Observation of transition radiation carrying orbital angular momentum

TL;DR

This paper reports the first observation of transition radiation carrying orbital angular momentum generated by relativistic electrons interacting with a solid target, expanding the methods for producing twisted photons.

Contribution

It demonstrates that twisted photons with orbital angular momentum can be generated via transition radiation from rectilinear electron motion, a novel method compared to prior approaches.

Findings

First observation of transition radiation with orbital angular momentum

Orbital angular momentum measured through diffraction patterns

Generation of twisted photons from solid target interaction

Abstract

Twisted photons carrying orbital angular momentum, which have potential applications spanning diverse fields, have been extensively studied since the theoretical work of Allen \textit{et al}. in 1992. Various methods for direct producing twisted photons have been explored, leveraging the rotational (spiral) motion of relativistic electrons in phenomena such as undulator radiation. In the present study, transition radiation carrying orbital angular momentum is observed for the first time. This radiation was generated by 220 MeV electrons incident on an Au-coated Si wafer. The orbital angular momentum was measured by analyzing the diffraction patterns produced as the radiation passed through a triangular aperture and a double slit. These results demonstrate that twisted photons can also be generated through the interaction of rectilinearly moving electrons with a solid target.