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A: Fachverband Atomphysik

A 2: Interaction with strong or short laser pulses I

A 2.4: Vortrag

Montag, 14. März 2022, 15:00–15:15, A-H1

Making non-adiabatic photoionization adiabatic — •Jonathan Dubois, Ulf Saalmann, and Jan-Michael Rost — Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany

We consider the process of tunnel ionization of atoms driven by circularly polarized (CP) pulses. An intuitive semiclassical picture of tunnel ionization by a static laser field is an electron ionizing through the potential barrier induced by the laser field with constant energy, referred to as the adiabatic ionization. When the laser field alternates in time, such as it is the case for CP pulses, the energy of the electron changes in time, and at the tunnel exit, it is distributed in a range of energy on the order of the ponderomotive energy of the laser. The adiabatic picture no longer holds, and the ionization process is referred to as nonadiabatic. Extensive theoretical and experimental studies are performed in the attosecond community to probe and understand these nonadiabatic effects in photoionization.

Our goal is to understand nonadiabatic processes in CP pulses using electron trajectories in the combined laser and Coulomb fields. We map the electron dynamics in a frame which rotates with the laser field, referred to as the rotating frame (RF). Our results show that in the RF, counter-intuitively, the energy of the electron is constant during tunnel ionization, and as a consequence follows the picture of adiabatic ionization. This allows us to understand and predict, for instance, the role played by ring currents in atoms and the shape of the laser envelope, and to shed light on classical-quantum correspondence.