Superscattering of Light from Subwavelength Nanostructures

We provide a theoretical discussion of the scattering cross section of individual subwavelength structures. We show that, in principle, an arbitrarily large total cross section can be achieved, provided that one maximizes contributions from a sufficiently large number of channels. As a numerical demonstration, we present a subwavelength nanorod with a plasmonic-dielectric-plasmonic layer structure, where the scattering cross section far exceeds the single-channel limit, even in the presence of loss.

Figure 1

Total scattering cross section of a nanorod in the lossless case, and the contributions from individual channels. The $m=\pm 1$ channel is near resonant in the plotted frequency range. Its resonant line shape is not apparent since its resonant linewidth is much larger than the frequency range plotted here. (Inset) Schematic of the nanorod. The dark gray and light gray areas correspond to a plasmonic material and a dielectric material, respectively. The geometry parameters are ${\rho }_1=0.3485{\lambda }_p$, ${\rho }_2=0.5623{\lambda }_p$, and ${\rho }_3=0.6370{\lambda }_p$, where ${\lambda }_p=2\pi c/{\omega }_p$, with $c$ being the speed of light in vacuum.

Figure 2

A planar structure. The dark and light gray regions correspond to metal and dielectric material, respectively. $a={\rho }_2-{\rho }_1$, $b={\rho }_3-{\rho }_2$. (Main Figure) The solid lines are the dispersion curves for the structure shown in the inset. The dashed and dotted lines represent the dispersion curves for a corresponding metal-dielectric-metal structure, and the metal-air interface, respectively. The bars represent the properties of the resonance in the scatterer at different angular momentum channels labeled by $m$. The center and the height of each bar correspond to the resonant frequency and the leakage rate, respectively.

Figure 3

Real part of the total field distribution and the Poynting vector lines at the frequency of $0.2542{\omega }_p$ (a) for the nanorod shown in Fig. 1, (b) when the rod is replaced by a same-size uniform plasmonic cylinder. Here the amplitude of an incident plane wave is unity. The white circle at the center indicates the size of the rod.

Figure 4

(a) Total scattering cross section of the nanorod for the lossy case of realistic silver, and the contributions from each individual channel. The $m=\pm 1$ channel is near resonant in the plotted frequency range. Its resonant line shape is not apparent since its resonant linewidth is much larger than the frequency range plotted here. (b) Field distributions and the Poynting vector lines at the frequency $0.2542{\omega }_p$.