Extension of geometrical-optics approximation to on-axis Gaussian beam scattering. II. By a spheroidal particle with end-on incidence
ABSTRACT On the basis of our previous work on the extension of the geometrical-optics approximation to Gaussian beam scattering by a spherical particle, we present a further extension of the method to the scattering of a transparent or absorbing spheroidal particle with the same symmetric axis as the incident beam. As was done for the spherical particle, the phase shifts of the emerging rays due to focal lines, optical path, and total reflection are carefully considered. The angular position of the geometric rainbow of primary order is theoretically predicted. Compared with our results, the Möbius prediction of the rainbow angle has a discrepancy of less than 0.5 degrees for a spheroidal droplet of aspect radio kappa within 0.95 and 1.05 and less than 2 degrees for kappa within 0.89 and 1.11. The flux ratio index F, which qualitatively indicates the effect of a surface wave, is also studied and found to be dependent on the size, refractive index, and surface curvature of the particle.
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ABSTRACT: We have developed a novel model – Vectorial Complex Ray Model (VCRM) – for the scattering of a smooth surface objet of arbitrary shape. In this model, a wave is described by bundles of rays, and a ray is characterized not only by its direction and amplitude but also the curvature and the phase of the wave. These new properties allow to take into account the phase shift due to the focal lines of an arbitrary shaped wave and the amplitude due to the divergence/convergence of the wave. The interferences can therefore be calculated correctly for an arbitrarily shaped particle of smooth surface. In this paper, we present an application of the VCRM in the 2D scattering of a plane wave by a homogeneous ellipsoid at oblique incidence. The transversal divergence effect of the wave will be discussed. The rainbows of ellipsoidal droplet and bubble are investigated.Journal of Quantitative Spectroscopy and Radiative Transfer 12/2012; 113(18):2419–2423. DOI:10.1016/j.jqsrt.2012.04.015 · 2.29 Impact Factor
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ABSTRACT: The geometrical-optics approximation of light scattering by a transparent or absorbing spherical particle is extended from plane wave to Gaussian beam incidence. The formulas for the calculation of the phase of each ray and the divergence factor are revised, and the interference of all the emerging rays is taken into account. The extended geometrical-optics approximation (EGOA) permits one to calculate the scattering diagram in all directions from 0 degrees to 180 degrees. The intensities of the scattered field calculated by the EGOA are compared with those calculated by the generalized Lorenz-Mie theory, and good agreement is found. The surface wave effect in Gaussian beam scattering is also qualitatively analyzed by introducing a flux ratio factor. The approach proposed is particularly important to the further extension of the geometrical-optics approximation to the scattering of large spheroidal particles.Applied Optics 08/2006; 45(20):4990-9. DOI:10.1364/AO.45.004990 · 1.78 Impact Factor
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ABSTRACT: The principle of the critical angle refractometry and sizing technique is extended to characterize the size distribution and the mean refractive index of clouds of bubbles. For a log-normal bubble-size distribution, simulations show that the mean size, the relative width of the size distribution, and the mean refractive index of the bubbles have a particular and easily identified influence on the critical scattering patterns. Preliminary experimental results on air bubble/water flows clearly demonstrate the potential and robustness of this new technique for bubbly flow characterization.Optics Letters 08/2007; 32(14):2070-2. DOI:10.1364/OL.32.002070 · 3.18 Impact Factor