Imaging instantaneous electron flow with ultrafast resonant x-ray scattering

Abstract

We propose a way to image dynamical properties of nonstationary electron systems using ultrafast resonant x-ray scattering. Employing a rigorous theoretical analysis within the framework of quantum electrodynamics, we demonstrate that a single scattering pattern from a nonstationary electron system encodes the instantaneous interatomic electron current in addition to the structural information usually obtained by resonant x-ray scattering from stationary systems. Thus, inelastic contributions that are indistinguishable from elastic processes induced by a broadband probe pulse, instead of being a concern, serve as an advantage for time-resolved resonant x-ray scattering. Thereby, we propose an approach combining elastic and inelastic resonant x-ray scattering for imaging dynamics of nonstationary electron systems in both real space and real time. In order to illustrate its power, we show how it can be applied to image the electron-hole current in an ionized diatomic molecule.

Imaging electron dynamics with time- and angle-resolved photoelectron spectroscopy

“…Therefore, angle-resolved photoelectron spectra do not follow the time evolution of the electron density. A similar effect that a measured signal from an electronic wave packet does not follow the time-dependent electron density has been shown for time-resolved resonant [23,24] and nonresonant [21] x-ray scattering patterns as well as time-resolved electron diffraction patterns [40].…”

“…Alternatively to ultrafast resonant x-ray scattering [23,24], one can use time-and angle-resolved photoelectron spectroscopy to obtain real-space information on instantaneous charge distributions and electron currents in molecules. Recent progress in attosecond science makes an experimental implementation of this technique feasible in the near future [14].…”

“…In these studies, the effect of the broad bandwidth of an ultrashort probe pulse has either been neglected [17,18,20] or approximated [19]. However, we have earlier demonstrated that an accurate treatment within the quantum electrodynamics (QED) approach taking into account all transitions that can be induced by a broadband probe pulse is necessary for a correct description of ultrafast x-ray scattering from a nonstationary electronic system [21][22][23][24]. Therefore, since this should also be true for time-resolved photoelectron imaging, we apply the QED treatment to describe the interaction of a nonstationary electronic system with an ultrashort isolated probe pulse inducing single-photon ionization.…”

“…We describe the interaction between the electronic system and the photoionizing ultrashort probe pulse using a similar formalism to the one applied for the study of ultrafast x-ray scattering [21][22][23][24]. Since we assume that the probe pulse does not temporally overlap with the pump pulse, the interaction of the electronic system with the probe pulse can be considered independently from the pump pulse [25].…”

Correlation-driven charge migration following double ionization and attosecond transient absorption spectroscopy

“…Among those techniques which have been proposed for monitoring ultrafast electron dynamics [11][12][13][14][15][16], ATAS [7,[17][18][19] stands out since it combines high spectral and high temporal resolution. So far, it has already been successfully applied to the electron dynamics in atoms [7,17,[20][21][22][23] as well as to the dynamics in solid state systems [24,25].…”