Photonic and plasmonic transition radiation from graphene

TL;DR

This paper investigates how swift electrons crossing graphene induce broadband electromagnetic radiation, including photons and plasmons, with findings relevant for designing terahertz on-chip sources.

Contribution

It provides a comprehensive analysis of transition radiation from graphene, deriving spectra analytically and revealing velocity-dependent excitation of photons and plasmons.

Findings

Higher electron velocities excite more directive and intense photons.

Lower velocities favor broad-range graphene plasmon excitation.

The study offers insights for terahertz radiation source design.

Abstract

In the framework of full Maxwell equations, we systematically study the electromagnetic radiation, namely the transition radiation, when a swift electron perpendicularly crosses a monolayer graphene. Based on the plane wave expansion and the Sommerfeld integration, we demonstrate the spatial distribution of this free-electron radiation process in the frequency domain, which clearly shows the broadband excitation of both the photons and graphene plasmons. Moreover, the radiation spectra for the excited photons and graphene plasmons are analytically derived. We find that the excitation of photons and graphene plasmons favours different velocities of the swift electron. To be specific, a higher electron velocity can give rise to the excitation of photons with better directivity and higher intensity, while a lower electron velocity can enable the efficient excitation of graphene plasmons in a broader frequency range. Our work indicates that the interaction between swift charged particles and ultrathin 2D materials or metasurfaces is promising for the design of terahertz on-chip radiation sources.