Multipolar expansion of orbital angular momentum modes

TL;DR

This paper introduces a general method for expanding paraxial beams with orbital angular momentum into multipolar electromagnetic fields, linking paraxial OAM to the wave's total angular momentum and extending to highly focused beams, with applications in atomic transitions.

Contribution

It presents a novel, general expansion method for paraxial OAM beams into multipolar fields, applicable to highly focused laser beams and relevant for atomic transition control.

Findings

The method effectively relates paraxial OAM to electromagnetic angular momentum.

Extension of the method to quasi-paraxial, highly focused beams.

Potential applications in controlling electronic transitions in atoms.

Abstract

In this letter a general method for expanding paraxial beams into multipolar electromagnetic fields is presented. This method is applied to the expansion of paraxial modes with orbital angular momentum (OAM), showing how the paraxial OAM is related to the general angular momentum of an electromagnetic wave. This method can be extended to quasi-paraxial beams, i.e. highly focused laser beams. Some applications to the control of electronic transitions in atoms are discussed.