GEOMETRICAL-OPTICS AND DIFFRACTION VIS-A-VIS MIE THEORY OF SCATTERING OF ELECTROMAGNETIC-RADIATION BY A SPHERE

The usefulness of the classical Geometrical Optics and Diffraction (GOD) has been illustrated for scattering of electromagnetic radiation by very large dielectric and absorbing spheres. Various scattering parameters such as extinction efficiency, asymmetry parameter, radiation pressure, etc., have been calculated on the basis of GOD and compared with the equivalent results obtained as per the Mie theory. The spheres are assumed to be composed of pure and impure silicate-like or polystyrene material in the visual wavelengths. The representative indices of refraction m = m' - im" are chosen to be m' = 1.6 and m" = 0.00, 0.05, 0.10, 0.30, 1.00, 2.00, and 4.00. It is shown that the asymptotic values of a given scattering parameter obtained from the Mie theory calculations agree reasonably well with the corresponding result based on GOD. It is thus possible to estimate the minimum value (x(min)) of the size-to-wavelength parameter x ( = 2-pi-a/lambda; a, the radius of the sphere; and lambda, the wavelength of the incident radiation), such that, for x > x(min), GOD holds good for certain specified accuracy.