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Mechanism of delayed double ionization

Focus

The simple man picture of an electron which is preionized by a strong linearly polarized laser field and hurled back to the core region where it interacts with the remaining ion was shown to be very effective in explaining abnormally abundant ionization rates as well as high harmonic generation. The returning electron collides with the remaining one, and exchange kinetic energy in order to release it from the Coulomb interaction with the nucleus as in a billiard or petanque game. In this picture, this interaction leads to a little (if any) time delay between the recollision and the subsequent ionization. However, a closer inspection of double ionizations has revealed an unexpected route to double ionization where the time delay between the recollision and subsequent ionization is unexpectedly long, commonly labeled as Recollision Excitation with Subsequent Ionization (or RESI for short). In our Letter, we analyze the mechanisms of delayed double ionization and identify the dynamical structures that regulate this phenomenon. We show that this RESI route to double ionization is a manifestation of Hamiltonian chaos.

Associated publications

Delayed double ionization as a signature of Hamiltonian chaos

posted May 13, 2016, 11:23 PM by François Mauger   [ updated May 13, 2016, 11:23 PM ]

Abstract

We analyze the dynamical processes behind delayed double ionization of atoms subjected to strong laser pulses. Using reduced models, we show that these processes are a signature of Hamiltonian chaos which results from the competition between the laser field and the Coulomb attraction to the nucleus. In particular, we exhibit the paramount role of the unstable manifold of selected periodic orbits which lead to a delay in these double ionizations. Among delayed double ionizations, we consider the case of recollision excitation with subsequent ionization (RESI) and, as a hallmark of this mechanism, we predict oscillations in the ratio of RESI to double ionization yields versus laser intensity. We discuss the significance of the dimensionality of the reduced models for the analysis of the dynamical processes behind delayed double ionization.

Reference

F. Mauger, A. Kamor, C. Chandre, and T. Uzer – Delayed double ionization as a signature of Hamiltonian chaos - Physical review E 85, 066205 (2012)

Mechanism of Delayed Double Ionization in a Strong Laser Field

posted May 13, 2016, 11:16 PM by François Mauger   [ updated May 13, 2016, 11:20 PM ]

Abstract

When intense laser pulses release electrons nonsequentially, the time delay between the last recollision and the subsequent ionization may last longer than what is expected from a direct impact scenario [recollision excitation with subsequent ionization (RESI)]. We show that the resulting delayed ionization stems from the inner electron being promoted to a sticky region. We identify the mechanism that traps and releases the electron from this region. As a signature of this mechanism, we predict oscillations in the ratio of RESI to double ionization yields versus laser intensity.

Reference

F. Mauger, A. Kamor, C. Chandre, and T. Uzer – Mechanism of Delayed Double Ionization in a Strong Laser Field - Physical Review Letters 108, 063001 (2012)

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