Cherenkov radiation and emission of surface polaritons from charges moving paraxially outside a dielectric cylindrical waveguide

TL;DR

This paper analyzes the radiation emitted by a charged particle moving outside a dielectric cylinder, focusing on Cherenkov radiation, guided modes, and surface polaritons, revealing unique spectral features and conditions for their occurrence.

Contribution

It provides new analytical expressions and insights into surface polariton emission without velocity thresholds and the influence of dielectric properties on spectral distributions.

Findings

Surface polaritons occur without velocity threshold when dielectric permittivities have opposite signs.

Strong narrow peaks can appear in Cherenkov radiation spectra due to the cylinder's presence.

Spectral range of surface polaritons narrows with decreasing particle energy.

Abstract

We investigate the radiation from a charged particle moving outside a dielectric cylinder parallel to its axis. It is assumed that the cylinder is immersed into a homogeneous medium. The expressions are given for the vector potential and for the electric and magnetic fields. The spectral distributions are studied for three types of the radiations: (i) Cherenkov radiation (CR) in the exterior medium, (ii) radiation on the guided modes of the dielectric cylinder, and (iii) emission of surface polaritons. Unlike the first two types of radiations, there is no velocity threshold for the generation of surface polaritons. The corresponding radiation is present in the spectral range where the dielectric permittivities of the cylinder and surrounding medium have opposite signs. The spectral range of the emitted surface polaritons becomes narrower with decreasing energy of the particle. The general results are illustrated for a special case of the Drude model for dispersion of the dielectric permittivity of the cylinder. We show that the presence of the cylinder may lead to the appearance of strong narrow peaks in the spectral distribution of the CR in the exterior medium. The conditions are specified for the appearance of those peaks and the corresponding heights and widths are analytically estimated. The collective effects of particles in bunches are discussed.