Luiz G. Guimarães

Analysis of the resonant scattering of light by cylinders at oblique incidence

We study the resonant scattering of light at oblique incidence by dielectric uncoated and coated cylinders. We develop a stable algorithm that permits us to calculate the resonances of a single dielectric cylinder as the tilting angle varies. This algorithm is based on semiclassical formulas for the distance between resonances. Results show that the resonances and the resonant electromagnetic energy flux near and internal to the cylindrical surface are highly sensitive to variations in the tilting angle. In addition, the coating effects are studied for scattering of light at oblique incidence by an infinite, perfect cylindrical conductor coated by a dielectric layer. In this case the resonance calculations show a peculiar similarity between this light scattering and atomic-molecular scattering. A physical interpretation for these effects is given, based on an analogy of optics and quantum mechanics.

Semiclassical theory to optical resonant modes of a transparent dielectric spheroidal cavity

We study the resonant scattering of light by a transparent dielectric spheroid. We try to understand the features of the resonant modes of a spheroidal optical cavity. In this way, we use an analogy between optics and quantum mechanics. Through this analogy it is possible to interpret resonances as quasibound states of light. Using semiclassical methods such as the WKB method and a uniform asymptotic expansion for spheroidal radial functions, we developed algorithms that permit us to calculate the resonance position as well as the resonance width.

Uniform asymptotic formulae for the spheroidal radial function

This work deals with the problem of the calculation of the radial spheroidal functions. A solution is obtained using uniform asymptotic formulae along with semiclassic methods. The present uniform asymptotic method is based on Olvers theory (Asymptotics and Special Functions, Academic Press, New York, 1974) to asymptotic solutions of the differential equations. Here we show that it is possible to accurately interpolate the spheroidal radial function in the real plane using Airys functions.

Evanescent wave coupling in light scattering of an off-axis normally incident Gaussian beam by two parallel nonabsorbing cylinders.

A theoretical and numerical investigation is devised for resonant light scattering of an off-axis normally incident Gaussian beam by two parallel nonabsorbing cylinders based on the related beam theory developed in J. Opt. Soc. Am. A 14, 640 (1997). By varying the half-beam width, we show that the multireflection process between the two scatterers can be minimized. Moreover, the study is an attempt to understand the underlying physics present in the process of resonance excitation by evanescent wave coupling.

A comparative study in resonant light scattering between spherical and cylindrical dielectric hosts with a metallic inclusion

Abstract We show that dielectric spherical and cylindrical particles contaminated with a metallic inclusion have similar spectral resonant behavior. Both geometries show resonance suppression as the position of the inclusion varies. Moreover, it was theoretically observed that the spherical particle suppresses a resonant mode earlier than the cylindrical one. Based on semi-classical arguments, a physical interpretation of this fact is given. In addition, a comment is also made regarding Wiscombes criteria for estimating the size of the coefficient matrix used to solve the truncated non-homogeneous set of linear equations related to this problem.

Electromagnetic stress on resonant light scattering by a cylinder with an eccentric inclusion

We analyze the resonant scattering of light by a dielectric cylinder with an eccentric cylindrical metallic inclusion. We make efforts to understand the behavior of the electromagnetic (EM) fields and forces inside the dielectric shell as some parameters of the theory vary. To this end, we developed an algorithm for resonant mode calculation and we use an internal multi-reflection ray theory (Debye expansion method) to interpret the resonant and non-resonant contributions to electromagnetic fields as well as the Maxwell stress tensor.

Finite parabolic quantum wells under crossed electric and magnetic fields: a double-quantum-well problem

We show that, in the framework of the effective-mass approximation, an electron confined in a finite parabolic quantum well under crossed electric and magnetic fields can behave as a double-quantum-well system. These homogeneous crossed fields are such that the magnetic field is parallel to the heterostructure layers and the electric field is applied perpendicular to the magnetic field. For a suitable choice of both fields, the electron is confined to a double-quantum-well effective potential.

