Giant field enhancement and resonant wavelength shift through a composite nanostructure

This paper reports a kind of nanostructure composed of a metallic nanosphere pair and a rectangle nanoaperture, which can dramatically enhance the localized optical near-field up to 2100 times larger than the incident optical field. The FEM calculation method was used to investigate the enhancement factors and the coupling effects of different nanostructures. When the composite nanostructures are periodically arranged, the resonance peak can be varied from 560nm to 760nm and the electric field enhancement is about 37 percent larger than that of single composite nanostructure. We attribute these phenomena to two-step confinement of the optical electric field and the coupling effect of the composite nanostructures. Both enhancement factors of single and periodic composite nanostructures are sufficient for single molecule detection.