Angular momentum gain by electrons under the action of intense structured light

The problem of the interaction of light waves with charged particles becomes increasingly 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, a description of single-particle dynamics in the focused structured laser beams is the first step and may serve as a good approximation to understand the global plasma response. Moreover, the general problem of integrability in complex systems starts from a 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 which are initially distributed 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.