Photoelectron Angular Distributions of Nonresonant Two-Photon Atomic Ionization Near Nonlinear Cooper Minima

Jiri Hofbrucker,Latifeh Eiri,Stephan Fritzsche,Andrey V Volotka

doi:10.3390/atoms8030054

Abstract

Photoelectron angular distributions of the two-photon ionization of neutral atoms are theoretically investigated. Numerical calculations of two-photon ionization cross sections and asymmetry parameters are carried out within the independent-particle approximation and relativistic second-order perturbation theory. The dependence of the asymmetry parameters on the polarization and energy of the incident light as well as on the angular momentum properties of the ionized electron are investigated. While dynamic variations of the angular distributions at photon energies near intermediate level resonances are expected, we demonstrate that equally strong variations occur near the nonlinear Cooper minimum. The described phenomena is demonstrated on the example of two-photon ionization of magnesium atom.

Highlights

Over the last few decades, studies of nonlinear light-matter interaction have received much attention, both theoretically [1,2,3,4,5,6,7,8,9] as well as experimentally [10,11,12,13,14]
We have demonstrated that the maximum of elliptical dichroism in photoelectron angular distributions appears near the nonlinear Cooper minimum [5]
The purpose of this paper is to clearly demonstrate the strong effect of nonlinear Cooper minimum upon photoelectron angular distributions in non-resonant two-photon ionization of atoms

Summary

Introduction

Over the last few decades, studies of nonlinear light-matter interaction have received much attention, both theoretically [1,2,3,4,5,6,7,8,9] as well as experimentally [10,11,12,13,14]. With the advancement of extreme ultraviolet (EUV) and X-ray light sources such as free-electron lasers (FELs) [15,16,17], energy restrictions of optical lasers have been removed and new opportunities to investigate ionization of inner-shell electrons of atoms and molecules arose [18]. FELs are capable of generating high-brilliance X-ray beams, which enables one to explore the inner-shell electron dynamics [19] and the multi-photon ionization [11,20]. Modern FEL facilities are even capable to tune the polarization of the intense high-energy beams, which open novel experimental possibilities to investigate the dichroic nature of multi-photon ionization as well as molecular chirality at xuv and X-ray photon energies [21,22]. Two-photon ionization can be studied by either detecting the yields of the emitted photoelectrons [23,24], or produced photoions [25] or by collecting the subsequent fluorescence as observed for the two-photon

Objectives

Results

Conclusion