Cloaking of Arbitrarily-Shaped Objects with Homogeneous Coatings

We present a theory for the cloaking of arbitrarily-shaped objects and demonstrate electromagnetic scattering-cancellation through designed homogeneous coatings. First, in the small-particle limit, we expand the dipole moment of a coated object in terms of its resonant modes. By zeroing the numerator of the resulting rational function, we accurately predict the permittivity values of the coating layer that abates the total scattered power. Then, we extend the applicability of the method beyond the small-particle limit, deriving the radiation corrections of the scattering-cancellation permittivity within a perturbation approach. Our method permits the design of invisibility cloaks for irregularly-shaped devices such as complex sensors and detectors

Full-wave analytical solution of second-harmonic generation in metal nanospheres

We present a full-wave analytical solution for the problem of second-harmonic generation from spherical nanoparticles. The sources of the second-harmonic radiation are represented through an effective nonlinear polarization. The solution is derived in the framework of the Mie theory by expanding the pump field, the nonlinear sources and the second-harmonic fields in series of spherical vector wave functions. We use the proposed solution for studying the second-harmonic radiation generated from gold nanospheres as function of the pump wavelength and the particle size, in the framework of the Rudnick-Stern model. We demonstrate the importance of high-order multipolar contributions to the second-harmonic radiated power. Moreover, we investigate the p- and s- components of the SH radiation as the Rudnick-Stern parameters change, finding a strong variation. This approach provides a rigorous methodology to understand second-order optical processes in metal nanoparticles, and to design novel nanoplasmonic devices in the nonlinear regime.Comment: 16 pages, 10 figure

Optical gaps, mode patterns and dipole radiation in two-dimensional aperiodic photonic structures

Based on the rigorous generalized Mie theory solution of Maxwell's equations for dielectric cylinders we theoretically investigate the optical properties of two-dimensional deterministic structures based on the Fibonacci, Thue-Morse and Rudin-Shapiro aperiodic sequences. In particular, we investigate band-gap formation and mode localization properties in aperiodic photonic structures based on the accurate calculation of their Local Density of States (LDOS). In addition, we explore the potential of photonic structures based on aperiodic order for the engineering of radiative rates and emission patterns in Erbium-doped silicon-rich nitride photonic structures.Comment: 4 pages with 5 figures (to appear in Physica E, 40, 2008

Observations and modelling of soil slip-debris flow initiation processes in pyroclastic deposits: the Sarno 1998 event

International audiencePyroclastic soils mantling a wide area of the Campanian Apennines are subjected to recurrent instability phenomena. This study analyses the 5 and 6 May 1998 event which affected the Pizzo d'Alvano (Campania, southern Italy). More than 400 slides affecting shallow pyroclastic deposits were triggered by intense and prolonged but not extreme rainfall. Landslides affected the pyroclastic deposits that cover the steep calcareous ridges and are soil slip-debris flows and rapid mudflows. About 30 main channels were deeply scoured by flows which reached the alluvial fans depositing up to 400 000 m3 of material in the piedmont areas. About 75% of the landslides are associated with morphological discontinuities such as limestone cliffs and roads. The sliding surface is located within the pyroclastic cover, generally at the base of a pumice layer. Geotechnical characterisation of pyroclastic deposits has been accomplished by laboratory and in situ tests. Numerical modelling of seepage processes and stability analyses have been run on four simplified models representing different settings observed at the source areas. Seepage modelling showed the formation of pore pressure pulses in pumice layers and the localised increase of pore pressure in correspondence of stratigraphic discontinuities as response to the rainfall event registered between 28 April and 5 May. Numerical modelling provided pore pressure values for stability analyses and pointed out critical conditions where stratigraphic or morphological discontinuities occur. This study excludes the need of a groundwater flow from the underlying bedrock toward the pyroclastic cover for instabilities to occur

The lava flow invasion hazard map at Mount Etna and methods for its dynamic update

This special issue of Annals of Geophysics contains seventeen peer-reviewed papers that cover a wide variety of topics related to the V3-LAVA Project funded by the Italian Dipartimento della Protezione Civile in the framework of the 2007– 2009 Agreement with the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The frequent eruptions of Mount Etna can produce lava flows that can cover distances long enough to invade vulnerable areas on the flanks of the volcano. These require improvements to our forecasting tools for the effective assessment of lava-flow hazards, to help the local authorities to make the necessary decisions during a volcanic eruption. The LAVA Project aims to develop, validate and unify methods for mapping the areas around Etna that are threatened by lava invasion within the next 50 years, and also within the immediate days after an eruption has begun. Both timescales of lava-hazard mapping call for estimations of the probabilities of vent openings – using geological evidence over the long-term, and monitoring data over the short-term

Broadband transmission properties of multilayered structures

The formalism of the scattering matrix is applied to describe the transmission properties of multilayered structures with deep variations of the refractive index and arbitrary arrangements of the layers. We show that there is an exact analytical formula for the transmission spectrum, which is valid for the full spectral range and which contains only a limited number of parameters for structures satisfying the quarter-wave condition. These parameters are related to the poles of the scattering matrix, and we present an efficient algorithm to find them, which is based on considering the ray propagation inside the structure and subsequent application of the harmonic inversion technique. These results are significant to analyze the reshaping of ultrashort pulses in multilayered structures.Comment: 3 pages, 3 figure