Controllable chiral emissions from free-electron driven plasmonic metasurfaces

Arbitrary control of the light emission in nanoscale is of great importance to high-performance, compact and integrated on-chip systems. Free-electron impact interactions with metasurfaces provide an excellent platform for the realization of a point source while the generation and engineering of chiral polarized emission is still unresolved. In this work, we propose a method to flexibly generate and control the chiral emission to the desired direction at specified wavelength(s) with plasmonic chiral metasurfaces. Emission chirality dependences on the impacting positions and wavelength are demonstrated. The same chirality is achieved within a broad bandwidth from 750 nm to 1100 nm at a fixed impacting position. Additionally, we also illustrate a specified wavelength at which the chirality is insensitive to the impacting positions. Simulated far field intensity distributions confirm the approach to implement different chiral emissions. To solve the divergent distributions at chirality 0, we also propose an anisotropic metasurface to confine the left circular polarized and right circular polarized lights in a tight solid angle. The competition between the chiral emission enhancement and ohmic loss on the nanoparticles number is also investigated. Our work promises effective manipulation of the chiral emissions and may find applications in quantum communication and biomolecule detections.