Influence of nonconservative optical forces on the dynamics of optically trapped colloidal spheres: the fountain of probability.
We demonstrate both experimentally and theoretically that a colloidal sphere trapped in a static optical tweezer does not come to equilibrium, but rather reaches a steady state in which its probability flux traces out a toroidal vortex. This nonequilibrium behavior can be ascribed to a subtle bias of thermal fluctuations by nonconservative optical forces. The circulating sphere therefore acts as a Brownian motor. We briefly discuss ramifications of this effect for studies in which optical tweezers have been treated as potential energy wells.
Roichman
Yohai
Y
Department of Physics and Center for Soft Matter Research, New York University, New York, NY 10003, USA.
Sun
Bo
B
Stolarski
Allan
A
Grier
David G
DG