Transition from strong-field sequential to nonsequential double ionization at near-infrared wavelengths and low intensities |
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Authors: | Kai Liu Meiyan Qin Qianguang Li Qing Liao |
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Institution: | 1.Laboratory for Optical Information Technology,Wuhan Institute of Technology,Wuhan,China;2.School of Physics and Electronic-information Engineering,Hubei Engineering University,Xiaogan,China |
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Abstract: | Within a quantum-mechanical model, we investigate strong-field double ionization of a model helium atom by near-infrared, linearly polarized laser pulses at intensities far below the recollision threshold. The quantum simulations show a clear mechanism change from sequential to nonsequential double ionization (NSDI) as the laser intensity increases. For NSDI, the two-electron correlated momentum distribution exhibits a strong final-state Coulomb repulsion effect for high-energy photoelectrons, but absent for low-energy photoelectrons. This repulsion effect is ascribed to field double ionization from doubly-excited states populated by recollision of the first ionized electron when it returns to the parent ion. Such recollision-induced excited states are absent at ultraviolet wavelengths due to the very low returning kinetic energies, resulting to the absence of final-state repulsion effect in NSDI. |
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