Strong-field extreme-ultraviolet dressing of atomic double excitation

• Main Authors: Ott, Christian, Aufleger, Lennart, Ding, Thomas, Rebholz, Marc, Magunia, Alexander, Hartmann, Maximilian, Stooß, Veit, Wachs, David, Birk, Paul, Borisova, Gergana Dimitrova, Meyer, Kristina, Rupprecht, Patrick, da Costa Castanheira, Carina, Moshammer, Robert, Attar, Andrew R., Gaumnitz, Thomas, Loh, Zhi Heng, Düsterer, Stefan, Treusch, Rolf, Ullrich, Joachim, Jiang, Yuhai, Meyer, Michael, Lambropoulos, Peter, Pfeifer, Thomas
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2020
• Subjects: Science::Physics; Autoionization & Auger proesses; Stark Effect
• Online Access: https://hdl.handle.net/10356/141912
• Institution: Nanyang Technological University

We report on the experimental observation of a strong-field dressing of an autoionizing two-electron state in helium with intense extreme-ultraviolet laser pulses from a free-electron laser. The asymmetric Fano line shape of this transition is spectrally resolved, and we observe modifications of the resonance asymmetry structure for increasing free-electron-laser pulse energy on the order of few tens of Microjoules. A quantum-mechanical calculation of the time-dependent dipole response of this autoionizing state, driven by classical extreme-ultraviolet (XUV) electric fields, evidences strong-field-induced energy and phase shifts of the doubly excited state, which are extracted from the Fano line-shape asymmetry. The experimental results obtained at the Free-Electron Laser in Hamburg (FLASH) thus correspond to transient energy shifts on the order of a few meV, induced by strong XUV fields. These results open up a new way of performing nonperturbative XUV nonlinear optics for the light-matter interaction of resonant electronic transitions in atoms at short wavelengths.