Formation of very low energy states crossing the ionization threshold of argon atoms in strong mid-infrared fields

Abstract

Atomic ionization by intense mid-infrared (mid-IR) pulses produces low electron energy features that the strong-field approximation, which is expected to be valid in the tunneling ionization regime characterized by small Keldysh parameters ($\gamma \ll 1$), cannot describe. These features include the low-energy structure (LES), the very-low-energy structure (VLES), and the more recently found zero-energy structure (ZES). They result from the interplay between the laser electric field and the atomic Coulomb field which controls the low-energy spectrum also for small $\gamma$. In the present joint experimental and theoretical study we investigate the vectorial momentum spectrum at very low energies. Using a reaction microscope optimized for the detection of very low energy electrons, we have performed a thorough study of the three-dimensional momentum spectrum well below 1 eV. Our measurements are complemented by quantum and classical simulations, which allow for an interpretation of the LES, VLES and of the newly identified ZES in terms of two-dimensional Coulomb focusing and recapture into Rydberg states, respectively.

arXiv comment18 pages, 7 figures

References in corpus (5)

• Origin of Unexpected Low Energy Structure in Photoelectron Spectra Induced by Mid-Infrared Strong Laser Fields
• Electron-energy bunching in laser-driven soft recollisions
• Self-compression to sub-3-cycle duration of mid-infrared optical pulses in bulk
• Low-energy peak structure in strong-field ionization by mid-infrared laser-pulses: two-dimensional focusing by the atomic potential
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• Maximum information photoelectron metrology
• Semiclassical two-step model for ionization by a strong laser pulse: Further developments and applications
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• Density-based one-dimensional model potentials for strong-field simulations in $\text{He}$, ${\text{H}}_2^{+}$ and ${\text{H}}_2$
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• Strong field ionisation of Argon: Electron momentum spectra and nondipole effects