基于超构材料的Cherenkov辐射

Cherenkov radiation based on metamaterials

Cherenkov辐射(Cherenkov radiation,CR)是自由电子速度超过介质中光速时产生的电磁辐射,其在粒子探测、生物医学、电磁辐射源等领域具有重要的应用价值.近年来,人们发现由不同材料和结构组成的超构材料具有新奇的力学、声学和光学特性.电磁波在超构材料中的传播、耦合和辐射可以具有与传统材料完全不同的奇特性质.将传统真空电子学与微纳光电子学结合,探索自由电子与超构材料的相互作用,成为近期不少研究者关注的热点之一.超构材料的引入打破了传统材料和结构中电磁学规律的限制,自由电子在其中产生的辐射以及与辐射的相互作用表现出许多新现象和新效应.本文首先回顾了CR的基本概念和辐射原理,在此基础上介绍了自由电子与双曲超材料、负折射率材料、高Q值超材料以及超表面相互作用产生辐射的相关工作,重点阐述在这些不同功能的超构材料中产生CR的机理及其特性,涉及的工作包括无阈值CR、反向CR、受激CR以及辐射偏振和相位的调控.自由电子与各种新型超构材料相互作用的研究和发展,为实现新型高效的集成化自由电子器件提供了新的途径.

Cherenkov radiation(CR)is an electromagnetic radiation emitted by charged particles traveling through a dielectric medium at a speed faster than the phase velocity of light.CR plays an important role in the fields of particle detection,biomedicine and electromagnetic-radiation source.Recently,metamaterials demonstrate their novel mechanical,acoustic,and optical properties by delicately designing the structures and materials.In metamaterials,the electromagnetic properties,such as wave propagation,coupling,and radiation,could be flexibly manipulated.Thus,it is expected that the combination of vacuum electronics and micro-&nanophotonics would result in numerous novel phenomena and effects by having free electrons interacting with metamaterials.In this paper,we firstly review the concept and generation mechanism of CR.Then,recent research advances in the CR generation by using different types of metamaterials are reviewed,including threshold-less CR in hyperbolic metamaterials,reverse CR in negative metamaterials,CR lasing based on high Q-factor metamaterials and Smith-Purcell radiation manipulation with metasurfaces.The unique characteristics and interesting mechanisms of CR based on these metamaterials are elaborated.The research and development of interaction between free electrons and various metamaterials open up possibilities for realizing novel integrated free-electron devices.