Abstract
We present a new effective permittivity (EP) model to accurately calculate surface plasmons (SPs) using the finite-difference time-domain (FDTD) method. The computational representation of physical structures with curved interfaces causes inherent errors in FDTD calculations, especially when the numerical grid is coarse. Conventional EP models improve the errors, but they are not effective for SPs because the SP resonance condition determined by the original permittivity is changed by the interpolated EP values. We perform FDTD simulations using the proposed model for an infinitely-long silver cylinder and gold sphere, and the results are compared with Mie theory. Our model gives better accuracy than the conventional staircase and EP models for SPs.
Highlights
Surface plasmons (SPs) are waves that propagate along the surface of a metal and play a role in subwavelength imaging [1]
We have proposed a S-effective permittivity (EP) model for finite-difference time-domain (FDTD) computation of plasmonic materials
The S-EP model is a modification of the EP model derived from Ampere’s law
Summary
Surface plasmons (SPs) are waves that propagate along the surface of a metal and play a role in subwavelength imaging [1]. A different approach using effective permittivities (EPs), which derives from interface interpolations based on Ampere’s and Faraday’s integration laws, can reduce the error of the permittivity model on coarse grids in a simple implementation and at low computational cost [23,24,25,26,27,28,29,30,31,32,33,34,35]. Plasmonic waveguides have been analyzed by the conformal FDTD method using EPs [36], but the SP resonance wavelength is shifted several nanometers even on a fine grid (wavelength/grid spacing = 60) This method involves a complicated implementation given by a fourth-order differential equation.
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