Scattering of Light by Spherical Liquid Droplets Using Computer-Synthesized Holograms

Abstract

A cathode-ray tube linked to a computer is used to synthesize holograms of spherical liquid droplets illuminated by plane waves of monochromatic linearly polarized light. The classical Mie solution is employed to determine the far-field radiation pattern of the light waves scattered by the droplets. The most distinctive maxima and minima in the radiation pattern of a droplet are found to occur in the side scattering adjacent to the forward lobe, when the droplet is viewed in a plane that is perpendicular to the direction of polarization of the incident waves. Typical examples of these maxima and minima were recorded on the computed holograms. The reference source was an electric dipole with its axis of polarization parallel to the direction of polarization of the light waves incident on the droplets. Reconstructed droplet images were obtained from the computed holograms using a low-power He–Ne laser source. The reconstructed images were found to show all of the appropriate maxima and minima in the radiation pattern. A holographic method is suggested in the paper for determining the size of spherical liquid droplets in the range of diameters from about 0.5 to 20 μ. This method is based on the techniques used in the construction of the computed holograms and depends on the relation between the angles of the maxima and minima and size parameter ka.