Validity of classical coupled oscillators model for elucidating surface plasmon effects on optical scattering by silver nanocylinders

Abstract

A study is conducted to examine the possibility of explaining the spectral features TE wave scattered by a single and two silver nanocylinders on the basis of a classical coupled oscillators model. The two oscillators representing the nanocylinder are specified by separate eigen frequencies and damping factors with a coupling constant between them, while the influences of the incoming wave on the oscillators are represented by separate driving forces. The validity of the model is examined by the quality of fitting and its resulted spectral profiles with those calculated from the exact formulation of Mie theory. In the case of a single nanocylinder, excellent fit of [Formula: see text] is found for cylinder radius ranging from 20[Formula: see text]nm to 40[Formula: see text]nm. The best fitted parameters show that the so-called dark oscillator has a narrow spectral profile representing the contribution of surface plasmon resonance while the other so-called bright oscillator has a broad spectral profile that can be associated with the contribution of the slowly-varying scattered background. For scattering by two nanocylinders with separation [Formula: see text], excellent fits are also obtained for wide range of [Formula: see text] from 15[Formula: see text]nm to 100[Formula: see text]nm by introducing Lorentzian-like dispersive coupling between the dark oscillators for both incident light normal and along the axis connecting the cylinders. This study has thus demonstrated the roles of surface plasmon and the plasmonic interactions for the appearance of Fano-like asymmetric cross-section profile.