Jiajie Wang

Study of scattering from a sphere with an eccentrically located spherical inclusion by generalized Lorenz-Mie theory: internal and external field distribution.

Based on the recent results in the generalized Lorenz-Mie theory, solutions for scattering problems of a sphere with an eccentrically located spherical inclusion illuminated by an arbitrary shaped electromagnetic beam in an arbitrary orientation are obtained. Particular attention is paid to the description and application of an arbitrary shaped beam in an arbitrary orientation to the scattering problem under study. The theoretical formalism is implemented in a homemade computer program written in FORTRAN. Numerical results concerning spatial distributions of both internal and external fields are displayed in different formats in order to properly display exemplifying results. More specifically, as an example, we consider the case of a focused fundamental Gaussian beam (TEM(00) mode) illuminating a glass sphere (having a real refractive index equal to 1.50) with an eccentrically located spherical water inclusion (having a real refractive index equal to 1.33). Displayed results are for various parameters of the incident electromagnetic beam (incident orientation, beam waist radius, location of the beam waist center) and of the scatterer system (location of the inclusion inside the host sphere and relative diameter of the inclusion to the host sphere).

Morphology-dependent resonances in an eccentrically layered sphere illuminated by a tightly focused off-axis Gaussian beam: parallel and perpendicular beam incidence

Following the recent results in generalized Lorenz–Mie theory concerning the description of an arbitrary shaped electromagnetic beam propagating in an arbitrary orientation, a theoretical investigation of morphology-dependent resonances (MDRs) excited in a sphere with an eccentrically located spherical inclusion illuminated by a tightly focused Gaussian beam is presented. Calculations of extinction efficiency spectra and backward-scattering intensity spectra are made for different locations and radii of the inclusion with respect to the host sphere. Exemplifying field distributions inside of the scatterer under both off-resonance and on-resonance conditions are exhibited. The influences of the relative size of the inclusion with respect to the host sphere and of the separation distance between the two sphere centers on the positions and on the amplitudes of the MDRs peaks are studied. As are the cases for spheres and concentrically multilayered spheres, the resonance positions of MDRs in an eccentrically layered sphere are located at the same size parameter for Gaussian beam illumination and for plane-wave illumination. In contrast with the lift of azimuthal modes m degeneracy in MDR peaks for an eccentric sphere illuminated obliquely by a plane wave, we display a kind of lift that cannot be observed in extinction efficiency spectra with an oblique illumination of a tightly focused Gaussian beam. Nevertheless, asymmetric distributions of the internal field inside of the eccentric sphere at resonance conditions are observed both with an oblique illumination of a tightly focused beam and with an oblique illumination of a plane-wave illumination. Interpretation from a perspective of the localization principle is applied to the simulation results.

Photonic jet generated by spheroidal particle with Gaussian-beam illumination

Within the framework of generalized Lorenz–Mie theory, the properties of three-dimensional photonic jets emerging from spheroidal particles illuminated by a focused Gaussian beam are studied. The intensity, focal distance, and transverse and longitudinal dimensions of a photonic jet depending on the ellipticity of the spheroidal particle are numerically investigated. The simulation results show that, by simply varying the ellipticity, it is possible to obtain localized photon fluxes having different power characteristics and spatial dimensions. This can be of interest for several applications, such as high-resolution (nanometer scale) optical sensors, subdiffraction-resolution optical virtual imaging, and ultradirectional optical antennas.

Internal and near-surface electromagnetic fields for a dielectric spheroid illuminated by a zero-order Bessel beam

Within the framework of generalized Lorenz-Mie theory, scattering from a homogeneous spheroidal particle illuminated by an on-axis zero-order Bessel beam is formulated analytically, with special attention paid to the investigation of internal and near-surface fields. Numerical results concerning the spatial distributions of internal and near-surface fields are presented for various parameter values, such as the half-cone angle of the incident zero-order Bessel beam, the major axis, the minor axis, and the refractive index of the spheroid. The study of internal and near-surface field distributions will contribute to the understanding of Bessel beam scattering by nonspherical particles with sizes close to the incident wavelength.

