Nonadiabatic effects in the double ionization of atoms driven by a circularly polarized laser pulse

TL;DR

This paper investigates nonadiabatic effects in double ionization of atoms under circularly polarized laser pulses, revealing how these effects influence ionization thresholds and recollision mechanisms, with implications for understanding strong-field ionization processes.

Contribution

It introduces an adiabatic approximation in the rotating frame that captures nonadiabatic effects in circularly polarized laser-driven ionization, advancing the theoretical understanding of these phenomena.

Findings

Nonadiabatic effects lower ionization thresholds.

Nonadiabatic effects reduce electron ionization times.

Laser envelope significantly influences recollision channels.

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 non-sequential (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.