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A: Fachverband Atomphysik
A 11: Atomic Systems in External Fields I
A 11.1: Invited Talk
Tuesday, March 3, 2026, 11:00–11:30, N 2
Dichroic Electron Emission Patterns from Oriented Helium Ions — •Niclas Wieland1, Klaus Bartschat2, Filippa Dudda1, Michael Meyer3, and Markus Ilchen1 — 1University of Hamburg, Hamburg, Germany — 2Drake University, Des Moines, USA — 3European X-Ray Free-Electron Laser Facility
We report a joint experimental and theoretical study using a combination of polarization-controlled free-electron-laser (FEL) and near-infrared (NIR) pulses in a synchronized two-color photoionization scheme. Excited He+ ions, created by extreme ultraviolet (XUV) circularly polarized radiation from the XUV-FEL FERMI in the oriented 3p (m = +1) state, are exposed to circularly polarized 784-nm NIR radiation with peak intensities from 10^12 W/cm^2 to 10^13 W/cm^2. The angular distribution of the ejected electrons exhibits a strong dichroism depending on the NIR intensity. While the co-rotating case is defined by a single path, for the counter-rotating case, there are two dominant pathways whose relative strength and phase difference are determined.
Keywords: Photoionization; Circular Dichroism; Free-electron Laser (FEL); Helium Ions; Two-color ionization