Giuseppe Schettini

Generalized Bessel-Gauss beams

In this paper we describe a superposition model for Bessel-Gauss beams, in which higher orders are included. An analogous model leads to a different class of beams, namely the modified Bessel-Gauss beams. Then a generalized set of beams, containing the previous beams as particular cases, is introduced. The behaviour of these beams upon propagation is investigated, both analytically and numerically.

Plane-wave scattering by a perfectly conducting circular cylinder near a plane surface: cylindrical-wave approach

A new method for the analysis of the diffraction of a plane wave impinging on a perfectly conducting circular cylinder in front of a generally reflecting surface is presented. The surface is characterized by its complex reflection coefficient, enabling us to treat a wide class of reflecting surfaces. The presence of the surface is taken into account by means of a suitable expansion of the reflected field in terms of cylindrical functions. The method gives the solution of the scattering problem in both the near and the far field regardless of the polarization state of the incident field. Numerical examples for dielectric interfaces are presented, and comparisons are made with results presented in the literature.

Plane wave expansion of cylidrical functions

Abstract Cylindrical waves, i.e. the product of a Hankel function of integer order times a sinusoidal angular factor, often occur in diffraction theory. We derive the expansion of a cylindrical wave into plane waves and we give some examples of applications.

Current drive at plasma densities required for thermonuclear reactors

Progress in thermonuclear fusion energy research based on deuterium plasmas magnetically confined in toroidal tokamak devices requires the development of efficient current drive methods. Previous experiments have shown that plasma current can be driven effectively by externally launched radio frequency power coupled to lower hybrid plasma waves. However, at the high plasma densities required for fusion power plants, the coupled radio frequency power does not penetrate into the plasma core, possibly because of strong wave interactions with the plasma edge. Here we show experiments performed on FTU (Frascati Tokamak Upgrade) based on theoretical predictions that nonlinear interactions diminish when the peripheral plasma electron temperature is high, allowing significant wave penetration at high density. The results show that the coupled radio frequency power can penetrate into high-density plasmas due to weaker plasma edge effects, thus extending the effective range of lower hybrid current drive towards the domain relevant for fusion reactors.

Comments on "Scattering by a finite set of perfectly conducting cylinders buried in a dielectric half-space: a spectral-domain solution

An analytical-numerical technique, for the solution of the two-dimensional electromagnetic plane-wave scattering by a finite set of perfectly conducting circular cylinders buried in a dielectric half-space, is presented. The problem is solved for both the near- and the far-field regions, for TM and TE polarizations. The diffracted field is represented in terms of a superposition of cylindrical waves and use is made of the plane-wave spectrum to take into account the reflection and transmission of such waves by the interface. The validity of the approach is confirmed by comparisons with results available in the literature, with very good agreement. The multiple interactions between two buried cylinders have been studied by considering both the induced currents and the scattered field diagrams. Applications of the method to objects of arbitrary cross-section simulated by a suitable configuration of circular cylinders are shown.

Scattering by buried dielectric cylindrical structures

[1] An analytical-numerical technique for the solution of the two-dimensional electromagnetic plane wave scattering by a finite set of dielectric circular cylinders buried in a dielectric half-space is presented. The problem is solved for both the near- and far-field regions, for transverse magnetic and transverse electric polarizations. The scattered field is represented in terms of a superposition of cylindrical waves, and use is made of the plane wave spectrum to take into account the reflection and transmission of such waves by the interface. The validity of the approach is confirmed by comparisons with results available in the literature, with very good agreement, and by self-consistency tests. Applications of the method to objects of arbitrary cross section simulated by suitable configurations of circular cylinders are shown.

Plane-wave scattering by a set of perfectly conducting circular cylinders in the presence of a plane surface

A general approach is presented for treating the two-dimensional scattering of a plane wave by an arbitrary configuration of perfectly conducting circular cylinders in front of a plane surface with general reflection properties. The method exploits the angular spectrum representation of cylindrical waves and turns out to be fairly efficient, as demonstrated by a number of examples. Our approach seems promising for several applications both in optics and in microwaves.

Scattering by Perfectly Conducting Circular Cylinders Buried in a Dielectric Slab Through the Cylindrical Wave Approach

An analytical-numerical technique for the solution of the plane-wave scattering problem by a set of perfectly conducting circular cylinders, buried in a dielectric slab, is presented. The problem is solved for both TM and TE polarizations, and for near- and far-field regions. The proposed method expresses the scattered fields in terms of cylindrical waves, and exploits the plane-wave spectrum of a cylindrical function to take into account the reflection and transmission through the planar interfaces. Numerical results are reported and the validity of the approach is confirmed by comparison with results given in the literature, showing a good agreement.

Scattering by a Circular Cylinder Buried Under a Slightly Rough Surface: The Cylindrical-Wave Approach

An analytical-numerical technique for the scattering problem of a plane wave by a cylinder buried under a rough surface, based on the Cylindrical Wave Approach, is presented. The rough deviations on the interface are dealt with by means of the Small Perturbation Method. Reflection and transmission coefficients are evaluated in a first order approximation, and fields are the sum of a zeroth-order solution, relevant to flat surface, and first-order perturbation fields, associated to the surface roughnesses. Numerical results are obtained through an exact evaluation of the spectral integrals, giving results both in near- and far-field regions, for the case of an interface with sinusoidal profile. The approach is validated through comparisons with the literature, and results showing the effect of geometrical and physical parameters on the scattered field are reported.

Design of a binary grating with subwavelength features that acts as a polarizing beam splitter

A binary diffractive optical element, acting as a polarizing beam splitter, is proposed and analyzed. It behaves like a transmissive blazed grating, working on the first or the second diffraction order, depending on the polarization state of the incident radiation. The grating-phase profile required for both polarization states is obtained by means of suitably sized subwavelength groups etched in an isotropic dielectric medium. A rigorous electromagnetic analysis of the grating is presented, and numerical results concerning its performances in terms of diffraction efficiency as well as frequency and angular bandwidths are provided.