Light scattering by multi-layered ellipsoidal particles
                   in quasi-static approximation

                           V.G.Farafonov
         St.Petersburg University of Aerocosmic Instrumentation
                   St.Petersburg, 190000, Russia

                                and

                             V.B.Il'in
           Astronomical Institute, St.Petersburg University
                  St.Petersburg, 198504, Russia


                             ABSTRACT

Calculation of light scattering by finite size non-axisymmetric inhomogeneous
particles is a complicated problem whose solution by the exact methods (e.g.,
the Discrete Dipole Approximation) is very computational time consuming.
Therefore any approximate solution of the problem for multi-layered
ellipsoidal particles is of interest.

A recent review on approximate approaches presented in [1] describes the
current state of the Rayleigh, Rayleigh-Gans, anomalous diffraction and
other approximations for homogeneous and core/mantle particles.
The Rayleigh approximation for multi-layered confocal and non-confocal
ellipsoids was developed in [2,3] only after the appearance of the book [1].

A not sufficient space in the review was devoted to the quasi-static
approximation being a generalization of the Rayleigh and Rayleigh-Gans
approximations, when the field inside a homogeneous particle is represented
by the incident field similarly to the Rayleigh-Gans approximation,
taking into account the particle polarizability like in the Rayleigh
approximation (see [4-7] for more details). For multi-layered particles,
the polarizability is calculated in a special way using the Rayleigh
approximation [6].

It should be emphasized that the quasi-static approximation has an
essentially wider range of applicability than the Rayleigh and Rayleigh-Gans
approximations [5-6]. The  approximation works in particular efficiently
in the case of strongly elongated or flattened particles [6-7]. For
homogeneous spheroids, the quasi-static approximation was shown to give
the main term of the asymptotics of scattered radiation in the limit of
small values of the aspect ration of the particles [7] (see also [8-9]
for more details).

In this paper we consider light scattering by multi-layered (non-confocal)
ellipsoidal and spheroidal particles in the quasi-static approximation.
Some results obtained for ensembles of such particles are presented as well.

The work was partly supported by INTAS (grant 99/652).


                          References:

 1. Mishchenko M.I., Hovenier J.W., Travis L.D. (2000) Light Scattering by
    Non-Spherical Particles, Acad. Press.
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 3. Farafonov V.G. (2000) Opt. Spectr. in press.
 4. Farafonov V.G. (1994) Opt. Spectr. 77, 402.
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