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Abstract

Within this work, the bound-state dynamics of systems with correlated electrons in external electric fields are experimentally observed and numerically understood on their natural attosecond time scale. The time-resolved measurements were carried out with the method of attosecond transient absorption spectroscopy. The spectra obtained by this scheme feature signatures that depend on time delay between and the intensity of the used laser pulses. Disentangling and understanding the various contributions to these features is the key to gain information about the behavior of atomic and molecular systems in strong external fields and the induced couplings and electronic dynamics. This work offers an explanation for the physical origin of prominent features which are caused by the effect of strong, rapidly-oscillating electric fields on the bound state dynamics of two-electron systems. The results are based on experiments performed on singly-excited Helium atoms and the numerical calculation of an one-dimensional Schrödinger equation. The spectral features appear due to instantaneous polarization and breaking of the symmetry of the atom following the electric field of the infrared-femtosecond pulse used in our transientabsorption setup and, therefore, give access to the symmetry properties of the atomic system. Measurements in singly excited Helium revealed the contribution of this polarization effect to light-induced states in the region of temporal and spatial pulse-overlap. Using this effect, the onset of symmetry-breaking for low-lying states in Helium by a strong electric field was directly observed.