Degenerate optical memory effect in dielectric films with randomly rough surfaces

9 págs.; 6 figs.By means of perturbation theory we calculate the angular intensity correlations of linearly polarized electromagnetic waves scattered from a thin dielectric film deposited on a planar perfectly conducting substrate. The illuminated surface is a one-dimensional, randomly rough surface with a power spectrum given either by a Gaussian, or by a rectangle defined to enhance the coupling into guided waves. The dielectric film supports, at least, two guided waves in the absence of the roughness that have distinct wave numbers at the frequency ω of the incident wave. We analyze the angular dependence of the optical memory effect: In addition to its two well known peaks, we demonstrate that, due to degeneracy of the excitation of guided waves, there appear two pairs of peaks symmetrically located about the former absolute maxima at positions related to the difference between the guided wave numbers. This degenerate memory effect is shown to be a multiple scattering effect. ©1997 American Physical SocietyThis work was supported by the Consejo Superior de Investigaciones Científicas and the Dirección General de Investigación Científica y Técnica through Grant No. PB93- 0973-C02-02.Peer Reviewe

Coupling, resonance transmission, and tunneling of surface-plasmon polaritons through metallic gratings of finite length

11 págs.; 10 figs.The Green's-theorem integral equation formulation is employed to study numerically the coupling into surface plasmon polaritons by illuminating a finite metal grating with a Gaussian beam from the vacuum half-space above the metal surface. A flat surface impedance boundary condition is used to simplify the scattering integral equations. The grating coupler period is chosen so that the first diffracted order excites a surface plasmon polariton and the zeroth diffracted order is the only radiating order. In particular, the surface magnetic field and the angular distribution of scattered intensity are calculated. These functions provide in turn the total intensity of the radiation scattered into the vacuum and the total power flow carried by the surface plasmon polariton, from which the energy balance is monitored. In this way, the zeroth order and coupling efficiencies are studied as functions of the angle of incidence θ0 and the grating coupler height sc, with the aim of analyzing the influence of the length of the illuminated coupler. Our results show that, when the illuminated coupler length is decreased, the photon-surface plasmon polariton coupling resonance broadens as a function of both θ0 and sc, and that larger values of sc. are required to optimize this coupling resonance. In addition, the coupling geometry is exploited to obtain the reflection and transmission coefficients, and the intensity of the scattered volume waves, of a surface plasmon polariton thus excited that impinges on another finite metal grating, called a grating scatterer. Two frequencies of the incoming surface plasmon polariton are considered that lie very close to the lower band edge of the gap in the surface plasmon polariton dispersion relation for the infinite grating scatterer. If the frequency is in the band, a strongly oscillating, resonant behavior of the transmission coefficient as a function of the grating length is obtained. For a frequency in the gap, transmission is negligible unless the grating is short enough that the surface plasmon polariton can tunnel through it. ©1996 American Physical SocietyFinancial support from the Spanish Consejo Superior de Investigaciones Científicas and the Dirección General de Investigación Científica y Técnica (Grant No. PB93- 0973-C02) is acknowledged. This work was supported in part by Army Research Office Grant No. DAAL 03-92-G- 0239.Peer Reviewe

Localized surface-plasmon polaritons in disordered nanostructured metal surfaces: Shape versus Anderson-localized resonances

4 págs.; 5 figs. ; PACS number~s!: 73.20.Mf, 42.25.2p, 68.37.Uv, 78.68.1mThe electromagnetic wave scattering from disordered nanostructured metal surfaces supporting surface-plasmon polaritons (SPP) is studied by means of fully retarded scattering formulations. We investigate the two physical mechanisms which may underlie the excitation of localized SPP: Anderson localization and shape resonances. The former mechanism is discarded since plane-wave excited, localized SPP are observed in the absence of proper Anderson localization of SPP. In contrast, a detailed analysis of the near field for various ensembles of surface realizations permits us to identify SPP shape resonances typically occurring at sub-100-nm grooves or ridges, the latter being significantly stronger. ©2003 American Physical SocietyThis work was supported in part by the Spanish DGIMCyT (Grants Nos. BFM2000-0806 and BFM2001-2265), and by NSF Grant No. INT-0084423.Peer Reviewe

Coupled electric and magnetic dipole formulation for planar arrays of dipolar particles: metasurfaces with various electric and/or magnetic meta-atoms per unit cell

