Spheroidal core-mantle particle absorption, scattering, and polarisation in the long-wavelength limit

TL;DR

This paper introduces an analytical method for calculating the optical properties of spheroidal core-mantle particles in the long-wavelength limit, offering a faster alternative to numerical methods with good accuracy.

Contribution

The authors develop and validate an analytical approach for spheroidal core-mantle particle optical properties, applicable at long wavelengths, improving efficiency over numerical techniques.

Findings

Analytical method agrees well with DDSCAT numerical calculations.

Method is faster and simpler than numerical approaches.

Cautions against using EMT for core/mantle particles.

Abstract

The numerical calculation of optical properties (extinction, absorption, scattering and polarisation efficiencies) is often time-consuming for non-spherical and inhomogeneous particles. Where possible analytical methods are therefore to be preferred. We provide an analytical tool to derive the optical properties of mantled spheroidal particles, of arbitrary axis ratio, in the long wavelength limit (a << lambda), where the mantle form may be confocal, co-axial or of constant depth with respect to the particle core. We have developed an analytical approach to spheroidal core/mantle particle optical property calculations. The analytical method compares well with DDSCAT numerical calculations and, under limited circumstances, with those made using the Bruggemann effective medium theory (EMT).The analytical method presented here provides a useful tool to explore the optical and polarisation properties of core/mantle spheroidal particles at long wavelengths (lambda >~ 8mu) and is simpler and faster to implement than corresponding numerical methods. We caution against the use of EMT methods in approximating the optical properties of core/mantle particles.