On the validity of the paraxial approximation for electron acceleration with radially polarized laser beams

TL;DR

This paper evaluates the accuracy of the paraxial approximation in laser-driven electron acceleration using radially polarized beams, revealing significant differences from exact solutions in key electron beam characteristics.

Contribution

It provides a detailed comparison between exact and paraxial solutions, highlighting the limitations of the paraxial approximation in this context.

Findings

Significant differences in electron angular divergence between solutions

Notable discrepancies in energy distribution of electron bunches

Paraxial approximation may be insufficient for accurate modeling

Abstract

In the study of laser-driven electron acceleration, it has become customary to work within the framework of paraxial wave optics. Using an exact solution to the Helmholtz equation as well as its paraxial counterpart, we perform numerical simulations of electron acceleration with a high-power TM01 beam. For beam waist sizes at which the paraxial approximation was previously recognized valid, we highlight significant differences in the angular divergence and energy distribution of the electron bunches produced by the exact and the paraxial solutions. Our results demonstrate that extra care has to be taken when working under the paraxial approximation in the context of electron acceleration with radially polarized laser beams.