The optical properties of infinite planar array of scattering particles, metasurfaces and metagratings, are attracting special attention lately for their rich phenomenology, including both plasmonic and high-refractive-index dielectric meta-atoms with a variety of electric and magnetic resonant responses. Herein we derive a coupled electric and magnetic dipole (CEMD) analytical formulation to describe the reflection and transmission of such periodic arrays, including specular and diffractive orders, valid in the spectral regimes where only dipolar multipoles are needed. Electric and/or magnetic dipoles with all three orientations arising in turn from a single or various meta-atoms per unit cell are considered. The 2D lattice Green function is rewritten in terms of a 1D (chain) version that fully converges and can be easily calculated. Modes emerging as poles of such lattice Green function can be extracted. This formulation can be applied to investigate a wealth of plasmonic, all-dielectric, and hybrid metasurfaces/metagratings of interest throughout the electromagnetic spectrum.Comment: 8 pages, 4 figure

Competition between Anderson localization and leakage of surface-plasmon polaritons on randomly rough periodic metal surfaces

4 págs.; 2 figs.; 1 tab.The competition between strong localization and radiative damping is studied for surface-plasmon polaritons propagating along a finite, randomly rough metallic surface that is periodic on average, by means of both numerical simulations and perturbation-theoretic calculations. Our results show that localization is the pre-dominant contribution to the exponential decay of the transmission. In addition, it is found that the localization length is larger for a frequency in an allowed band of the surface-plasmon polariton dispersion relation for the underlying periodic structure than it is for a frequency in the vicinity of a gap. No significant leakage inhibition is observed near the band edge. ©1997 American Physical SocietyThis work was supported in part by U.S. ARO Grant No. DAAH 0-96-1-0187 and by both the Spanish DGICYT Grant No. PB93-0973-C02-02 and CSIC. It was also supported by the University of California, Irvine, through an allocation of computer time. J.A.S.-G. acknowledges a travel grant from the Comunidad de Madrid.Peer Reviewe

Light scattering from self-affine fractal silver surfaces with nanoscale cutoff: Far-field and near-field calculations

We study the light scattered from randomly rough, one-dimensional self-affine fractal silver surfaces with nanoscale lower cutoff, illuminated by s- or p-polarized Gaussian beams a few microns wide. By means of rigorous numerical calculations based on the Green theorem integral equation formulation, we obtain both the far- and near-field scattered intensities. The influence of diminishing the fractal lower scale cutoff (from below a hundred, down to a few nanometers) is analyzed in the case of both single realizations and ensemble average magnitudes. For s polarization, variations are small in the far field, being only significant in the higher spatial frequency components of evanescent character in the near field. In the case of p polarization, however, the nanoscale cutoff has remarkable effects stemming from the roughness-induced excitation of surface-plasmon polaritons. In the far field, the effect is noticed both in the speckle pattern variation and in the decrease of the total reflected energy upon ensemble averaging, due to increased absorption. In the near field, more efficient excitation of localized optical modes is achieved with smaller cutoff, which in turn leads to huge surface electric field enhancements.Comment: REVTeX 4, 10 page

Near-field and far-field scattering of surface plasmon polaritons by one-dimensional surface defects

9 págs.; 9 figs.; 1 apéndiceA rigorous formulation for the scattering of surface plasmon polaritons (SPP's) from a one-dimensional surface defect of any shape that yields the electromagnetic field in the vacuum half-space above the vacuum-metal interface is developed by the use of an impedance boundary condition. The electric and magnetic near fields, the angular distribution of the far-field radiation into vacuum due to SPP-photon coupling, and the SPP reflection and transmission coefficients are calculated by numerically solving the k-space integral equation upon which the formulation is based. In particular, we consider Gaussian-shaped defects (either protuberances or indentations) and study the dependence of the above-mentioned physical quantities on their 1/e half-width a and height h. SPP reflection is significant for narrow defects (a ≲ λ/5, for either protuberances or indentations, where λ is the wavelength of the SPP); maximum reflection (plasmon mirrors) is achieved for a ≈ λ/10. For increasing defect widths, protuberances and indentations behave differently. The former give rise to a monotonic increase of radiation at the expense of SPP transmission for increasing defect half-width. However, indentations exhibit a significant increase of radiation (decrease of SPP transmission) for half-widths of the order of or smaller than the wavelength, but tend to total SPP transmission in an oscillatory manner upon further increasing the half-width. Both the position of the maximum radiation and the oscillation period depend on the defect height, which in all other cases only affects the process quantitatively. Light emitters might thus be associated with either wide indentations or protuberances with widths that are of the order of or smaller than the wavelength. ©1999 The American Physical Society.This work was supported in part by Army Research Office Grant No. DAAH 0-96-1-0187, and by both the Spanish DGES (Grants No. PB96-0844-C02-02 and PB97-1221) and the Consejo Superior de Investigaciones Científicas.Peer Reviewe

