基于电子共振跃迁的光频本征型超常电磁介质

Intrinsic abnormal electromagnetic media at optical frequencies based on resonant transitions of electrons

超常电磁介质因其异于普通材料的电磁性质而受到广泛关注,基于周期性谐振结构的超常介质(即超材料)到光频段以后会出现加工困难,且损耗明显,而基于材料本征性质的超常介质却表现出独特的优势.文章简要介绍了三类本征型超常电磁介质的形成机制,它们分别是强各向异性机制、自旋波和等离子体耦合机制以及电子共振跃迁机制.重点介绍了基于电子共振跃迁的超常介质.采用半经典理论分析了气态介质中二能级、三能级体系的电偶极跃迁和磁偶极跃迁过程,总结了极化率和磁化率的一般表达式,综述了基于二能级、三能级及多能级模型获得的气态超常电磁介质.此外,对凝聚态体系中的电子共振跃迁和超常电磁性质关系作了简要阐述.最后,对采用实验方法实现的这种本征型超常电磁介质进行了简要分析.

Abnormal electromagnetic media have attracted extensive attention due to their novel electro- magnetic properties in comparison with ordinary materials. Abnormal media based on periodic resonant structures （metamaterials） have the disadvantages of complicated fabrication and high loss at optical frequencies, while media based on the intrinsic properties of natural materials exhibit distinct advantages. In this paper, the mechanisms of three kinds of intrinsic abnormal electromagnetic media are described： strong anisotropy, the coupling between spin-waves and plasma, and the resonant transitions of electrons; the third is discussed in detail. Semi-classical theory is used to analyze the electric and magnetic dipole tran- sitions in a gas medium with two or more energy levels, and the expressions for the polarizability, magnetic susceptibility, and abnormal electromagnetic properties in these models are presented. In addition, the relationships between the electronic resonant transitions and extraordinary electromagnetic properties in condensed matter are outlined. Finally, a brief analysis of how to achieve this type of intrinsic abnormal medium experimentally is given.