Regensburg 2004 – wissenschaftliches Programm

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DY: Dynamik und Statistische Physik

DY 46: Poster

DY 46.30: Poster

Donnerstag, 11. März 2004, 16:00–18:00, Poster D

Dynamics of colloidal particles in a toroidal optical trap — •Michael Reichert and Holger Stark — Universität Konstanz, Fachbereich Physik, D-78457 Konstanz, Germany

A theoretical study of the collective non-Brownian motions of colloidal particles circulating in a toroidal trap is presented. We consider equal-sized spheres in the regime of low Reynolds numbers whose interactions are solely of hydrodynamic origin. The concrete physical situation we have in mind are optical vortices, i.e., focussed helical light modes carrying an orbital angular momentum [1]. We mimick this in our simulations by applying a tangential driving force and a harmonic radial trap force on each particle.

The orbital velocities of the circulating particles depend on the particle number and the ring radius. We analyze them for different arrangements, e.g., regular symmetric or random configurations. It turns out that the random configurations lead effectively to a higher velocity compared to the regular arrangements due to “drafting” effects.

Furthermore, we study the time-dependent dynamics of the random configurations. The simulations show that, after an irregular transient regime, the system tends towards a periodic dynamic state of oscillating particle distances. During this synchronisation process, the viscous drag is lowered.

[1] J. E. Curtis, D. G. Grier, Phys. Rev. Lett. 90, 133901 (2003).