等腰直角三角形光阱中的电子束手性衍射辐射

Electron beam chiral diffraction radiation in isosceles right triangle light-well

电子束衍射辐射源具有体积小、波长可调和极化可控等优点,在纳米光子电路中显示出巨大的应用潜力.这里展示了等腰直角三角形光阱纳米结构中电子束衍射辐射的光学手性现象,可以获得手性度高于40%的衍射辐射信号,光学手性的状态能被有效调控,甚至可以实现手性的反转.通过详细分析体系中的真空电磁模式和电荷分布的动态变化,为这种手性光学效应的产生提供合理的理论解释.电子束激发源所具有的纳米尺度下聚焦和移动的优势使电子束衍射辐射的光学手性具有灵活的调节潜力.本文提出的物理机制和独特的实验平台对于未来二进制纳米光子电路和手性纳米光源的发展具有重要意义.

Electron beam diffraction radiation source has the advantages of small size,wavelength tunability,and polarization controllability,showing great potential applications in nanophotonic circuits.However,studies of optical chirality of electron beam diffraction radiation are relatively scarce.The optical chirality of electron beam diffraction radiation in isosceles right triangle light-well is realized and demonstrated in this work.The light-well consists of twelve alternating layers of gold and silicon dioxide,and the electron beam diffraction radiation originates from oscillating dipole sources within the light-well.In the case of the electron beam injected at the geometrically asymmetric position within the structure,the diffraction radiation signal with a maximum chirality of more than 40%can be obtained.By changing the injection position of the electron beam,the state of the optical chirality can be effectively controlled,and even the inversion of the chirality can be realized.By analyzing the vacuum electromagnetic mode in the system and the dynamic evolution of charge distribution in the gold layer,a reasonable theoretical explanation is provided for the generation of the chiral optical effect.A semi-analytical model for explaining the optical chirality of electron beam diffraction radiation is given by solving the incident electromagnetic field and the waveguide modes in the light-well.The observed difference between left-handed circularly polarized and right-handed circularly polarized signals originates from the asymmetry between left-handed and right-handed electromagnetic modes in the light-well caused by the geometrically asymmetric positional excitation,which ultimately leads to far-field chiral radiation determined by the electromagnetic field within the light-well.In addition,the simulation results of the surface charge distribution of the top gold film of the light-well reveal the correlation between the dynamic evolution of the surface charge distribution and the radiation chirality.The advantages of nanoscale focusing and moving of electron beam excitation source make the optical chirality of electron beam diffraction radiation have more flexible adjustment potential.The proposed physical mechanism and unique experimental platform not only provide new ideas for manipulating optical chirality on a nanoscale,but also lay the foundation for binary information processing and integration in nanophotonic circuits and chiral nano-light-sources in the future.