An extension to the Rayleigh–Gans formula: model of partially absorbing particles

The Rayleigh–Gans (R–G) approximation is widely employed in various optical models to simulate the optical response of transparent media. However, the R–G concept can only succeed if the refractive index of scatterers approaches that of surrounding medium. In addition, the sizes of scattering domains are assumed to be small enough. Because of these reasons, the validity of R–G solution is fairly limited. In this paper, a semi-analytical extension to the R–G theory is introduced, resulting in an approximate formula for efficiency factor for scattering Qsca. It is proven numerically that this formula works much better than that for traditional R–G model. The computations have been made on absorbing particles with sizes comparable to or smaller than the wavelength of an incident radiation. The conventional R–G theory is either inapplicable or at least inappropriate for such particles.