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

Abstract

Electron beam diffraction radiation sources have the advantages of small size, wavelength tunability, and polarization controllability, showing great application potential in nanophotonic circuits. However, studies on 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 injecting 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.<br>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.<br>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 at the nanoscale, but also lay the foundation for binary information processing and integration in nanophotonic circuits and chiral nano-light-sources in the future.