Sub-micron particle organization by self-imaging of non-diffracting beams

Abstract

We present the first theoretical and experimental study of dielectric sub-micron particle behaviour in an optical field generated by interference of co-propagating non-diffracting beams of different propagation constants. In such a field, there are periodic oscillations of the on-axial intensity maxima (self-imaging) that are frequently mentioned as useful for optical trapping. We show that in three dimensions this is true only for very small particles and the increasing number of interfering beams does not enable confinement of substantially bigger particles under the studied conditions. Experimentally, we succeeded in optical confinement of beads radii from 100 nm up to 300 nm but only with the help of fluid flow against the beams propagation. We observed self-organization of the particles into the periodic 1D array with the interparticle distance equal to 7.68 μm. We observed how a bead jump from one trap to the neighbouring-occupied trap caused a domino effect propagating with constant velocity over the subsequent occupied traps. Phase shift in one beam induced controlledbi-directional shift of the whole structure over a maximal distance of 250 μm in two co-propagating Bessel beams.