Calculations of total photoionization cross-section for^M two-electron atomic systems

Without a formal derivation, we propose a formula for the total and single-differential cross in the problem of one-photon double ionization of an atom. The formula is benchmarked against accurate experimental data for the total cross section of helium. Furthermore, a direct comparison with ab initio calculations for the double ionization of Li+ suggests that the framework is valid for the entire helium isoelectronic sequence. To this end, we introduce a formula for the doubl...

Using extreme-ultraviolet attosecond-pulse-trains, we investigate the photoionization dynamics of a Helium atom in the presence of moderately-strong (~10^12 W/cm^2) femtosecond laser pulses. The electronic structure of a laser-dressed atom is traced in real-time through precision measurements of ion-yields and photo-electron angular distributions. Quantum interferences between photo-excitation paths are interpreted using the Floquet formalism. As the laser pulse intensity ram...

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 wit...

A methodology is developed to compute photoionization cross-sections beyond the electric dipole (BED) approximation from response theory, using Gaussian type orbitals and plane waves for the initial and final states, respectively. The methodology is applied to compute photoionization cross-sections of atoms and ions from the first four rows of the Periodic Table. Analysing the error due to the plane wave description of the photoelectron, we find kinetic energy and concomitant...

The relations between photoionization cross sections and photon radius are obtained on basis of quantum mechanics and the particle-like properties of a photon. The photoionization cross sections of H atom and H-like ions, He atom and He like ions, alkali metal atoms, and Rydberg atoms are calculated using the relations. The calculation results are found to be good agreement with the known experimental data. The results show that the photoionization cross section is always sma...

We describe a method for the calculation of photoionization cross-sections using square-integrable amplitudes obtained from the diagonalization of finite-basis set representations of the electronic Hamiltonian. Three examples are considered: a model example in which the final state is a free particle, the hydrogen atom and neutral atomic sodium. The method exploits the Whittaker-Shannon-Kotel'nikov sampling theorem, which is widely used in digital signal sampling and reconstr...

We account for the different symmetries of the 2^{1,3}S helium excited states in a quasiclassical description of the knockout mechanism augmented by a quantum shakeoff contribution. We are thus able to formulate the separate contribution of the knockout and shakeoff mechanisms for double photoionization for any excess energy from the 2^{1,3}S states. Photoionization ratios and singly differential cross sections calculated for the 2^{1,3}S excited states of helium are found to...

Partial autoionization rates of doubly excited one-dimensional helium in the collinear Zee and eZe configuration are obtained by means of the complex rotation method. The approach presented here relies on a projection of back-rotated resonance wave functions onto singly ionized $\textrm{He}^{+}$ channel wave functions and the computation of the corresponding particle fluxes. In spite of the long-range nature of the Coulomb potential between the electrons and the nucleus, an a...

It is shown that it is feasible to use ultrashort time delay between two XUV femtosecond pulses in order to control two photon resonant ionization. The proposal is demonstrated on the spectrum of Helium, in terms of nonperturbative solutions of the time dependent Schroedinger equation. Comparison with results from second order time dependent perturbation theory provides additional insight.

Photodetachment of the outer-most electrons in few- and many-electron atomic systems is studied in the non-relativistic dipole approximation. Such a photodetachment is analyzed for the neutral atoms and positively charged atomic ions. We also investigate photodetachment of the outer-most electrons in the negatively charged atomic ions, including the negatively charged hydrogen ion. In all these cases we have derived the closed analytical formulas for the photodetachemnt cross...