unoccupied and occupied electronic states of atoms in a regime where the opacity and transparency properties of matter are subject to the incident intensity and photon energy. A readily transferable matrix formalism is presented to extract the electronic states from a dataset measured with the monitored input from a stochastic excitation source. The presented formalism enables investigations of the response of the electronic structure to irradiation with intense X-ray pulses while the time structure of the incident pulses is preserved.

Resonant X-ray Emission Spectroscopy with a SASE Beam

“…In this work, we further investigated the possibility to perform simultaneous X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) measurement at XFELs with the stochastic SASE beam. The described methodology allows obtaining the combined XAS and XES data in the form of an RXES plane reconstructed from the measured incident SASE and X-ray emission spectra [10]. Conventional XAS spectrum or RXES plane acquisition involves special treatment of the incident X-ray beam, e.g., monochromatization [19], beam splitting [20], or seeding [21], which reduces the XFEL beam intensity on the sample or extends the XFEL pulse duration [22].…”

“…The RXES planes reconstruction is based on a matrix formalism, where for the number of SASE pulses k, the set of the measured emission spectra S kn , with n denoting the number of points in a single emission spectrum, is described with the following matrix equation [10]:…”

“…Over the past few years, many developments have been made to overcome these limitations and take full advantage of the random nature of the XFEL pulses. One recently introduced approach is based on the reconstruction methodology that allows following electronic transitions with a temporal resolution solely restricted to the incident pulse duration [10]. It has been shown that the combination of the stochastic nature of SASE pulses Appl.…”

“…In the present work, we evaluated the influence of the number of XFEL shots recorded on the quality of the RXES planes reconstructed with the previously reported algorithm [10]. The presented analysis facilitates planning an RXES experiment under SASE conditions at XFELs.…”

XABOOM: An X-Ray Absorption Benchmark of Organic Molecules Based on Carbon, Nitrogen, and Oxygen 1s → π ∗ Transitions

“…In recent times, the field of X-ray spectroscopy has progressed rapidly as a result of the development and construction of modern synchrotrons and X-ray free-electron lasers (XFELs), enabling the investigation of light-matter interactions at unprecedented time-resolution and radiation intensity. 1,2 These installations facilitate the study of exotic molecular properties and provide a sensitive experimental tool to questions such as (i) probing chemical reactions in real time, as exemplified by the tracking of the photocatalytic cycle in photosynthesis, [2][3][4][5][6] (ii) considering the structure of molecular samples, such as the local structure of liquid water, [7][8][9] (iii) identifying the oxidation state of transition metals in organometallic complexes, with examples including the Fe/Mo atoms in nitrogenase, [10][11][12] (iv) investigating non-linear properties, such as stimulated emission and two-photon absorption, [13][14][15][16][17] and more. By use of pump-probe protocols, time-resolved spectroscopies can study a multitude of dynamical processes, but this potential is yet to be fully explored due to the significant theoretical and experimental difficulties of performing such studies, with, for instance, experimental facilities only being made available during the last decade.…”