Enhanced near-field distribution inside substrates mediated with gold particle: optical vortex and bifurcation

Abstract

We present the numerical results of the near-field enhancement inside a substrate mediated with a gold particle for nanohole processing on dielectric and semiconductor materials. The numerical calculation is done with the Finite-Difference Time-Domain (FDTD) method. Our results show that the near-field distribution inside the substrate shows quite unique properties, different from those on the substrate. The presence of a substrate results in a significant shift of the resonant wavelength where a maximal field enhancement is achieved. The depth profile of the enhanced near-field will predict the depth profile of the nanohole processing. The optical vortex and bifurcation are observed in the strongly enhanced area inside the substrate. This is similar to a phenomenon predicted near the plasmon resonant conditions. Similar optical bifurcation and vortex patterns are observed inside different substrates at the optimal wavelength excitation. The resonant wavelength shift is found to be strongly dependent on the refractive index of the substrate. These results are not explainable only by an image charge effect.