Polarization Effects in Laser-Assisted (e,2e) Collision on H-atom by Twisted Electrons

Abstract

The dynamics of fast (e, 2e) collisions, induced by the impact of twisted electron beams, on atomic hydrogen, is analyzed in the presence of a laser field with circular and linear polarization. For the (e,2e) differential cross-section calculations we use Volkov and Coulomb-Volkov wave functions for scattered and ejected electrons, respectively, while the laser-atom interaction is treated in first-order perturbation theory. The formalism is developed for the asymmetric coplanar geometry in the first Born approximation. We investigate the influence of laser field polarization and provide a comparative analysis of Triple Differential Cross-Sections (TDCS) for circularly and linearly polarized laser fields as a function of ejected electron angle. The overall magnitude of the cross-section is larger for circular polarization as compared to linear polarization. Some notable changes in the angular distributions of TDCS were also observed for the circular polarization as compared to that for linear polarization. We further extend the study to coherent superpositions of twisted electron beams to examine OAM effects for macroscopic target which shows that the TDCS$_{av}$ is strongly sensitive to the difference of the projectiles OAM as well as on the phase difference between them.

Figures (10)

• Figure 1: Schematic illustration of the kinematic geometry for the laser-assisted (e,2e) reaction on atomic hydrogen. The incident electron momentum $\mathbf{k}_i$ is aligned along the $z$-axis, and $zx$ plane defines the scattering plane. (a) Configuration for linear polarization, where the electric field polarization vector $\boldsymbol{\varepsilon}$ is oriented parallel to the momentum transfer vector $\boldsymbol{\Delta}$. (b) Configuration for circular polarization ($\mathrm{CP_Y}$), where the laser field propagates along the $y$-axis ($\mathbf{k} \parallel \hat{y}$), such that the electric field vector $\boldsymbol{\varepsilon}$ rotates within the $zx$ scattering plane.
• Figure 2: Angular distributions of the Triple Differential Cross Section (TDCS) plotted against the ejected electron angle $\theta_e$. The study compares three interaction regimes: the Field Free ($\mathrm{FF}$) case (solid curve), laser-assisted collisions in a Linearly Polarized ($\mathrm{LP}$) field (blue dotted curve), with the polarization vector parallel to the momentum transfer direction; and laser-assisted collisions in a Circularly Polarized ($\mathrm{CP_Y}$) field (red dashed curve), with the polarization vector aligned along the $y$-axis within the scattering ($zx$) plane. Kinematic parameters are fixed at incident energy $E_i = 600$ eV, ejected energy $E_e = 5$ eV, and scattering angle $\theta_s = 4^\circ$. Laser parameters correspond to the absorption of $l = 1$ photon with field strength $\varepsilon = 10^6$ V/m and photon energy $\hbar\omega = 1.17$ eV. The specific scaling factors are indicated in the panel to compare with the field free results.
• Figure 3: Angular distributions of the Triple Differential Cross Section (TDCS) for orbital angular momentum $m_l$ = 1, plotted against the ejected electron angle $\theta_e$. The study compares three interaction regimes: (a) the Field Free ($\mathrm{FF}$) case; (b) laser-assisted collisions in a Linearly Polarized ($\mathrm{LP}$) field, with the polarization vector parallel to the momentum transfer direction; and (c) laser-assisted collisions in a Circularly Polarized ($\mathrm{CP_Y}$) field, with the polarization vector aligned along the $y$-axis within the scattering ($zx$) plane. The curves denote opening angles of $\theta_p = 1^\circ$ (solid green), $\theta_p = 4^\circ$ (blue dotted), and $\theta_p = 15^\circ$ (red dashed). Kinematic parameters are same as the fig \ref{['1']}.
• Figure 4: Kinematics is same as figure \ref{['fig:3']} except the $m_l$ = 2
• Figure 5: Kinematics is same as figure \ref{['fig:3']} except the $m_l$ = 3