Study of the refractive index of microscopic glass beads by light-refraction analysis

The refractive index of submillimeter glass beads has been measured by means of a novel, to our knowledge, procedure with reference liquids that does not require close index matching and therefore avoids the use of toxic compounds for high-index glasses (i.e., n >/= 1.8). The method is based on the analysis of the light refracted by a monolayer of beads in comparison with ray-tracing simulations. For the three different types of glass beads investigated a satisfactory fit is achieved by the assumption of a radial variation of the refractive index inside the beads. This is ascribed to the tensile and compressive stresses originating inside the beads during rapid solidification of the glass.