Light scattering signatures of individual spheres on optically smooth conducting surfaces

The differential (angle-resolved) light scattering characteristics of spheres deposited on an optically smooth polished nickel surface were studied. In the experimental work a He-Ne laser beam (632.8 nm) illuminated individual polystyrene spheres of diameters 0.50, 1.09, 2.02, and 4.10 microm. The laser beam was directed onto the surface at 45 degrees angle of incidence and focused to 15-microm l/e(2) diameter. A ring/wedge photodiode detector array centered about the specularly reflected beam collected the light scattered into twenty one ring-shaped elements ranging from ~17 degrees to 62 degrees from the specular direction. For comparison with experiment a theoretical model which partially uncoupled the scattering by the surface and the particle was developed based on extensions of Lorenz-Mie theory. The scattering measurements showed reasonable agreement with the model and indicated that the formulation can be adapted for first-order predictions of light scattering by spherical particles on optically smooth surfaces.