Atomic harmonic generation in time-dependentR-matrix theory

Abstract

We have developed the capability to determine accurate harmonic spectra for multielectron atoms within time-dependent R-matrix (TDRM) theory. Harmonic spectra can be calculated using the expectation value of the dipole length, velocity or acceleration operator. We assess the calculation of the harmonic spectrum from He irradiated by 390 nm laser light with intensities up to 4 × 10 14 Wcm −2 using each form, including the influence of the multielectron basis used in the TDRM code. The spectra are consistent between the different forms, although the dipole acceleration calculation breaks down at lower harmonics. The results obtained from TDRM theory are compared with results from the HELIUM code finding good quantitative agreement between the methods. We find that bases which include pseudostates give the best comparison with the HELIUM code, but models comprising only physical orbitals also produce accurate results.

Harmonic generation by noble-gas atoms in the near-IR regime usingab initiotime-dependentR-matrix theory

“…The two methods can therefore explore the influence of a different set of interactions on the electron dynamics. Through the inclusion of correlation orbitals, the RMT approach has the capability to obtain an accurate description of the dynamics of open-shell systems as well as closed-shell systems [12,13,18,19]. The capability to account for correlation in both the initial and residual ionic system is critical for this accuracy.…”

“…Previously, we have applied time-dependent R-matrix (TDRM) theory to investigate HHG at a wavelength of 390 nm [12][13][14]. These studies demonstrated that the details of the atomic structure can play a significant role in HHG.…”

Resonant enhancement of the harmonic-generation spectrum of beryllium

“…These investigations have focused primarily on the HHG spectrum of the He atom [36][37][38][39], although recently HHG results have been reported also for the Ar + ion [40,41]. Various theoretical formulations have been employed: Guan et al [36] use a time-dependent generalized pseudospectral approach in hyperspherical coordinates; Gilary et al [37] use a Floquet-type formulation; we have solved the time-dependent, two-electron Schrödinger equation by means of an eigenstate expansion within a finite radial box [38] (see also Refs.…”

Population trapping in bound states during IR-assisted ultrafast photoionization ofNe+

“…In the study of noble-gas ions, this theory was first applied to the study of two-photon ionization of Ne + in short high-frequency pulses, where it was demonstrated how the two-photon ionization rate can be deduced from ionization yields, when absorption of a single photon is just insufficient to achieve ionization [17]. The theory has since been applied primarily to investigate the effect of the interplay between closely spaced residual-ion thresholds on harmonic generation for Ar + and Ne + [11,12,18]. These studies demonstrated that the accurate description of harmonic generation requires at least inclusion of the np 4 3 P e and 1 D e thresholds.…”