Plasmonic excitations in metallic nanoparticles: Resonances, dispersion characteristics and near-field patterns

Abstract

Metamaterials acquire their functionality from the structuring of the small building blocks, "artificial atoms". Our paper provides a study of the resonant behaviour for a variety of metallic nanoparticles in the region of hundreds of THz. Resonant modes for nanorods of rectangular cross section are investigated numerically for different types of excitation and the set of resonant frequencies (fundamental and higher order) are determined for rods of various length. From that the dispersion relationship for surface plasmon-polaritons propagating along the rod is deduced. We analyse resonant-mode near-field distribution of the electric field, including the field lines, to emphasise the underlying physics. Resonant frequencies are also found and field distributions analysed when the rods are combined to form particles of L, U and O shapes. The similarities and differences between those particles, both in the values and in the number of resonances, are discussed. The results of this study may aid the design of nanostructured metamaterials with required properties in the IR and optical domain.

Selective excitation of bright and dark plasmonic resonances of single gold nanorods

“…The resonance lengths (100 and 380 nm) correspond to the first (m=1) and third (m=3) order plasmonic modes since E x presents respectively one and three field maxima inside the nanorods (the m index is the ratio between the nanorod length and the effective wavelength as described below in the Fabry Perot description of resonances). However, as a change of sign in the E x distribution corresponds to a π-phase change, these odd modes present two π-phase changes at their extremities, as previously reported [31]. The Coupled Mode Theory proposed by A. Yariv [32] says that optical modes are efficiently excited when the excitation intensity and phase spatial profiles match with those of the latter optical modes.…”

Directly patterned substrate-free plasmonic “nanograter” structures with unusual Fano resonances

“…As clearly shown in Figure 3d and 3e, the ''broad'' resonance can be attributed to the EOT background continuum from the array of MHs. However, the ''narrow'' resonance appears to be unexpected because the SRRs would not support any resonance under such an unconventional excitation scheme in the absence of MHs 36,40 , indicating the unusual nature of the observed Fano resonances. To identify the mechanism underlying the observed Fano resonance behavior, U-type nanograters of MH-VSRR arrays with various heights h, i.e., the vertical U-arm length, were fabricated and investigated.…”

“…Conventionally, the resonances of an SRR can be excited by incident light with the electric field (E) polarized parallel to the U-plane (for instance, along the x-direction as shown in Figure 3a) or, alternatively, with the magnetic field perpendicular to the U-plane 36,40 . Therefore, in SRRs reported thus far, including planar 36,40 , vertical 41,42 , and multilayered 3,14 SRR structures, an unconventional excitation scheme in which the electric field is polarized perpendicular to the U-plane in the y-direction would normally induce no electromagnetic resonance and hence has usually remained unexplored. Here, we demonstrate that under such unconventional excitation of the MH-VSRRs, the integration of SRRs significantly changes the extraordinary optical transmission (EOT) 43 properties of the original MH arrays.…”

Faced folded rods as nano-antenna for optical devices

“…In this paper, in order to construct more hot spots, two single folded rods are faced each other. The quasi-static approximation for electromagnetics is valid when the size of nanostructure is smaller than the free space wavelength of the incident light 15,16,17 . The entire structure is illuminated with a uniform electric field at any instant of time.…”