Electron correlation and recollision dynamics in nonsequential double ionization by counter-rotating two-color elliptically polarized laser fields

Attosecond Rescattering of Laser-Assisted Electron-Proton Collision in Coulomb Potential

This study investigates the motion of an electron in a Coulomb potential driven by an intense linearly polarized XUV laser pulse analyzed using Gordon-Volkov wave functions. The wave function is decomposed into spherical partial waves to model the scattered electron wave packet after the recollision with a proton. This interaction triggers high harmonic generation, producing coherent X-ray pulses with frequencies that are integer multiples of the XUV field. The research presents a novel method for achieving atomic-scale resolution at nanometer and subfemtosecond levels, enabling observation of electron-proton collisions on an attosecond time scale. It emphasizes the coupling of fields that create resonances in the scattered electron through photon energy exchange with XUV and X-ray pulses, leading to the formation of a Rydberg electron with energy levels up to n = 27 and angular momentum components l = 13 and m = ± 1. The combination of XUV and high-frequency X-ray fields introduces new nonperturbative nonlinear phenomena characterized by differential cross sections derived using the Floquet-Lippmann-Schwinger equation in the first-order Born approximation. The analysis shows that backward-forward scattering involves XUV-electron energy exchange, with peak intensity along the laser polarization vector, while sideways scattering, dominated by X-ray-electron interaction, peaks perpendicular to the polarization. Additionally, the laser-assisted scattering process results in temporary electron capture in a dressed proton-bound state, followed by escape and ejection, with the free electron ponderomotive energy exceeding 10Up.

Enhancement and suppression of nonsequential double ionization by spatially inhomogeneous fields

Using the three-dimensional classical ensemble approach, we theoretically investigate the nonsequential double ionization of argon atoms in an intense laser field enhanced by bowtie-nanotip. We observe an anomalous decrease in the double ionization yield as the laser intensity increases, along with a significant gap in the low momentum of photoelectrons. According to our theoretical analysis, the finite range of the induced field by the nanostructure is the fundamental cause of the decline in double ionization yield. Driven by the enhanced inhomogeneous field, energetic electrons can escape from the finite range of nanotips without returning. This reduces the possibility of re-scattering on the nucleus and imprints the finite size effect into the double ionization yield and momentum distribution of photoelectrons in the form of yield decline and a gap in the photoelectron-momentum distribution.

The Coulomb effect in nonsequential double ionization by counter-rotating two-color elliptical polarization fields

Using a three-dimensional classical ensemble model, nonsequential double ionization (NSDI) of Ar atoms by counter-rotating two-color elliptical polarization (TCEP) fields is investigated. The major axes of the two elliptical fields are aligned in different directions. The relative alignment of the two elliptical fields strongly affects the waveform of the combined electric field and the ultrafast dynamics of NSDI in TCEP fields. Numerical results show that the correlated electron momentum distributions in the x direction evolve from a V-shaped structure near the axis to a distribution concentrated on the diagonal with the angle between the two elliptical major axes increasing. The asymmetry of the energy sharing between the two electrons during recollision results in the V-shaped structure in the correlated momentum spectrum. Back analysis indicates that the recollision times of a part of the trajectories move from the peak to the valley of the combined electric field with the angle between the two elliptical major axes increasing. Therefore, for the case of a larger angle between the two elliptical major axes, the electrons experience a longer time to escape away from the vicinity of the parent ion and thus the stronger Coulomb effect from the parent ion makes the momentum difference between two electrons small, which results in a distribution concentrated on the diagonal. This provides an effective avenue to control the electron ultrafast dynamics in NSDI.