Absolute triple differential cross sections for photo-double ionization of helium - experiment and theory

Abstract

We have measured absolute triple differential cross sections for photo-double ionization of helium at 20 eV excess. The measurement covers the full ranges of energy sharing and emission angles of the two photoelectrons. We compare our data for selected geometries with the convergent close-coupling (CCC) calculations as well as 2SC calculations by Pont and Shakeshaft and 3C calculations by Maulbetsch and Briggs. In terms of the absolute magnitude and the trend in the shapes of the triple differential cross section for different geometries we find good agreement of the CCC and published 2SC calculations with our measurement, though differences with respect to the observed shape of individual patterns still exist.

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

“…(11) for ω XUV = 99 eV and detection of one electron at fixed angles θ 1 = 0 • , 30 • , and 60 • relative to the XUV-pulse polarization direction as a function of the other electron's emission angle θ 2 . Our calculated conditional TDCSs for coplanar emission are in good agreement with measured absolute conditional angular distributions [6,34]. For θ 1 = 0 • , our TDCSs for equal energy sharing [ Fig.…”

“…For nonequal energy sharing, electron correlation in the final state tends to be less important than for equal energy sharing. By free propagation to T f = 40 we therefore expect the calculated energy and angular distributions at nonequal energy sharing discussed in this work to be accurate within the error limits in typical double-ionization experiments [6].…”

“…The first measurement of the triply differential cross section (TDCS) for direct (nonsequential) single-photon double photoionization in helium at equal energy sharing of the emitted electrons was reported by Schwarzkopf et al [3]. The TDCS for single-photon DI at unequal energy sharing was measured subsequently by Schwarzkopf et al [4,5] and Bräuning et al [6]. Due to their extremely small values, the measurement of two-photon DI cross sections has remained a challenge in the laboratory.…”

“…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.…”

Single and triple differential cross sections for double photoionization ofH−

“…Recent experimental investigations have focused on double photoionization (DPI) of two-electron atoms [1][2][3][4][5][6][7] and molecules [8][9][10][11] as a sensitive probe of the correlated motion of electrons. The DPI problem is interesting from both experimental and theoretical viewpoints because the process by which an atom or molecule absorbs a photon of sufficient energy to eject two electrons into the continuum necessarily depends on electron correlation.…”