Eur. Phys. J. B (2018) 91: 151
https://doi.org/10.1140/epjb/e2018-90178-5

Regular Article

Natural orbitals of helium in linearly polarized laser fields^★

Institut für Physik, Universität Rostock, 18051 Rostock, Germany

^a e-mail: dieter.bauer@uni-rostock.de

Received: 16 March 2018
Received in final form: 8 May 2018
Published online: 4 July 2018

Abstract

Practicable equations of motion for the natural orbitals of a spin-singlet helium atom in a linearly polarized laser field are presented. The cylindrical symmetry of the two-electron problem with quantum number M = 0 is shown to yield a sparse expansion of natural orbitals in spherical harmonics. This optimization facilitates the propagation of renormalized natural orbitals of the helium atom. As a demonstration, the equations of motion are solved for a high-harmonic-generation process. In addition to the expected plateau from the single-active-electron picture, the spectrum of emitted radiation features a second plateau at higher harmonic orders.