Role of radiation and surface plasmon polaritons in the optical interactions between a nano-slit and a nano-groove on a metal surface.

Through full-vectorial simulations and analytical models, we investigate the role of radiation and surface plasmon polaritons (SPP) in the optical interaction between a nano-slit and a parallel nano-groove on a metal surface. We quantitatively confirm the radiaton as the interaction mechanism in perfect electrical conductors (PEC), and verify the role of radiation and SPP in the slit-groove interaction in silver. While the contribution of SPP dominates for the nano-slit and nano-groove placed far apart, the radiation plays a significant role for the nano-slit and nano-groove with smaller separations comparable to one wavelength. We present the first quantitative of the individual contributions of the radiation and SPP on the transmission through the nano-slit.