Angle-resolved Wigner time delay in atomic photoionization: The 4 d subshell of free and confined Xe
TL;DR: In this paper, the angular dependence of photoemission time delay for the inner $n{d}_{3/2}$ and inner subshells of free and confined Xe is studied in the dipole relativistic random phase approximation.
Abstract: The angular dependence of photoemission time delay for the inner $n{d}_{3/2}$ and $n{d}_{5/2}$ subshells of free and confined Xe is studied in the dipole relativistic random phase approximation. A finite spherical annular well potential is used to model the confinement due to fullerene ${C}_{60}$ cage. Near cancellations in a variety of the dipole amplitudes, Cooper-like minima, are found. The effects of confinement on the angular dependence, primarily confinement resonances, are demonstrated and detailed.
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TL;DR: In this article, the angular-resolved RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) measurements on valence shells of noble-gas atoms (Ne, Ar, Kr, and Xe) are simulated.
Abstract: We simulate angular-resolved RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) measurements on valence shells of noble-gas atoms (Ne, Ar, Kr, and Xe). Our nonperturbative numerical simulation is based on solution of the time-dependent Schr\"odinger equation (TDSE) for a target atom driven by an ionizing XUV and dressing IR fields. From these simulations we extract the angular-dependent magnitude and phase of the RABBITT oscillations and deduce the corresponding angular anisotropy $\ensuremath{\beta}$ parameter and Wigner time delay ${\ensuremath{\tau}}_{W}$ for the single XUV photon absorption that initiates the RABBITT process. Said $\ensuremath{\beta}$ and ${\ensuremath{\tau}}_{W}$ parameters are compared with calculations in the random-phase approximation with exchange (RPAE), which includes intershell correlation. This comparison is used to test various effective potentials employed in the one-electron TDSE. In lighter atoms (Ne and Ar), several effective potentials are found to provide accurate simulations of RABBITT measurements for a wide range of photon energies up to 100 eV above the valence-shell threshold. In heavier atoms (Kr and Xe), the onset of strong correlation with the $d$ shell restricts the validity of the single active electron approximation to several tens of eV above the valence-shell threshold.
43 citations
TL;DR: In this article, the phase difference between two-photon pathways involving absorption and emission of an infrared photon is extracted using two phase-locked Extreme Ultraviolet pulses of frequency ω and 2ω, from a Free-Electron Laser.
Abstract: Quantum mechanically, photoionization can be fully described by the complex photoionization amplitudes that describe the transition between the ground state and the continuum state. Knowledge of the value of the phase of these amplitudes has been a central interest in photoionization studies and newly developing attosecond science, since the phase can reveal important information about phenomena such as electron correlation. We present a new attosecond-precision interferometric method of angle-resolved measurement for the phase of the photoionization amplitudes, using two phase-locked Extreme Ultraviolet pulses of frequency ω and 2ω, from a Free-Electron Laser. Phase differences ∆η̃ between oneand two-photon ionization channels, averaged over multiple wave packets, are extracted for neon 2p electrons as a function of emission angle at photoelectron energies 7.9, 10.2, and 16.6 eV. ∆η̃ is nearly constant for emission parallel to the electric vector but increases at 10.2 eV for emission perpendicular to the electric vector. We model our observations with both perturbation and ab initio theory, and find excellent agreement. In the existing method for attosecond measurement, Reconstruction of Attosecond Beating By Interference of Two-photon Transitions (RABBITT), a phase difference between two-photon pathways involving absorption and emission of an infrared photon is extracted. Our method can be used for extraction of a phase difference between single-photon and two-photon pathways and provides a new tool for attosecond science, which is complementary to RABBITT. ∗ corresponding author; kiyoshi.ueda@tohoku.ac.jp † Now at LIDYL, CEA, CNRS, Université Paris-Saclay, CEA-Saclay, 91191 Gif-sur-Yvette, France. ‡ corresponding author; prince@elettra.eu
28 citations
TL;DR: In this article, the authors studied the dynamics of Xe 4d photoionization on its natural time scale combining attosecond interferometry and coincidence spectroscopy, and identified two interfering ionization mechanisms: the broad giant dipole resonance with a fast decay time less than 50 as, and a narrow resonance at threshold induced by spin-flip transitions, with much longer decay times of several hundred as.
Abstract: The photoionization of xenon atoms in the 70–100 eV range reveals several fascinating physical phenomena such as a giant resonance induced by the dynamic rearrangement of the electron cloud after photon absorption, an anomalous branching ratio between intermediate Xe+ states separated by the spin-orbit interaction and multiple Auger decay processes. These phenomena have been studied in the past, using in particular synchrotron radiation, but without access to real-time dynamics. Here, we study the dynamics of Xe 4d photoionization on its natural time scale combining attosecond interferometry and coincidence spectroscopy. A time-frequency analysis of the involved transitions allows us to identify two interfering ionization mechanisms: the broad giant dipole resonance with a fast decay time less than 50 as, and a narrow resonance at threshold induced by spin-flip transitions, with much longer decay times of several hundred as. Our results provide insight into the complex electron-spin dynamics of photo-induced phenomena.
20 citations
TL;DR: A novel technique of single-shot referencing in the collinear back-focusing geometry has been introduced that enables us to distinguish the signal from principal photoelectron peaks due to ionization by extreme ultraviolet radiation only and infrared-induced sideband contributions, especially in the regions of spectral overlap.
Abstract: Attosecond photoemission delays for all the valence (5p3/2, 5p1/2, 5s, 4d5/2, 4d3/2) subshells of xenon have been accessed using the interferometric RABBITT technique. The 4d subshell delays in Xe have been accessed for the first time, to the best of our knowledge, due to the high photon energy used. A novel technique of single-shot referencing in the collinear back-focusing geometry has been introduced. This enables us to distinguish the signal from principal photoelectron peaks due to ionization by extreme ultraviolet radiation only and infrared-induced sideband contributions, especially in the regions of spectral overlap.
18 citations
TL;DR: In this paper, a review of investigations of the electronic structure and dynamics of atoms encaged in a single molecule is presented, where the major effects of confinement on the dynamical properties, e.g., confinement resonances, hybridization, Wigner time delay, are delineated.
Abstract: Confined atomic systems are of great importance owing a multitude of possible applications in various areas of science and technology. Of particular interest are atoms encaged in the $$\hbox {C}_{{60}}$$
molecule, $$\hbox {A}@\hbox {C}_{{60}}$$
, since the near-spherical symmetry of $$\hbox {C}_{{60}}$$
simplifies theoretical studies, and the stability of $$\hbox {C}_{{60}}$$
renders it amenable to experimental examination. A review of investigations of the electronic structure and dynamics of $$\hbox {A}@\hbox {C}_{{60}}$$
is presented in this manuscript focusing on developments in the last decade. Addressed mainly are how the confinement affects electronic structure properties such as ionization potentials, localization of atomic electrons, Shannon entropy, correlation effects, relativistic interactions, and others. In the area of dynamics, photoionization and e-
$$\hbox {A}@\hbox {C}_{{60}}$$
scattering are reviewed and summarized, and the major effects of confinement on the dynamical properties, e.g., confinement resonances, hybridization, Wigner time delay, are delineated.
15 citations