Enhanced long-range correlations of coherent waves reflected from disordered media

4 págs.; 3 figs.We study the intensity angular correlation function of scalar waves, scattered on reflection from disordered media, for the case in which the sample is so small that the speckle pattern does not follow a joint Gaussian statistics, and thus the factorization approximation does not hold. An enhanced long-range correlation is predicted that exhibits two peaks due to coherent effects analogous to those producing the phenomenon of enhanced backscattering of the mean intensity as a result of time-reversal symmetry. © 1992 The American Physical Society.This work was supported by the CICYT under Grant No. PB0278. J.A.S.-G. acknowledges a grant from the MEC.Peer Reviewe

Thermal switching of the scattering coefficients of terahertz surface plasmon polaritons impinging on a finite array of subwavelength grooves on semiconductor surfaces

8 págs.; 8 figs.; 1 tab. ; PACS number s : 73.20.Mf, 78.68. m, 65.40. b, 41.20.JbWe present a theoretical framework that allows us to investigate the scattering of terahertz surface plasmon polaritons (SPP's) by arrays of subwavelength grooves and ridges on semiconductors. The formulation is based on the reduced Rayleigh equation resulting upon imposing an impedance boundary condition. Guided by approximate estimations of the broadening with temperature of the first gap in the SPP dispersion relation in the case of indium antimonide samples with rectangular grooves, numerical calculations are carried out to determine the spectral dependence of all the SPP scattering channels (reflection, transmission, and radiation) in the immediate vicinity of that gap. The thermally induced switching of the SPP reflection and transmission nearby the lower SPP band edge is investigated as a function of groove parameters (size and number); near-field intensity maps are also presented. We thus shed light on the SPP scattering and switching physical mechanisms, thereby providing the most suitable experimental configurations. © 2006 The American Physical Society.This work was supported in part by the Spanish “Ministerio de Educación y Ciencia” Grant Nos. BFM2003-0427 and FIS2004-0108 and “Comunidad de Madrid” Grant MICROSERES and by the European Union Grant HPRN-CT- 2002-00206. The work of J.G.R. was supported by the “Stichting voor Fundamenteel Onderzoek der Materie” FOM, which is financially supported by the “Nederlandse Organisatie voor Wetenschappelijk Onderzoek” NWO.Peer Reviewe

Near-field electromagnetic wave scattering from random self-affine fractal metal surfaces: Spectral dependence of local field enhancements and their statistics in connection with surface-enhanced Raman scattering

11 págs.; 10 figs.By means of rigorous numerical simulation calculations based on the Green's theorem integral equation formulation, we study the near electromagnetic field in the vicinity of very rough, one-dimensional self-affine fractal surfaces of Ag, Au, and Cu (for both vacuum and water propagating media) illuminated by a p-polarized field. Strongly localized enhanced optical excitations (hot spots) are found, with electric field intensity enhancements of close to 4 orders of magnitude and widths below a tenth of the incoming wavelength. These effects are produced by the roughness-induced surface-plasmon polariton excitation. We study the characteristics of these optical excitations as well as other properties of the surface electromagnetic field, such as its statistics (probability density function, average, and fluctuations), and their dependence on the excitation spectrum (in the visible and near-infrared regions). Our study is relevant to the use of self-affine fractals as surface-enhanced Raman scattering substrates, where large local and average field enhancements are desired. ©2000 American Physical SocietyThis work was supported by the Spanish Dirección General de Ensenñanza Superior e Investigación Científica y Técnica, through Grant No. PB97-1221. We also thank the Mexican-Spanish CONACYT-CSIC program for partial travel support.Peer Reviewe