Light scattering by a core-mantle spheroidal particle.

A solution of the electromagnetic scattering problem for confocal coated spheroids has been obtained by the method of separation of variables in a spheroidal coordinate system. The main features of the solution are (i) the incident, scattered, and internal radiation fields are divided into two parts: an axisymmetric part independent of the azimuthal angle ? and a nonaxisymmetric part that with integration over ? gives zero; the diffraction problems for each part are solved separately; (ii) the scalar potentials of the solution are chosen in a special way: Abraham's potentials (for the axisymmetric part) and a superposition of the potentials used for spheres and infinitely long cylinders (for the nonaxisymmetric part). Such a procedure has been applied to homogeneous spheroids [Differential Equations 19, 1765 (1983); Astrophys. Space Sci. 204, 19, (1993)] and allows us to solve the light scattering problem for confocal spheroids with an arbitrary refractive index, size, and shape of the core or mantle. Numerical tests are described in detail. The efficiency factors have been calculated for prolate and oblate spheroids with refractive indices of 1.5 + 0.0 i, 1.5 + 0.05 i for the core and refractive indices of 1.3 + 0.0 i, 1.3 + 0.05i for the mantle. The effects of the core size and particle shape as well as those of absorption in the core or mantle are examined. It is found that the efficiency factors of the coated and homogeneous spheroids with the volume-averaged refractive index are similar to first maximum.