An extended method based on the long-wavelength approximations is introduced to investigate the optical properties of finite-size metal nanopillars for different incident light polarizations. In this proposed method, the optical depolarization factors are the key parameters and strongly depend on the position of the considered point dipole inside the irregular-shaped nanoparticles. Interestingly, depending on the polarization, it is shown that the conventional point dipole positioned at the center of a nonspherical nanoparticle seldom is the proper choice as its simple electromagnetic model. The adequate off-center point, though, is determined and physically associated with the electric-field distribution inside the nanoparticle, which is supported by numerical computations. Remarkably, the proposed extended MLWA could extend the quasi-static limits and, consequently, more accurately predict the optical properties of the finite-size plasmonic nanopillar. (C) 2016 Optical Society of America
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