Strong near field coupling and enhanced energy extraction in metal nanostructures

Summary form only given. Using the principal modes theory [1], we show that the presence of a gold nanodisc (400nm diameter, 35nm thickness) at sub-wavelength distances from a dipole excitation source can result in a larger amount of energy extracted from the electric current in the source and also in greater transmission of light compared to the dipole alone. The enhanced energy extraction from the source is due to the coupling between the excitation source and the backscattered field, as described by Poynting´s theorem [2]. Within the regime of strong interaction we investigate how the disc transports energy to the far field at various system feature wavelengths; the intrinsic resonance of the system (~590nm), the anomalous transmission peak (~610nm) and a reference from the upper steady state of the regime (780nm). We produce images of the disc by scanning the source across the transverse plane, analogous to SNOM imaging which uses simple dipole configurations to model aperture fields [2,3].We find that while the near field of the disc contains light with a wide range of orbital angular momentum modes, the majority of the energy is transported to the far field by just the lower orders. These effects could have useful applications in near field optics and understanding imaging methods such as SNOM.