title: Nonlinear force dependence on optically bound micro-particle arrays in the evanescent fields of fundamental and higher order microfibre modes.
abstract: Particles trapped in the evanescent field of an ultrathin optical fibre interact over very long distances via multiple scattering of the fibre-guided fields. In ultrathin fibres that support higher order modes, these interactions are stronger and exhibit qualitatively new behaviour due to the coupling of different fibre modes, which have different propagation wave-vectors, by the particles. Here, we study one dimensional longitudinal optical binding interactions of chains of 3 μm polystyrene spheres under the influence of the evanescent fields of a two-mode microfibre. The observation of long-range interactions, self-ordering and speed variation of particle chains reveals strong optical binding effects between the particles that can be modelled well by a tritter scattering-matrix approach. The optical forces, optical binding interactions and the velocity of bounded particle chains are calculated using this method. Results show good agreement with finite element numerical simulations. Experimental data and theoretical analysis show that higher order modes in a microfibre offer a promising method to not only obtain stable, multiple particle trapping or faster particle propulsion speeds, but that they also allow for better control over each individual trapped object in particle ensembles near the microfibre surface.
authors.affiliation: Light-Matter Interactions Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan.|Physics Department, University College Cork, Cork, Ireland.
authors.forename: Aili
authors.initials: A
authors.lastname: Maimaiti
authors.affiliation: Institute for Theoretical Physics, University of Innsbruck, Technikerstrasse 25, A-6020, Innsbruck, Austria.
authors.forename: Daniela
authors.initials: D
authors.lastname: Holzmann
authors.affiliation: Light-Matter Interactions Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan.
authors.forename: Viet Giang
authors.initials: VG
authors.lastname: Truong
authors.affiliation: Institute for Theoretical Physics, University of Innsbruck, Technikerstrasse 25, A-6020, Innsbruck, Austria.
authors.forename: Helmut
authors.initials: H
authors.lastname: Ritsch
authors.affiliation: Light-Matter Interactions Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan.
authors.forename: Síle
authors.initials: S
authors.lastname: Nic Chormaic