Escape trajectories of single-beam optically trapped micro-particles in a transverse fluid flow

Fabrice Merenda, Gerben Boer, Johann Rohner, Guy Delacrétaz, René-Paul Salathé
2006 Optics Express  
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
more » ... e beam axis (r 0 /a 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%.
doi:10.1364/oe.14.001685 pmid:19503495 fatcat:aykl5j7ilvf7xg4irmqrmenxa4