B. Maheu

Light scattering from a sphere arbitrarily located in a Gaussian beam, using a Bromwich formulation

We present a theoretical description of the scattering of a Gaussian beam by a spherical, homogeneous, and isotropic particle. This theory handles particles with arbitrary size and nature having any location relative to the Gaussian beam. The formulation is based on the Bromwich method and closely follows Kerker’s formulation for plane-wave scattering. It provides expressions for the scattered intensities, the phase angle, the cross sections, and the radiation pressure.

Localized interpretation to compute all the coefficients gnm in the generalized Lorenz–Mie theory

Numerical computations in the framework of the generalized Lorenz–Mie theory require the evaluation of a new double set of coefficients gn,TMm and gn,TEm (n = 1, …, ∞; m = − n, … +n). A localized interpretation of these coefficients is designed to permit fast and accurate computations, even on microcomputers. When the scatter center is located on the axis of the beam, a previously published localized approximation for a simpler set of coefficients gn is recovered as a special case. The subscript n in coefficients gn and gnm is associated with ray localization and discretization of space in directions perpendicular to the beam axis, while superscript m in coefficients gnm is associated with azimuthal wave modes.

Scattering of laser beams by Mie scatter centers: numerical results using a localized approximation

Relying on van de Hulst’s localization principle, a localized approximation to the generalized Lorenz-Mie theory is introduced. The validation of this simple approximation is obtained from numerical comparisons the Rayleigh-Gans theory. Other comparisons concerning scattering profiles are carried out first with theoretical data published in the literature and later with experimental measurements. Original results are given for coal particles as an example of the versatility of the method.

Computations of the gn coefficients in the generalized Lorenz-Mie theory using three different methods

Three different methods can be used to numerically compute the g(n) coefficients in the generalized Lorenz-Mie theory. Two of them are rigorous and involve (i) numerical evaluation of quadratures and (ii) numerical evaluation of finite series. The third way relies on the so-called localized interpretation that we discussed in previous papers. These three methods are discussed and compared.

Ray localization in gaussian beams

Abstract In the framework of a theory for gaussian beam scattering by spherical objects, a localized interpretation can be used for easier computation of the main coefficients. This localized interpretation, together with our numerical results, shows a kind of ray localization, the beam being then interpreted as a bundle of cylindrical ray shells.

Scattering of a Gaussian Beam by a Sphere Using a Bromwich Formulation : Case of an Arbitrary Location

The present paper is devoted to the generalization1 of the Mie scattering theory for a sphere illuminated by a plane wave to the case when the scatter center is illuminated by a Gaussian beam. Such a fundamental theory may lead, in other steps, to important applications in optical sizing, by enabling the researchers to design rigorous approaches to the principles of a few optical sizing methods (the visibility or the phase Doppler techniques, for instance).

EVALUATIONS OF THE SIGHTING DISTANCE IN A FOGGY ATMOSPHERE BY MONTE CARLO SIMULATION

Abstract A code for the simulation of light propagation in multiple scattering media is presented. Unlike the analytical methods which generally require simplifying assumptions, the MUSCAT (MUltiple SCATtering) code only needs general assumptions, namely steady-state and scalar radiative transfer. Knowing the 3D-geometrical and photometrical characteristics of sources and detectors and the albedo, extinction coefficient and phase function of the scattering medium, the code computes what will be detected. A concrete application is presented: the sighting distance of a foglight in a foggy night atmosphere is evaluated for a real driving situation. The road is perfectly absorbent and two cases are compared: the road is lit either by a headlight or by one-sided street lamps. The sighting distance of a 60% reflexive target is also computed and the same comparison is done.

Average crossing parameter and forward scattering ratio values in four-flux model for multiple scattering media

Abstract The four-flux model for multiple scattering media allows one to evaluate scattering properties (reflectances, transmittances) by using simple formulae which may even be readily handled by pocket calculators. Unfortunately, it involves parameters ϵ , called the average crossing parameter, and ζ , called forward scattering ratio, which cannot be a priori evaluated in the framework of the four-flux model, excepted in special cases (collimated radiation or semi-isotropic diffuse radiation). It however happens that the four-flux model can be extended to larger fields of applications if the average crossing parameter and the forward scattering ratio, originally defined as physical quantities, are viewed adjustable parameters. This paper is devoted to the evaluation of these free parameters, allowing one to carry out more accurate four-flux computations.