Radiation forces on a micrometer-sized sphere in an evanescent field

Electromagnetic wave theory is used to predict the radiation forces exerted upon a micrometer-sized spherical particle illuminated by evanescent waves penetrating across a dielectric interface. These forces are quantified for two incident beam polarizations (p and s polarization) and for different refractive-index media. The electromagnetic formalism that we use is based on theoretical studies of Barton et al. [J. Appl. Phys. 64, 1632 (1988); 66, 4594 (1989)]. The novelty of the present research is to apply this general formalism to the calculation of forces when the evanescent field is identified with the incident field. Our theoretical results for the horizontal and vertical force components are shown graphically in nondimensional form as functions of the size parameter of the sphere. Moreover, our results are found to be in reasonable agreement with recent experimental findings of Kawata and Sugiura [Opt. Lett. 17, 772 (1992)]. (C) 1995 Optical Society of America