title: Effects of coating on the optical trapping efficiency of microspheres via geometrical optics approximation.
abstract: We present the optical trapping forces that are generated when a single laser beam strongly focuses on a coated dielectric microsphere. On the basis of geometrical optics approximation (GOA), in which a particle intercepts all of the rays that make up a single laser beam, we calculate the trapping forces with varying coating thickness and refractive index values. To increase the optical trapping efficiency, the refractive index (n(b)) of the coating is selected such that n(a) < n(b) < n(c), where na and nc are the refractive indices of the medium and the core material, respectively. The thickness of the coating also increases trapping efficiency. Importantly, we find that trapping forces for the coated particles are predominantly determined by two rays: the incident ray and the first refracted ray to the medium.
authors.affiliation: Department of Chemical Engineering, Kyung Hee University , Yongin-si, Gyeonggi-do 446-701, South Korea.
authors.forename: Bum Jun
authors.initials: BJ
authors.lastname: Park
authors.forename: Eric M
authors.initials: EM
authors.lastname: Furst
mesh_terms: D008863:Microspheres; D055620:Optical Phenomena