Abstract
We study the double ionization of atoms subjected to circularly polarized (CP) laser pulses. We analyze two fundamental ionization processes: the sequential (SDI) and nonsequential (NSDI) double ionization in the light of the rotating frame (RF) which naturally embeds nonadiabatic effects in CP pulses. We use and compare two adiabatic approximations: The adiabatic approximation in the laboratory frame (LF) and the adiabatic approximation in the RF. The adiabatic approximation in the RF encapsulates the energy variations of the electrons on subcycle timescales happening in the LF and this, by fully taking into account the ion-electron interaction. This allows us to identify two nonadiabatic effects including the lowering of the threshold intensity at which over-the-barrier ionization happens and the lowering of the ionization time of the electrons. As a consequence, these nonadiabatic effects facilitate over-the-barrier ionization and recollision-induced ionizations. We analyze the outcomes of these nonadiabatic effects on the recollision mechanism. We show that the laser envelope plays an instrumental role in a recollision channel in CP pulses at the heart of NSDI.
Highlights
Intense laser pulses generate forces which are potentially comparable to Coulomb forces inside atoms and molecules
We have investigated some features of the double ionization of atoms subjected to intense circularly polarized laser pulses
We have shown that the parameter μ ∝ |E1|3λ2 monitors the amount of nonadiabatic effects for over-the-barrier ionization
Summary
Intense laser pulses generate forces which are potentially comparable to Coulomb forces inside atoms and molecules. The adiabatic approximation in the RF naturally embeds the energy variations of the electron on subcycle timescales happening in the LF, and by fully taking into account the ion-electron interactions This allows us to identify two nonadiabatic effects in the ionization process (compared with the adiabatic approximation): The lowering of the threshold intensity for which over-the-barrier ionization occurs, and the lowering of the ionization time of the electrons in the over-thebarrier ionization regime. We derive the conditions under which over-the-barrier ionization occurs and the release times of the electrons as a function of the laser and atomic parameters by accounting for the electron energy variations on subcycle timescales happening in the RF. IV, we derive the conditions under which recollisions can be observed in CP pulses
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