Kuan Fang Ren

Improved algorithm for electromagnetic scattering of plane waves and shaped beams by multilayered spheres

An efficient numerical procedure for computing the scattering coefficients of a multilayered sphere is discussed. The stability of the numerical scheme allows us to extend the feasible range of computations, both in size parameter and in number of layers for a given size, by several orders of magnitude with respect to previously published algorithms. Exemplifying results, such as scattering diagrams and cross-sectional curves, including the case of Gaussian beam illumination, are provided. Particular attention is paid to scattering at the rainbow angle for which approaches based on geometrical optics might fail to provide accurate enough results.

Radiation pressure forces exerted on a particle arbitrarily located in a Gaussian beam by using the generalized Lorenz-Mie theory, and associated resonance effects

Abstract Radiation pressure force components on a particle arbitrarily located in a Gaussian beam are computed within the framework of the generalized Lorenz-Mie theory. Beside reference data, results relevant to optical levitation experiments are provided and the influence of the Gaussian character of the beam on resonance structures is discussed.

Prediction of reverse radiation pressure by generalized Lorenz-Mie theory.

Radiation pressure exerted on a spherical particle by one extremely focused Gaussian beam is investigated by the use of generalized Lorenz-Mie theory (GLMT). Particular attention is devoted to reverse radiation pressure. GLMT predictions for different descriptions of the incident beam are compared with electrostriction predictions when the particle size is smaller than the wavelength and with geometric-optics predictions when the particle size is larger than the wavelength.

Integral localized approximation in generalized Lorenz–Mie theory

The generalized Lorenz-Mie theory deals with the interaction between spheres and arbitrarily shaped illuminating beams. An efficient use of the theory requires efficient evaluation of the so-called beam-shape coefficients involved in the description of the illuminating beam. A less time-consuming method of evaluation relies on the localized approximation. However, it lacks flexibility when the description of the illuminating beam is modified. We present a new version of this method, called the integral localized approximation, that exhibits the desired property of flexibility.

SCATTERING OF A GAUSSIAN BEAM BY AN INFINITE CYLINDER IN THE FRAMEWORK OF GENERALIZED LORENZ-MIE THEORY : FORMULATION AND NUMERICAL RESULTS

We study the scattering of Gaussian beams by infinite cylinders in the framework of the so-called generalized Lorenz–Mie theory for cylinders. The general theory is expressed by using the theory of distributions. Several descriptions of the illuminating Gaussian beams are considered—i.e., Maxwellian beams at limited order, quasi-Gaussian beams defined by a plane-wave spectrum, and the cylindrical localized approximation—leading to different specific formulations. In the last two cases, the theory in terms of distributions reduces to theories expressed in terms of usual functions.

Discussion of two quadrature methods of evaluating beam-shape coefficients in generalized Lorenz–Mie theory

A comparison between two quadrature methods of evaluating beam-shape coefficients in generalized Lorenz-Mie theory, in the case of incident Gaussian beams, is carried out. It is shown that, when the electromagnetic description of the Gaussian beams does not perfectly satisfy Maxwells equations, both quadrature methods are basically flawed. These flaws do not prevent an accurate evaluation of beam-shape coefficients when their nature is correctly identified, because they produce artifacts that can easily be identified and removed.

Generalized Lorenz-Mie theory for an arbitrarily oriented, located, and shaped beam scattered by a homogeneous spheroid

The theory of an arbitrarily oriented, shaped, and located beam scattered by a homogeneous spheroid is developed within the framework of the generalized Lorenz-Mie theory (GLMT). The incident beam is expanded in terms of the spheroidal vector wave functions and described by a set of beam shape coefficients (G(m)(n),(TM),G(m)(n),(TE)). Analytical expressions of the far-field scattering and extinction cross sections are derived. As two special cases, plane wave scattering by a spheroid and shaped beam scattered by a sphere can be recovered from the present theory, which is verified both theoretically and numerically. Calculations of the far-field scattering and cross sections are performed to study the shaped beam scattered by a spheroid, which can be prolate or oblate, transparent or absorbing.

Scattering of a Gaussian beam by an infinite cylinder with arbitrary location and arbitrary orientation: numerical results

We present numerical results concerning the properties of the electromagnetic field scattered by an infinite circular cylinder illuminated by a circular Gaussian beam. The cylinder is arbitrarily located and arbitrarily oriented with respect to the illuminating Gaussian beam. Numerical evaluations are provided within the framework of a rigorous electromagnetic theory, the generalized Lorenz-Mie theory, for infinite cylinders. This theory provides new insights that could not be obtained from older formulations, i.e., geometrical optics and plane-wave scattering. In particular, some emphasis is laid on the waveguiding effect and on the rainbow phenomenon whose fine structure is hardly predictable by use of geometrical optics.

Debye series for light scattering by a multilayered sphere

We have derived the formula for the Debye-series decomposition for light scattering by a multilayered sphere. This formulism permits the mechanism of light scattering to be studied. An efficient algorithm is introduced that permits stable calculation for a large sphere with many layers. The formation of triple first-order rainbows by a three-layered sphere and single-order rainbows and the interference of different-order rainbows by a sphere with a gradient refractive index, are then studied by use of the Debye model and Mie calculation. The possibility of taking only one single mode or several modes for each layer is shown to be useful in the study of the scattering characteristics of a multilayered sphere and in the measurement of the sizes and refractive indices of particles.

Evaluation of laser-sheet beam shape coefficients in generalized Lorenz–Mie theory by use of a localized approximation

The use of laser sheets is of growing interest in many measurement techniques relying on light scattering. Device performances must often be analyzed with generalized Lorenz–Mie theory, which requires the evaluation of beam shape coefficients describing the incident beams. In the case of Gaussian beams these coefficients are most efficiently computed by a localized approximation. The localized approximation procedure for Gaussian beams is here successfully generalized to the case of laser sheets.