Modification of multipole transitions by twisted light

TL;DR

This paper provides a theoretical framework showing how twisted light can modify atomic multipole transitions, introducing a geometrical factor that depends on light properties and atom position, with potential implications for future experiments.

Contribution

It introduces a geometrical factor to describe how twisted light alters multipole transition strengths, independent of atomic shell structure.

Findings

The geometrical factor depends on light's topological charge and kinematic parameters.

Analytical expression derived for Bessel photons and atom position.

Detailed calculations for magnesium atom excitation demonstrate the concept.

Abstract

A theoretical analysis is presented for the excitation of single many-electron atoms and ions by twisted (or vortex) light. Special emphasis is put on excitations that can proceed via several electric and magnetic multipole channels. We argue that the relative strength of these multipoles is very sensitive to the topological charge and kinematic parameters of the incident light and can be strongly modified with respect to the plane-wave case. Most remarkably, the modification of multipole transitions by twisted radiation can be described by means of a geometrical factor. This factor is independent of the shell structure of a particular target atom and just reflects the properties of the light beam as well as the position of an atom with respect to the vortex axis. An analytical expression for the geometrical factor is derived for Bessel photons and for a realistic experimental situation in which the position of an atom is not well determined. To illustrate the use of the geometrical factor for the analysis of (future) measurements, detailed calculations are presented for the $3s3p \, ^3P_1 \to 3s 3p \, ^1P_1$ excitation in neutral Mg.