Hannover 2020 – scientific programme
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A: Fachverband Atomphysik
A 23: Interaction with VUV and X-ray light I
A 23.2: Talk
Thursday, March 12, 2020, 11:30–11:45, f107
Cooper minimum in multi-photon ionization — •Jiri Hofbrucker1,2,3, Andrey Volotka2,3, and Stephan Fritzsche1,2,3 — 1Friedrich-Schiller University, Jena, Germany — 2Helmholtz Institute, Jena, Germany — 3GSI, Darmstadt, Germany
In one-photon ionization, the photon energy for which the dominant ionization channel vanishes is called the Cooper minimum. This concept is extended to nonlinear ionization of atoms. We study this nonlinear Cooper minimum in the two-photon ionization process. In our talk it will be shown that the nonlinear Cooper minimum leads to strong variation in practically all observable quantities of the two-photon ionization process. For example, by tuning the incident photon energy to the nonlinear Cooper minimum, it is possible to enhance the polarization transfer from the incident light to the photoion. The ion polarization can be observed either directly, or in the case of inner-shell ionization, via polarization of subsequent fluorescence and Auger decay particles. The nonlinear Cooper minimum also leads to the maximum elliptical dichroism in photoelectron angular distributions. As all the mentioned quantities are normalized quantities, they are less sensitive to experimental uncertainties. It is theorized that detection of the energy position of the nonlinear Cooper minimum via one of the mentioned methods could lead to comparison of experimental measurements and theoretical calculations at hitherto unreachable accuracy.