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 10U.