Detecting transition radiation from a magnetic moment

TL;DR

This paper proposes a method to detect magnetic moment radiation using vortex electrons with high orbital angular momentum, predicting measurable asymmetries in transition radiation that could confirm magnetic moment contributions.

Contribution

It introduces a novel experimental approach employing vortex electrons to observe magnetic moment radiation, which has not been experimentally confirmed before.

Findings

Predicted angular asymmetry of 0.1%-1% in transition radiation from vortex electrons.

Magnetic moment contribution becomes dominant with high orbital angular momentum.

Potential for experimental detection with current technology.

Abstract

Electromagnetic radiation can be emitted not only by particle charges but also by magnetic moments and higher electric and magnetic multipoles. However experimental proofs of this fundamental fact are extremely scarce. In particular, the magnetic moment contribution has never been observed in any form of polarization radiation. Here, we propose to detect it using vortex electrons carrying large orbital angular momentum (OAM) \ell. The relative contribution of the OAM-induced magnetic moment, \ell \hbar \omega/E_e, becomes much larger than the spin-induced contribution \hbar \omega/E_e, and it can be observed experimentally. As a particular example, we consider transition radiation from vortex electrons obliquely incident on an interface between a vacuum and a dispersive medium, in which the magnetic moment contribution manifests itself via a left-right angular asymmetry. For electrons with E_e = 300 keV and \ell = 100-1000, we predict an asymmetry of the order of 0.1%-1%, which could be measured with existing technology. Thus, vortex electrons emerge as a new tool in the physics of electromagnetic radiation.