REFRACTION BY SPHERICAL-PARTICLES IN THE INTERMEDIATE SCATTERING REGION

Mie theory computations of the refraction efficiency for spherical par ticles are compared with predictions of the Rayleigh, Rayleigh-Gans an d Anomalous Diffraction approximations. Attention is given to the inte rmediate region of particle size, where for extinction the Rayleigh-Ga ns and Anomalous Diffraction approximations have been shown to merge w ith each other and with Mie computations. In this region the Mie refra ction efficiency is shown to have a first maximum which is not given b y any approximation. The Rayleigh and Rayleigh-Gans refraction efficie ncies are independent of particle size and approximate to the Mie resu lts in the intermediate region, but not at larger particle sizes. Apar t from the first maximum, the AD approximation is shown to closely pre dict the extrema and zeros of the refraction efficiency. In the interm ediate region the Mie computations reveal a first maximum in the refra ction efficiency which is not modelled by either of the RG or the AD a pproximations. Consequently a region where the Rayleigh-Gans and Anoma lous Diffraction approximations merge with each other and with Mie com putations is not found for refraction. The first maximum in refraction efficiency predicted by the Mie theory occurs when the optical wavele ngth inside a particle is about 20% greater than the particle's diamet er. It is shown to result mainly from the contributions to refraction by the magnetic dipole and electric quadrupole.