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Proceedings Paper

Non-conservative forces in optical tweezers and Brownian vortexes
Author(s): Bo Sun; Alexander Y. Grosberg; David G. Grier
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Paper Abstract

Mechanical equilibrium at zero temperature does not necessarily imply thermodynamic equilibrium at finite temperature for a particle confined by a static, but non-conservative force field. Instead, the diffusing particle can enter into a steady state characterized by toroidal circulation in the probability flux, which we call a Brownian vortex. The circulatory bias in the particle's thermally-driven trajectory is not simply a deterministic response to the solenoidal component of the force, but rather reflects an interplay between advection and diffusion in which thermal fluctuations extract work from the non-conservative force field. As an example of this previously unrecognized class of stochastic machines, we consider a colloidal sphere diffusing in a conventional optical tweezer. We demonstrate both theoretically and experimentally that non-conservative optical forces bias the particle's fluctuations into toroidal vortexes whose circulation can reverse direction with temperature or laser power.

Paper Details

Date Published: 8 February 2010
PDF: 6 pages
Proc. SPIE 7613, Complex Light and Optical Forces IV, 76130A (8 February 2010); doi: 10.1117/12.839922
Show Author Affiliations
Bo Sun, New York Univ. (United States)
Alexander Y. Grosberg, New York Univ. (United States)
David G. Grier, New York Univ. (United States)

Published in SPIE Proceedings Vol. 7613:
Complex Light and Optical Forces IV
Enrique J. Galvez; David L. Andrews; Jesper Glückstad, Editor(s)

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