Calculation of the optical properties of core-mantle spheroids with non-confocal boundaries of the mantle

An exact solution to the problem of light scattering by a spheroidal particle with non-confocal layer boundaries is obtained. The algorithm of the solution presented includes the main achievements of the theory of last years. Using the procedures for calculating spheroidal functions recently created by van Buren, a program has been developed that implements the proposed algorithm in the case of two-layer spheroids. The convergence and accuracy of the solution is investigated for spheroidal particles of 4 types: with the confocal core and envelope, with similar shapes of them, with the most spherical and the most elongated/flattened shape of the core when the core to envelope volume ration is constant. Cross sections of two-layer spheroids of these types calculated at high values of the diffraction parameter (up to $x_a = 2\pi a/\lambda$ = 120) are considered and compared with the predictions of the approximate theory of anomalous diffraction. The results of computations of the scattering matrix elements are also presented. They demonstrate that usually considered confocal layer spheroids well describe only the optical properties of particles with similar core and shell shapes.