On light scattering by two-layer ellipsoids with nonconfocal boundaries

We consider new approaches to the calculation of the optical properties of small nonspherical layered particles whose layer boundaries are nonconfocal concentric coaxial ellipsoids. A simple analytical approximation is proposed and substantiated for the case in which the size of these particles is much smaller than the wavelength of the incident radiation. The approximation is found to yield results with an error of 3 $\times$ 10$^{-3}$ for the diffraction parameter $x<$ 0.1. An approach to the calculation of the optical properties of nonconfocal ellipsoids is justified, which consists of the replacement of nonconfocal boundaries with confocal ones, with the layer volumes being preserved. We show that the error of this approach for dielectric particles is a few percent at $x<$ 1 and about 20% at $x<$ 5. It is noted that both approximations can be easily extended to the case of multilayer nonconfocal ellipsoids.