Narrow resonances and ripple fluctuations in light scattering by a spheroid

We develop a semiclassical theory to explain the rapid ripple fluctuations in the extinction efficiency of light scattering by a transparent prolate spheroid. The theory is based on uniform asymptotic expansion of spheroidal radial functions. We have calculated the extinction efficiency for normal and oblique incidence. Our results suggest that the excitation of resonant electromagnetic modes inside a spheroidal particle is an important factor in the ripple structure. To verify this assumption and based on a Breit-Wigner formula, we develop a method to fit the peaks that appear in the spheroids extinction cross section when some scattering parameters vary. In other words, our calculations suggest that narrow resonances are related to ripple fluctuations, whereas broad resonances contribute to extinction cross-sectional background.

Electronic molecule-like spectrum of quantum wells in crossed fields

Abstract We show that an electron confined to a single finite parabolic quantum well in crossed electric and magnetic fields can behave as a double quantum well system. The magnetic field is parallel to the heterostructure layers and the electric field is perpendicular to those. For a suitable choice of both fields and quantum well width, the electron can be confined to a double quantum well effective potential that is very similar to the electronic potential model for diatomic molecules. The double quantum well spectrum is calculated using a numerical algorithm based on semiclassical methods. A physical interpretation of this quantum system is given based on the analogy to the electrons bound to diatomic molecules.

USE OF RAY TRACING MODELING IN SHALLOW WATER ACOUSTIC SOURCE LOCALIZATION COMBINED WITH MATCHED-FIELD PROCESSING TECHNIQUES

ABSTRACT. Underwater source localization based on acoustic modeling has been a subject of intensive research since a long time. In the case of shallow water scenarios (which are characterized by multilayered bottoms) normal-mode based acoustic propagation models are often combined with Matched-Field Processing techniques in order to provide accurate estimates of both source range and depth. This work discusses the use of a ray tracing model for source localization. Accurate predictions of the acoustic field are obtained by replacing the multilayered bottom with an equivalent (single-layer) bottom, to be used by the ray model, where the properties of the equivalent bottom are obtained through parameter optimization based on the comparison between rays (single-layer) andmodes (multilayer) predictions. The accuracy of this approach is tested using data from an experiment performed by the former Undersea Research Centre of the Supreme Allied Commander Atlantic (SACLANT) in the north of the Elba Island, near the Italian coast. The results indicate that the proposed approach allows a ray model to locate an stationary source with the same accuracy as the one achieved with a normal mode model. Keywords: underwater acoustic modeling, ray-based models, normal mode models. RESUMO. A localizacao de fontes submarinas por meio de modelos de propagacao acustica e um antigo problema de grande interesse cientifico. Em cenarios de aguas rasas, que se caracterizam normalmente por fundos com complexos sistemas multicamadas, os modelos de propagacao baseados na teoria de modos normais sao geralmente combinados com tecnicas de Processamento por Campo Casado para produzirem estimativas acuradas da distância e profundidade de uma fonte acustica. O trabalho aqui apresentado propoe a utilizacao de um modelo de tracado de raios no problema da localizacao. De maneira a produzir estimativas acuradas do campo acustico, o modelo de raios recorre a um modelo equivalente do fundo, baseado numa escolha otima de parâmetros, os quais sao obtidos por meio da comparacao entre as previsoes geradas por um modelo de raios (que considera um ambiente de camada unica) e as geradas por um modelo de modos (que considera um ambiente original multicamadas). A acuracia da metodologia e verificada por meio de dados adquiridos ao norte da Ilha de Elba (nas proximidades da costa italiana), oriundos de um experimento realizado pelo entao Undersea Research Centre of the Supreme Allied Commander Atlantic (SACLANT). Os resultados alcancados indicam que a metodogia aqui proposta demonstra ser possivel um modelo de raios para localizar uma fonte estatica com acuracia comparavel aquela tradicionalmente obtida por um modelo de modos normais. Palavras-chave: modelagem acustica submarina, modelos de raios, modelos de modos normais.