Strong-field extreme-ultraviolet dressing of atomic double excitation

Abstract

We report on the experimental observation of 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 $\mu$J. A quantum-mechanical calculation of the time-dependent dipole response of this autoionizing state, driven by classical extreme-ultraviolet (XUV) electric fields, reveals a direct link between strong-field-induced energy and phase shifts of the doubly excited state and 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 few meV, induced by strong XUV fields. These results open up a new way of performing non-perturbative XUV nonlinear optics for the light-matter interaction of resonant electronic transitions in atoms at short wavelengths.

16 pages, 3 figures

References in corpus (10)

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• Coherent control with a short-wavelength Free Electron Laser
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Cited by in corpus (7)

• Clocking Auger Electrons
• Strong-field quantum control in the extreme ultraviolet using pulse shaping
• Single-shot MHz velocity-map-imaging using two Timepix3 cameras
• Laser-assisted Fano resonance: attosecond quantum control and dynamical imaging
• Perturbative theory of ensemble-averaged atomic dynamics in fluctuating laser fields
• Non-linear self-driven spectral tuning of Extreme Ultraviolet Femtosecond Pulses in monoatomic materials
• The non-Hermitian landscape of autoionization