title: Escape trajectories of single-beam optically trapped micro-particles in a transverse fluid flow.
abstract: We have studied the transverse and axial equilibrium positions of dielectric micro-spheres trapped in a single-beam gradient optical trap and exposed to an increasing fluid flow transverse to the trapping beam axis. It is demonstrated that the axial equilibrium position of a trapped micro-sphere is a function of its transverse position in the trapping beam. Moreover, although the applied drag-force acts perpendicularly to the beam axis, reaching a certain distance r(0) from the beam axis (r(0)/a approximately 0.6, a being the sphere radius) the particle escapes the trap due to a breaking axial equilibrium before the actual maximum transverse trapping force is reached. The comparison between a theoretical model and the measurements shows that neglecting these axial equilibrium considerations leads to a theoretical overestimation in the maximal optical transverse trapping forces of up to 50%.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Merenda
authors.forename: Gerben
authors.initials: G
authors.lastname: Boer
authors.forename: Johann
authors.initials: J
authors.lastname: Rohner
authors.forename: Guy
authors.initials: G
authors.lastname: Delacrétaz
authors.forename: René-Paul
authors.initials: RP
authors.lastname: Salathé