Regular Article – Ultraintense and Ultrashort Laser Fields
Linear dichroism in few-photon ionization of laser-dressed helium
Max-Planck-Institute for Nuclear Physics, 69117, Heidelberg, Germany
2 Department of Physics and Astronomy, Drake University, 50311, Des Moines, IA, USA
3 Department of Physics, University of Windsor, N9B 3P4, Windsor, ON, Canada
4 Paul Scherrer Institute, 5232, Villigen, Switzerland
5 Deutsches Elektronen-Synchrotron, 22607, Hamburg, Germany
6 Department of Physics, Kennesaw State University, 30060, Marietta, GA, USA
Accepted: 4 July 2021
Published online: 16 July 2021
Ionization of laser-dressed atomic helium is investigated with focus on photoelectron angular distributions stemming from two-color multi-photon excited states. The experiment combines extreme ultraviolet (XUV) with infrared (IR) radiation, while the relative polarization and the temporal delay between the pulses can be varied. By means of an XUV photon energy scan over several electronvolts, we get access to excited states in the dressed atom exhibiting various binding energies, angular momenta, and magnetic quantum numbers. Furthermore, varying the relative polarization is employed as a handle to switch on and off the population of certain states that are only accessible by two-photon excitation. In this way, photoemission can be suppressed for specific XUV photon energies. Additionally, we investigate the dependence of the photoelectron angular distributions on the IR laser intensity. At our higher IR intensities, we start leaving the simple multi-photon ionization regime. The interpretation of the experimental results is supported by numerically solving the time-dependent Schrödinger equation in a single-active-electron approximation.
© The Author(s) 2021
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