Surface polaritons of small coated cylinders illuminated by normal incident TM and TE plane waves.

The surface polariton properties of TM or TE plane wave scattered by a coated cylinder are investigated in this paper. The coated cylinder (whose outer radius is much smaller than the wavelength) is assumed to be electrically small and low dissipative. Analytical formulas of the plasmonic resonances are derived and found to agree well with those obtained from exact expressions in the classical scattering theory. The behaviors of the scattering coefficients at resonances are also discussed and compared for different cases. While a single cylinder has the resonance at the relative permittivity of epsilon(r) = -1 (or relative permeability of mu(r) = -1) for the TE (or TM) polarization, the resonances of the coated cylinders change with different n values (where n denotes the series term or mode of the field), and also the inner and outer radii. It is shown that the scattered field in the near zone can be enhanced significantly compared to the incident wave. For the TE incident case, we take a silver coated nano-cylinder as an example to illuminate the near-field optical effect. Also, we have studied the peak values of the nth order scattered field for different n values and electrical parameter k0b (where k0 is the wavenumber of the free space and b denotes the outer radius of the cylinder) around the cylinder. The derived new formulas for total cross sections are given and they may provide us with some potential photonic applications such as surface cleaning and etching.