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

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

Binarity in Cool Asymptotic Giant Branch Stars: A Galex Search for Ultraviolet Excesse

The search for binarity in AGB stars is of critical importance for our understanding of how planetary nebulae acquire the dazzling variety of aspherical shapes which characterises this class. However, detecting binary companions in such stars has been severely hampered due to their extreme luminosities and pulsations. We have carried out a small imaging survey of AGB stars in ultraviolet light (using GALEX) where these cool objects are very faint, in order to search for hotter companions. We report the discovery of significant far-ultraviolet excesses towards nine of these stars. The far-ultraviolet excess most likely results either directly from the presence of a hot binary companion, or indirectly from a hot accretion disk around the companion.Comment: revised for Astrophysical Journa

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

Therapeutic drug monitoring of itraconazole and the relevance of pharmacokinetic interactions

ABSTRACTA review of the pharmacological aspects of greatest relevance in relation to the monitoring of itraconazole serum levels is presented in this article. The main causes of pharmacokinetic variability, e.g., poor aqueous solubility, the presystemic first-pass effect with the involvement of transporters such as P-glycoprotein, the high extent of metabolism mediated by the CYP450 system and a high probability of pharmacological interactions, are documented and discussed. The pharmacokinetic–pharmacodynamic criteria used to optimise antibiotic therapy, as well as their application to antifungal drugs, are also discussed. Data concerning the breakpoints established for the minimum serum concentrations of itraconazole are included, and the most relevant justifications for drug monitoring are cited

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