Mapping the weak plasmonic transverse field by a dielectric-nanoparticle-on-film structure with ultra-high precision

Highly confined electromagnetic fields play a significant role in modern nano-optics, among which surface plasmon polaritons (SPPs) are outstanding because of their subwavelength and enhancement nature. While many state-of-the-art methods have been proposed to uncover the field distribution of SPPs, it still faces challenge to map the weak transverse field component (the field tangential to the interface) of SPPs with high contrast and precision. We propose a direct imaging technique, which employs a dielectric-nanoparticle-on-metal-film (DNP-MF) structure as a near-field probe, to overcome this difficulty. The angular distribution of the scattering radiation from the structure is strongly polarization dependent. By extracting the scattering signals that are mainly induced by the horizontal polarization, the imaging of the weak plasmonic transverse field with high precision can be achieved. The mappings of SPPs distributions excited by various vector beams were performed in experiment, which accord excellent with theory. This technique provides a new approach for near-field imaging with high contrast and reliability, which is expected to be valuable for studying the vectorial features of SPPs such as transverse spin, spin-orbit interactions, etc.