Object jumps between optical traps in co-propagating Bessel beams

Due to the co-propagation of both beams the radiation pressure pushes the objects axially along beams propagation or the fluid flow does the same in opposite direction. Depenting on the magnitudes of both effects the objects are pushed out of the intensity maximum. This causes that the barriers between neighboring traps on the left and right are not of the same dephts. Therefore the objects tend to jump more frequently over the smaller barrier and so the prefered jump direction is established. We used fast CCD camera to observe dynamics of these jumps from perpendicularly scattered light of the trapping beams.

Analyses of the jumps from the second movie are shown in the following figure. The dashed vertical lines denotes the boundary between neighboring traps. They were found from the histograms of beads positions (top plot). Once we knew the position of the trap boundaries, we looked for times when the object passed through this boundary. This event is shown in the lower plots by crossed circles with the corresponding time on the vertical axis. All the boundary crossings were connected by lines with the same slope found from a fit (blue dotted lines). Inverted value of this slope gave the velocity of the hops (excitement) spreading over the colloidal system.

More details can be found in the papers:

T. Cizmar, V. Kollarova, Z. Bouchal, P. Zemanek: "Sub-micron particle organization by self-imaging of non-diffracting beams",
       New Journal of Physics 8, 43:1-23, 2006,  LINK TO JOURNAL  ABSTRACT   DOWNLOAD MULTIMEDIA

T. Cizmar, V. Kollarova, M. Siler, P. Jakl, Z. Bouchal, V. Garces-Chavez, K. Dholakia, P. Zemanek: "Non-diffracting beam synthesis used for optical trapping and delivery of sub-micron objects",
       Proceedings of SPIE 6195, 619507:1-7, 2006, Nanophotonics, Strasbourg(FR), 3-5 Apr 2006,   ABSTRACT       DOWNLOAD

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