Angular momentum gain by electrons under action of intense structured light

TL;DR

This paper investigates how electrons gain orbital angular momentum when interacting with intense structured light, developing a theoretical model and numerical simulations to understand the underlying physics and effects.

Contribution

It introduces a theoretical model and high-order perturbative approach to analyze electron OAM absorption in focused structured laser beams, including solutions to Maxwell's equations.

Findings

OAM transfer is of fourth order in field amplitude for azimuthally symmetric electron distributions.

Accurate modeling requires considering the temporal envelope of laser pulses.

Numerical simulations confirm the theoretical predictions.

Abstract

The problem of light waves interaction with charged particles becomes more and more complex starting with the case of plane waves, where the analytical solution is well known, to more natural, though more complicated situations which include focused or structured laser beams. Internal structure may introduce a new degree of freedom and qualitatively change the dynamics of interacting particles. For certain conditions, namely for the dilute plasma, description of single-particle dynamics in the focused structured laser beams is the first step and may serve as a good approximation on the way of understanding the global plasma response. Moreover, the general problem of integrability in complex systems starts from consideration of the integrals of motion for a single particle. The primary goal of this work is an understanding of the physics of the orbital angular momentum (OAM) absorption by a single particle in a focused structured light. A theoretical model of the process, including solutions of Maxwell equations with the required accuracy and a high-order perturbative approach to electron motion in external electromagnetic fields, is developed and its predictions are examined with numerical simulations for several exemplary electromagnetic field configurations. In particular, it was found that for the particles distributed initially with the azimuthal symmetry around the beam propagation direction, the transferred OAM has a smallness of the fourth order of the applied field amplitude, and requires an accurate consideration of the temporal laser pulse envelope.