介质圆柱波导外傍轴运动电荷的切伦科夫辐射和表面极化激元发射
Cherenkov radiation and emission of surface polaritons from charges moving paraxially outside a dielectric cylindrical waveguide
摘要：
本文研究了带电粒子在平行于圆柱轴线的介质柱外运动时产生的辐射。假设圆柱体浸入均匀介质中。给出了矢势、电场和磁场的表达式。研究了三种辐射的谱分布：（i）外部介质中的切伦科夫辐射（CR），（ii）介质柱导模上的辐射，和（iii）表面极化激元的发射。与前两种辐射不同，表面极化激元的产生没有速度阈值。相应的辐射存在于光谱范围内，其中圆柱体和周围介质的介电常数具有相反的符号。发射的表面极化激元的光谱范围随着粒子能量的减小而变窄。的一般结果示出了一个特殊的情况下的Drude模型的圆柱体的介电常数的色散。我们表明，圆柱体的存在下，可能会导致出现强窄峰的光谱分布中的CR在外部介质。指定了这些峰出现的条件，并分析估计了相应的高度和宽度。讨论了粒子在聚束中的集体效应。
英文摘要：
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.
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