Note on the use of localized beam models for light scattering theories in spherical coordinates

Localized beam models provide the most efficient and enlightening ways to evaluate beam shape coefficients of electromagnetic arbitrary shaped beams for use in light scattering theories. At the present time, they are valid in spherical and (circular and elliptical) cylindrical coordinates. A misuse of localized beam models in spherical coordinates recently appeared several times in the literature. We therefore present a warning to avoid the propagation of an incorrect use of localized beam models.

On the validity of the integral localized approximation for Bessel beams and associated radiation pressure forces

In this paper we investigate the integral version of the localized approximation (ILA)-a powerful technique for evaluating the beam shape coefficients in the framework of the generalized Lorenz-Mie theory-as applied to ideal scalar Bessel beams (BBs). Originally conceived for arbitrary shaped beams with a propagating factor exp(±ikz), it has recently been shown that care must be taken when applying the ILA for the case of ideal scalar BBs, since they carry a propagating factor exp(±ikz cos α), with α being the axicon angle, which cannot be smoothly accommodated into its mathematical formalism. Comparisons are established between the beam shape coefficients calculated from both ILA and exact approaches, assuming paraxial approximation and both on- and off-axis beams. Particular simulations of radiation pressure forces are provided based on the existing data in the literature. This work helps us in elucidating that ILA provides adequate beam shape coefficients and descriptions of ideal scalar BBs up to certain limits and, even when it fails to do so, reliable information on the physical optical properties of interest can still be inferred, depending on specific geometric and electromagnetic aspects of the scatterer.

Controllable and enhanced photonic jet generated by fiber combined with spheroid

Dielectric microparticles are used as simple and low-cost means to achieve strong intensity confinement below the standard diffraction limit. Here we report the demonstration of enhanced light intensity in the vicinity of optical fiber combined with dielectric spheroidal particles. Specific attention is paid to the study of the influences of the spheroids ellipticity (ratio of horizontal length to vertical length) as well as the refractive index on the intensity enhancement and focal distance. It reveals that simply varying the ellipticity, it is possible to obtain localized photon fluxes having different characteristics. This could yield a new superenhanced intensity device with excellent optical properties and low manufacturing cost for using visible light in many areas of biology, material sciences, chemistry, medicine, and tissue engineering.

Implementation of nondiffracting Bessel beam sources in FDTD for scattering by complex particles

In this paper, the nondiffracting Bessel beam sources are implemented in finite-difference time-domain (FDTD) method. The high-order scattered-field algorithm of the FDTD (SF-FDTD (2, 4)) method is employed to investigate the scattering of particles illuminated by Bessel beams. In the SF-FDTD (2, 4) method, the scattered fields of the whole region are calculated directly by time stepping and the incident fields are obtained by the vector expressions of the diffraction-free Bessel beam. Some numerical results are included to illustrate the validity and capability of the proposed method. This study is expected to provide a new efficient method to investigate the interactions between nondiffracting beams and complex particles.

Electromagnetic scattering of an aggregate of particles illuminated by an arbitrary shaped beam

In this paper, an analysis of scattering properties of aggregated particles illuminated by an arbitrary shaped beam is implemented using GLMT. A theoretical treatment for an aggregate of particles illuminated by an arbitrarily incident beam is briefly presented, with special attention paid to the calculation of beam shape coefficients of a shaped beam. The theoretical treatment and the home-made codes are verified by making a comparison between our numerical results and those obtained using a public available T-Matrix code MSTM. Good agreements are achieved which partially indicate the correctness of both codes. Furthermore, some new numerical results concerning the scattered fields of aggregated particles illuminated by a focused Gaussian beam are presented.

Analysis of electromagnetic scattering characteristics of plasma sheath surrounding a hypersonic aerocraft based on high-order auxiliary differential equation finite-difference time-domain

A numerical analysis of electromagnetic (EM) scattering characteristics of a hypersonic aerocraft enveloped by a plasma sheath is presented. The flow field parameters around a hypersonic aerocraft ...