Cross sections for short-pulse single and double ionization of helium

Abstract

In a previous publication, procedures were proposed for unambiguously extracting amplitudes for single and double ionization from a time-dependent wavepacket by effectively propagating for an infinite time following a radiation pulse. Here we demonstrate the accuracy and utility of those methods for describing two-photon single and one-photon double ionization of helium. In particular it is shown how narrow features corresponding to autoionizing states are easily resolved with these methods.

Attosecond chronoscopy of photoemission

“…The long-range interaction between the ionized electron and the residual ion in the exit channel contains now both a Coulombic and a dipolar interaction, = − ⃗ ⃗/ 3 . Their direct contributions to EWS in the absence of a streaking field is fully included in the exact calculation of the dipole transition matrix for single ionization of He employing exterior complex scaling (McCurdy et al, 2004;Palacios et al, 2008Palacios et al, , 2009Liertzer et al, 2012). In the presence of a streaking field, however, both long-range portions give additional contributions.…”

Laser-assisted XUV double ionization of helium: Energy-sharing dependence of joint angular distributions

“…Comprehensive numerical studies on the DI of helium following the absorption of a few XUV photons were carried out by Parker et al [16] starting 15 years ago. Following the 2005 experiment of Hasegawa et al [7], two-photon DI of helium has been the subject of several theoretical studies [15,[17][18][19][20][21][22][23][24][25][26][27][28]. In particular, Zhang et al [26] calculated joint angular distributions (JADs) for two-photon DI by XUV pulses in both the nonsequential (39.5 eV < ω XUV < 54.4 eV) and the sequential ( ω XUV > 54.4 eV) regimes for different energy sharings of the emitted electrons.…”

“…Soon afterwards, Briggs and coworkers derived selection rules for helium DI, emphasizing their relevance for the understanding of photoelectron angular distributions [1,[11][12][13][14]. The convergent close-coupling (CCC) calculations by Keifets and Bray [6], TDCSs calculated by Huetz et al [6,10], as well as TDCSs obtained from timedependent close-coupling (TDCC) simulations by Palacios et al [15] were found to be in good agreement with the angular distributions in the absolute TDCSs for the DI of helium by 99 eV XUV photons measured by Bräuning et al [6]. Comprehensive numerical studies on the DI of helium following the absorption of a few XUV photons were carried out by Parker et al [16] starting 15 years ago.…”

Criterion for Distinguishing Sequential from Nonsequential Contributions to the Double Ionization of Helium in Ultrashort Extreme-Ultraviolet Pulses

“…It is enabled by strong electronic correlation and thus clearly distinct from the sequential double-ionization mechanism. Nonsequential double ionization was observed for noble gas atoms in 1982 [2] and received rapidly increasing attention from both experimentalists [3-9] and theorists [10][11][12][13].…”

“…It is enabled by strong electronic correlation and thus clearly distinct from the sequential double-ionization mechanism. Nonsequential double ionization was observed for noble gas atoms in 1982 [2] and received rapidly increasing attention from both experimentalists [3-9] and theorists [10][11][12][13].Photoelectron angular distributions of single-photon double ionization were found to owe their structure partly to (dipole) selection rules [11,14,15] and to consist of symmetrical and antisymmetrical contributions (with regard to electron exchange), that each can be written as the product of an angular and a correlation factor [11]. For coplanar emission geometry, where the emitted-electron momenta and polarization axis of the linearly polarized extremeultraviolet (XUV) pulse lie in a plane, and for equal energy sharing (equal asymptotic kinetic energies E 1 and E 2 of the photoelectrons), the angular factor becomes j cos θ 1 þ cos θ 2 j 2 , where θ 1 and θ 2 are photoelectron emission angles relative to the polarization direction of the ionizing light, while the electron correlation factor follows as expf−4 ln 2½ðθ 12 − πÞ=θ 1=2 2 g, with the mutual emission angle θ 12 ¼ jθ 1 − θ 2 j.…”