太赫兹表面极化激元

Terahertz surface polaritons

作为束缚于表面或界面的电磁波与极性元激发的耦合模量子,表面极化激元是克服衍射极限的核心物理.在紫外、可见以及近红外波段,表面等离子极化激元展现出了亚波长特性,具有高分辨成像等应用,并发展成为"表面等离子极化激元亚波长光学"学科;在中红外波段,表面声子极化激元发挥着同样的作用.太赫兹波段曾是人类认识的空白区域,近三十年来得以高速发展,其战略意义重大.具有克服衍射极限能力的太赫兹表面极化激元同样是小型化与集成化太赫兹器件,以及太赫兹超高分辨成像的重要物理基础.近几年来,对以石墨烯为代表的二维材料的研究突飞猛进,诞生了"石墨烯表面等离子极化激元亚波长光学"这门学科,并贡献于太赫兹领域.本文对可在太赫兹波段工作的人工超构材料、掺杂半导体、二维电子气、二维材料、拓扑绝缘体等结构材料的表面极化激元进行了较为全面的总结与介绍,为研制克服衍射极限的太赫兹集成光子学器件提供可资借鉴的物理基础.

Enormous efforts have been made to manipulate the light-matter interactions,especially in sub-diffraction-limited space,leading to miniaturized and integrated photonic devices.In physics,an elementary excitation,called polariton,which is the quantum of the coupled photon and polar elementary excitation wave field,underlies the light-matter interaction.In the dispersion relation,polaritons behave as anti-crossing interacting resonance.Surface polaritons provide ultra-confinement of electromagnetic field at the interface,opening up possibilities for sub-diffraction-limited devices,and various field enhancement effects.In the electromagnetic spectra,terahertz（THz） regime was called THz gap before the 1990 s,but has now been thrust into the limelight with great significance.This review is devoted to the emerging but rapidly developing field of sub-diffraction-limited THz photonics,with an emphasis on the materials and the physics of surface polaritons.A large breadth of different flavours of materials and surface polaritonic modes have been summarized.The former includes metallic,dielectric,semiconductor,two-dimensional（2D） materials,metamaterials,etc.;the latter covers surface phonon-,plasmon-,and hybrid polaritons.In the THz regime,2D surface plasmon polariton and artificial surface phonon polaritons offer more attractive advantages in ability to obtain low-loss,tunable,ultracompact light-matter modes.