Parametrizations and dynamical analysis of angle-integrated cross sections for double photoionization including nondipole effects

Abstract

Similarly to differential cross sections for one-electron photoionization, the doubly differential cross section for double photoionization ͑DPI͒ may be conveniently described by four parameters: the singly differential ͑with respect to energy sharing͒ cross section ͑ 0 ͒, the dipole asymmetry parameter ͑␤͒, and two nondipole asymmetry parameters ͑␥ and ␦͒. Here we derive two model-independent representations for these parameters for DPI from a 1 S 0 atomic bound state: ͑i͒ in terms of one-dimensional integrals of the polarization-invariant DPI amplitudes and ͑ii͒ in terms of the exact two-electron reduced matrix elements. For DPI of He at excess energies, E exc , of 100 eV, 450 eV, and 1 keV, we present numerical results for the asymmetry parameters within the framework of the convergent close-coupling theory and compare them with results of lowest-order ͑in the interelectron interaction͒ perturbation theory ͑LOPT͒. The results for E exc = 1 keV exhibit a nondipole asymmetry that is large enough to be easily measured experimentally. We find excellent agreement between our LOPT results and other theoretical predictions and experimental data for total cross sections and ratios of double to single ionization cross sections for K-shell DPI from several multielectron atoms.

About universal scalings in double K-shell photoionization

“…2). The calculations performed by independent theoretical groups are consistent with each other [16,17,18]. Note also that the maxima of the universal functions Z 4 σ ++ and Z 2 σ ++ /σ + peak at different values of the photon energy, namely, at ε γ ≃ 2.5 and 4, respectively.…”

A general algorithm for fitting efficiently triple differential cross sections of atomic double photoionization

“…This result and its generalization to arbitrary states of the target atom and the parent ion have been obtained independently by Manakov et al [9] and Malegat et al [10]. Istomin et al [11][12][13][14] have extended the TDCS parametrization for helium DPI to include also the contributions of the lowest order non-dipole term of the transition operator.…”

Review on non-dipole effects in ionization and harmonic generation of atoms and molecules*

“…In 2003, the observation of PAD in helium photoionization [51,52] confirmed the nondipole parameter can be enhanced by the quadrupole Fano resonance (which does not exist in single electron systems), and a good agreement between the ab initio calculations and experimental measurements was achieved. After several years, the DDCS (simi-013302-5 lar to PAD with a varying energy) of the single photon double ionization (SDPI) is theoretically investigated with the lowest-order perturbation theory and the convergent closecoupling theory (CCC), [188] revealing a nonzero parameter δ , which is usually zero for a single electron photoionization from 1s state. [44] Recently, the nondipole PAD parameters were experimentally observed in the two photon double ionization (TPDI) process in a sequential region using FELs at FERMI, [58] compared with theoretical calculations developed by Grum-Grzhimailo et al [56,189] This study reveals a large nondipole parameter γ…”