Refined Model for Plasmon Ruler Based on Catenary-Shaped Optical Fields

The catenary, in addition to be one intriguing structure in mechanics and optics, expresses the universal rule of evanescent field coupling between metallic or dielectric nanoparticle pairs. In the present paper, the catenary-shaped optical field distributions within the gap of nanoparticle pairs as well as the distance dependence of scattering spectrum shift are investigated. A novel model defined by power attenuation functions is established to describe the scaling behavior of local field enhancement and plasmon wavelength shift of metallic nanoparticle pairs. Compared with traditional model, the proposed model can more accurately describe the scaling behavior of scattering spectrum shift, which help to refine the existing plasmon rulers. Our findings can serve as a guideline for designing and optimizing catenary-field-based plasmon rulers.