Light Scattering by Regular Particles on Flat Substrates

Abstract

Light scattering intensity patterns produced by particles on substrates depend strongly on the size and shape of the particles. For some regular particle shapes, like spheres and cylinders, minima exist in the intensities and a relationship exists between their angular positions and the particle size. This dependence may be established using a simple double-interaction model which considers only the following: a) the scattering solution for the isolated particle; b) the coherent addition of four contributions of the scattering amplitudes to account for the field reflections off the substrate; and c) some geometrical factors which include the path differences, the Fresnel reflection coefficients, and the geometrical shadowing. This model has been used to size particles when illuminated at both normal and oblique incidence. For a collection of polydisperse particles on a substrate, scattering patterns can also produce very useful information; for instance, the visibility of the minima is directly related to the variance in size for low polydispersity samples. For large values of polydispersity (more than 30%), the width of the enhanced-backscattering peak can provide useful information.