Resonance Wavelength Dependence and Mode Formation in Gold Nanorod Optical Antennas with Finite Thickness

In this paper we analyze the dependence of the resonance wavelength and mode formation of an optical gold nanorod antenna on its geometrical parameters in the wavelength range 500-1400 nm. In particular, we prove that nanoantennas differ from RF counterparts, since the minima and maxima, i.e., nodes and anti-nodes, of the resonant modes do not go to zero and show very intense peak at the corners due to non-negligible thickness. Moreover, FDTD simulations reveal that the usually considered linear relation between the resonant wavelength and the nanorod length has to be modified when the nanorod thickness is taken into account.