title: Focused plasmonic trapping of metallic particles.
abstract: Scattering forces in focused light beams push away metallic particles. Thus, trapping metallic particles with conventional optical tweezers, especially those of Mie particle size, is difficult. Here we investigate a mechanism by which metallic particles are attracted and trapped by plasmonic tweezers when surface plasmons are excited and focused by a radially polarized beam in a high-numerical-aperture microscopic configuration. This contrasts the repulsion exerted in optical tweezers with the same configuration. We believe that different types of forces exerted on particles are responsible for this contrary trapping behaviour. Further, trapping with plasmonic tweezers is found not to be due to a gradient force balancing an opposing scattering force but results from the sum of both gradient and scattering forces acting in the same direction established by the strong coupling between the metallic particle and the highly focused plasmonic field. Theoretical analysis and simulations yield good agreement with experimental results.
authors.affiliation: 1] Institute of Modern Optics, Key Laboratory of Optical Information Science and Technology, Ministry of Education of China, Nankai University, Tianjin 300071, China [2].
authors.forename: Changjun
authors.initials: C
authors.lastname: Min
authors.forename: Zhe
authors.initials: Z
authors.lastname: Shen
authors.forename: Junfeng
authors.initials: J
authors.lastname: Shen
authors.forename: Yuquan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Hui
authors.initials: H
authors.lastname: Fang
authors.forename: Guanghui
authors.initials: G
authors.lastname: Yuan
authors.forename: Luping
authors.initials: L
authors.lastname: Du
authors.forename: Siwei
authors.initials: S
authors.lastname: Zhu
authors.forename: Ting
authors.initials: T
authors.lastname: Lei
authors.forename: Xiaocong
authors.initials: X
authors.lastname: Yuan