R -matrix-with-time-dependence theory for ultrafast atomic processes in arbitrary light fields

Abstract

We describe an ab initio and non-perturbative R-matrix with time-dependence theory for ultrafast atomic processes in light fields of arbitrary polarization. The theory is applicable to complex, multielectron atoms and atomic ions subject to ultrashort (particularly few-femtosecond and attosecond) laser pulses with any given ellipticity, and generalizes previous time-dependent R-matrix techniques restricted to linearly polarized fields. We discuss both the fundamental equations, required to propagate the multielectron wavefunction in time, as well as the computational developments necessary for their efficient numerical solution. To verify the accuracy of our approach, we investigate the two-photon ionization of He, irradiated by a pair of time-delayed, circularly polarized, femtosecond laser pulses, and compare photoelectron momentum distributions, in the polarization plane, with those obtained from recent time-dependent close-coupling calculations. The predictive capabilities of our approach are further demonstrated through a study of single-photon detachment from F − in a circularly polarized, femtosecond laser pulse, where the relative contribution of the co-and counter-rotating 2p electrons is quantified. arXiv:1812.00234v1 [physics.atom-ph] 1 Dec 2018

RMT: R-matrix with time-dependence. Solving the semi-relativistic, time-dependent Schrödinger equation for general, multielectron atoms and molecules in intense, ultrashort, arbitrarily polarized laser pulses

“…More recently, it has been found that photoelectron momentum distributions arising from such pulses carry novel signatures of wave-particle duality. Indeed, as predicted theoretically [41,54], and demonstrated experimentally [55,56], the distributions typically contain multi-armed spirals, caused by the interference between outgoing electron wavepackets with different magnetic quantum numbers. Here we investigate the response of a truly multielectron target, Ar, to counter-rotating circularly polarized pulses.…”

Modeling tomographic measurements of photoelectron vortices in counter-rotating circularly polarized laser pulses

“…Further calculations (not shown) demonstrate that an asymmetry is not apparent in the distribution until the time delay is reduced to around 30 fs, which is well outside the error estimate of the measured delay. This asymmetry induced by ionization pathways involving both pulses is well known, and has been observed and analyzed in previous work [30,52].…”

“…RMT has been used to analyze the strong-field dynamics of a variety of atoms and ions, particularly in HHG by noble-gas atoms at near-IR wavelengths [54], strong-field rescattering in F − [55], as well as extreme-ultraviolet-initiated HHG in Ne [56] and Ar + [57]. Recently, RMT calculations of photoelectron momentum distributions for two-photon ionization of helium using counter-rotating circularly polarized pulses [52] were compared against those from time-dependent close-coupling calculations [30]. A further study addressed the influence of the bound-electron magnetic quantum number on detachment yields from F − in circularly polarized pulses [58].…”

Electron correlation and short-range dynamics in attosecond angular streaking

“…In this work, we employ the R-matrix with timedependence (RMT) method [24][25][26][27] to study angular streaking from F − . RMT is an ab initio method that solves the time-dependent Schrödinger equation for multielectron atoms, ions and molecules in strong laser fields.…”

“…Our treatment of the F − ionic structure is described in previous work [26,28,29], and is based on earlier Rmatrix Floquet calculations for this system [30,31]. To investigate electron correlation in the core, we consider two atomic structure models, one in which the residual F atom is treated at the Hartree-Fock level of detail [32], and another that uses pseudo-orbitals to construct a set of configurations for subsequent use in a configurationinteraction calculation of the 1s 2 2s 2 2p 5 2 P o state of F. We couple a single electron to the residual neutral, retaining all 1s 2 2s 2 2p 5 l channels up to l = L max + 1.…”