Sorting transverse and longitudinal plasmonic fields by a structure of metal-nanoparticle-on-film

Surface plasmon polaritons (SPPs) play an important role in modern nanophotonics due to their vectorial characteristics, subwavelength scale and field enhancement natures. Up to now, a great deal of advanced scheme has been proposed to character the intensity distributions of SPPs, it remains challenging to achieve the measurement of the transverse and longitudinal fields of SPPs simultaneously with the NSOM probe. Here, we develop a technique for sorting the transverse and longitudinal field distributions of SPPs simultaneously with a metal-nanoparticle-on-film structure. The metal-nanoparticle-on-film structure was introduced as a near-field probe to couple the SPPs fields signals into far-field, of which the angular distribution is intensely polarization correlation. The imaging of the transverse and longitudinal fields with high precision can be achieved by collecting and analyzing the scattering signals which are caused by the horizontal and perpendicular polarization. The idea was validated theoretically by characterizing a complex SPPs field with the finite difference time-domain (FDTD) method. The proposed method realizes transverse and longitudinal field sorting of SPP field, and is conducive to the further study of the physical properties of SPP fields, for instance transverse spin, spin-orbit interaction, etc.