Optical resonances on sub-wavelength silver lamellar gratings

Abstract

The optical response of sub-wavelength silver lamellar gratings has been theoretically investigated. Two distinct types of resonance have been predicted for incident radiation with E-field perpendicular to the long axis of the wires. The first resonance has been identified as a cavity mode resonance that is associated with transmission enhancement. The second resonance has been identified as an entirely new horizontal plasmon resonance on the incident (and transmission) surfaces of the wires of the grating. Normal surface plasmon modes are investigated on discontinuous gratings, and their relation to those found on continuous gratings is highlighted by focusing on the perturbation effect of the discontinuities. It is shown that the new horizontal plasmon mode is in no way related to the well known diffractively coupled surface plasmon, and is shown to have a particle plasmon-like nature. It is therefore termed a horizontal particle plasmon, and may be either an uncoupled horizontal particle plasmon resonance (a 1-dimensional particle plasmon) or a coupled horizontal particle plasmon resonance (a 2-dimensional particle plasmon) depending on the height of the grating. It is shown that this resonance may result in a reflection efficiency that is very high, even when the grating would be optically thin if it were a homogeneous film, therefore, it behaves as an inverse wire grid polariser as it reflects more TM than TE incident radiation.

Surface plasmon polaritons on deep, narrow-ridged rectangular gratings

“…For cavity modes in a single groove in a perfect conductor, it has been shown that end effects lead to a decrease in frequency as the groove is broadened [20]. However, it has been discussed elsewhere [21] that, for very narrow grooves in a finite conductor, as the groove is broadened there is an increase in frequency of the cavity mode due to the finite conductivity, and that in the optical regime, this effect dominates [22]. It is therefore expected that cavity modes, on the structure presented here, will increase in frequency as the grooves are broadened, and furthermore, that the resonance will broaden and diminish.…”

Modeling of Plasmon Resonances of Multiple Flat Noble-Metal Nanostrips With a Median-Line Integral Equation Technique

“…The discrepancy between two curves is less than 5% in the studied range. In fact, our results may be more accurate than those of [3]- [7] as our algorithm's convergence has been proven theoretically (see for details [19]) while the specific forms of the IE used in [3]- [7] do not amend themselves for such a mathematical proof. Here, we understand the convergence in mathematical sense, as possibility of reducing the error of computations by solving progressively larger matrices (many divergent schemes still yield a few correct digits in solution).…”

Finite gratings of many thin silver nanostrips: Optical resonances and role of periodicity

“…This is caused by the effects of extraordinarily large reflection, transmission, emission, and near-field enhancement that have been found in the scattering of light by periodic scatterers. [9][10][11][12] More broadly, these resonances display a variety of Fano shapes near so-called Rayleigh anomalies of associated infinite grating. 10,13,14 Much controversy still exists around these resonances.…”

“…waveguide-mode) resonances or "vertical plasmons" observable on the thick strip metal gratings. 11,[33][34][35][36] In the reminder of this paper, Section II presents concise summary of the formulation and method of treatment. Section III deals with numerical study of resonances in the case of H-polarization.…”