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.
Department of Physics and Center for Soft Matter Research, New York University, New York, NY 10003, USA.
Yohai
Y
Roichman
Bo
B
Sun
Allan
A
Stolarski
David G
DG
Grier