Controllable and switchable chiral near-fields in symmetric graphene metasurfaces

A strong chiral near-field plays significant roles in the detection,separation and sensing of chiral molecules.In this paper,a simple and symmetric metasurface is proposed to generate strong chiral near-fields with both circularly polarized light and linearly polarized light illuminations in the mid-infrared region.Owing to the near-field interaction between plasmonic resonant modes of two nanosheets excited by circularly polarized light,there is a strong single-handed chiral near-field in the gap between the two graphene nanosheets and the maximum enhancement of the optical chirality could reach two orders of magnitude.As expected,the intensity and the response wavelength of the chiral near-fields could be controlled by the Fermi level and geometrical parameters of the graphene nanosheets,as well as the permittivity of the substrate.Meanwhile,based on the interaction between the incident field and scattered field,the one-handed chiral nearfield in the gap also could be generated by the linearly polarized light excitation.For the two cases,the handedness of the chiral near-field could be switched by the polarized direction of the incident light.These results have potential opportunities for applications in molecular detection and sensing.

Nanowire-supported plasmonic waveguide for remote excitation of surface-enhanced Raman scattering

Due to its amazing ability to manipulate light at the nanoscale,plasmonics has become one of the most interesting topics in the field of light–matter interaction.As a promising application of plasmonics,surface-enhanced Raman scattering(SERS)has been widely used in scientific investigations and material analysis.The large enhanced Raman signals are mainly caused by the extremely enhanced electromagnetic field that results from localized surface plasmon polaritons.Recently,a novel SERS technology called remote SERS has been reported,combining both localized surface plasmon polaritons and propagating surface plasmon polaritons(PSPPs,or called plasmonic waveguide),which may be found in prominent applications in special circumstances compared to traditional local SERS.In this article,we review the mechanism of remote SERS and its development since it was first reported in 2009.Various remote metal systems based on plasmonic waveguides,such as nanoparticle–nanowire systems,single nanowire systems,crossed nanowire systems and nanowire dimer systems,are introduced,and recent novel applications,such as sensors,plasmon-driven surface-catalyzed reactions and Raman optical activity,are also presented.Furthermore,studies of remote SERS in dielectric and organic systems based on dielectric waveguides remind us that this useful technology has additional,tremendous application prospects that have not been realized in metal systems.