Hannover 2013 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 45: Atomic systems in external fields I

A 45.1: Hauptvortrag

Freitag, 22. März 2013, 11:00–11:30, B 302

Attosecond time-resolved high-resolution spectroscopy of two-electron dynamics in helium, and impulsive control of light — •Thomas Pfeifer — MPI für Kernphysik, Heidelberg

The dynamical motion of electrons governs the physics of processes as fundamental as the absorption of visible light (e.g. creating color) and the making and breaking of molecular bonds (e.g. chemical reactions). In almost all atoms or molecules, electronic excitations are based on the concerted, quantum-correlated, motion of two or more electrons, due to the strong and long-range electron--electron Coulomb interaction and the fermionic exchange symmetry (Pauli principle). It has thus been a long-standing dream to temporally resolve, understand, and control the correlated quantum-mechanical wave function of two or more electrons. Here, we present an experimental spectroscopy method to measure this correlated motion of two electrons bound to a Helium atom. By using tunable laser intensity, we directly observe the continuous transition from weak and perturbative to strong coupling with Rabi cycling (Autler--Townes doublet formation) among autoionizing states. We also use our measurement scheme and its sensitivity to the quantum phase of the excited states to reconstruct a two-electron wavepacket, which can be shaped by the visible laser field, with corresponding implications for the control of covalent molecular bonds, typically consisting of two electrons. We also find a mechanism to variably tune the Fano absorption profiles (inversion and Lorentz-profile conversion), which has far-reaching consequences for the control of absorption of radiation throughout the entire spectrum in general.