Multi-Electron Quantum Dynamics in Weak and Strong Fields

The correlated motion of two or more electrons in response to an external electric field is a fundamental quantum-dynamical process. Investigating such dynamics in small atoms (e.g., helium and neon) serves as a building block towards a better understanding of light–matter interaction in general, and contributes a bottom-up approach towards the ultimate goal of controlling correlated electron dynamics in more complex systems, such as Mott-type metal-insulator phase-transition dynamics [1] to name only one example. In our labs we use moderately strong (intensity on the order of 1012 to 1013 W/cm2) near-infrared laser pulses of few-femtosecond duration, precisely timed with attosecond extreme-ultraviolet (EUV) pulses (energy range: 40 to 70 eV) to access the intrinsic time and energy scales of the associated electron dynamics. We have demonstrated how to extract quantum amplitude and phase information directly from the experimentally measured EUV absorption spectra, for instance for the case of two-electron doubly excited states in helium and their autoionization dynamics, which lead us to a unified time-domain understanding of Fano and Lorentzian spectral line shapes [2]. This in turn could be applied to explore the laser-control of a two-electron wave packet in helium on the attosecond time scale [3]. In this talk I will give an overview of our activities, also emphasizing on our recent findings to extract the EUV-induced and NIR-controlled dipole response on the femtosecond time scale directly from the measured absorption spectra, most importantly without the need for scanning any pump–probe temporal delays. Finally, as an outlook, I will report on our recent activities exploring the absorption response of helium and neon to strong EUV-only fields at the Free-Electron-Laser in Hamburg (FLASH), where we have also observed and identified significant spectral modifications. All these investigations are at the heart of atomic quantum physics for a better understanding of the interaction of few photons with few electrons in general. [1] M. F. Jager, C. Ott, P. M. Kraus, C. J. Kaplan, W. Pouse, R. E. Marvel, R. F. Haglund, D. M. Neumark, and S. R. Leone, PNAS 114, 9558 (2017). [2] C. Ott, A. Kaldun, P. Raith, K. Meyer, M. Laux, J. Evers, C. H. Keitel, T. Pfeifer, Science 340, 716 (2013). [3] C. Ott, A. Kaldun, L. Argenti, P. Raith, K. Meyer, M. Laux, Y. Zhang, A. Blättermann, S. Hagstotz, T. Ding, R. Heck, J. Madronero, F. Martín, T. Pfeifer, Nature 516, 374 (2014).