Bonn 2025 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 1: Atomic Systems in External Fields I
A 1.2: Hauptvortrag
Montag, 10. März 2025, 11:30–12:00, KlHS Mathe
Circular dichroism in multiphoton ionization of resonantly excited helium ions near channel closing — •Niclas Wieland1, Rene Wagner1, Markus Ilchen1, Nicolas Douguet2, Philipp Schmidt3, Klaus Bartschat4, and Michael Meyer3 — 1Department of Physics, Universität Hamburg — 2Department of Physics, University of Central Florida — 3European X-Ray Free-Electron Laser Facility — 4Department of Physics and Astronomy, Drake University
Circulardichroism (CD) in photoionization experiments offers a unique window into the dynamics of light-matter interaction, enabling the study of symmetry, resonances, and transient states of matter. In this talk, I will present our investigation of the CD of photoelectrons generated by near-infrared (NIR) laser pulses through multiphoton ionization of excited He+ ions in the 3p (m = +1) state, prepared by circularly polarized extreme ultraviolet (XUV) pulses. By comparing co- and counter-rotating NIR pulse configurations relative to the XUV polarization, we observe a complex dependence of CD on the laser intensity and polarization. These effects are linked to Freeman resonances, selectively influenced by dichroic AC-Stark shifts, which alter the photoionization pathways.
Through experimental results and numerical simulations based on the time-dependent Schrödinger equation, we identify the mechanisms driving this variation in CD. Our findings emphasize the role of intermediate resonances in steering photoionization dynamics and highlight He+ as a benchmark system for exploring fundamental dichroic effects.
Keywords: Circular dichroism; photoionization experiment; Freeman resonances