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Experimental setup. Linearly polarized beam (IPG, 10 W, ) passed through half wave plate and was divided by a polarization beam-splitter PBS1 into two paths with controllable power ratio. The first -polarized beam is reflected on metallic mirror M1, transformed to the BB by an axicon A1 (Eksma 130-0270). The core of this BB is decreased by a telescope T1 formed by lens L1 and microscope objective O1 (Newport, M-40X, N.A. 0.40). The second -polarized beam is reflected on the metallic mirror M2 and on a polarization beam-splitter PBS2, passed through the quarter wave plate to the axially movable mirror M3 controlled by stepmotor (Newport ESP 300), reflected back through the same (the beam became polarized) and transformed to the BB by an axicon A2 (Eksma 130-0260) and narrowed down by T2 made from lens L2 and microscope objective O2 (Newport, M-20x, N.A. 0.40). Both BBs interfere with the cuvette C. The particles in the cuvette are observed by a microscope objective with long working distance LDO (Mitutoyo MPlan NR50) and CCD camera.
Demonstration of an optical microconveyor delivering two polystyrene spheres of 410 nm diameter over a distance using a sliding Bessel standing wave.
The theoretical dependence of the extremal (maximal or minimal) axial optical force (top plot) and trap depths (bottom plot) in the Bessel standing wave as a function of polystyrene beads diameter. Particles were confined in using on-axis optical intensity in each beam (equivalent to on-axis intensity in Gaussian beam of beam waist and power 1 W) of the idealized Bessel beam created by the same optics as in the experiment. The negative values of extremal forces indicates that the bead is trapped with its center at the node of the SW. Stars denote the bead sizes used in experiments. Vertical dotted lines indicate bead sizes that do not feel the Bessel standing wave and therefore cannot be confined in this periodic structure (see Ref. 10).
Comparison of the ratio of longitudinal and lateral stiffnesses obtained from the theory (the same parameters as in Fig. 3) and experiment. The error bars correspond to the 90% confidence level. Insets show the record of positions of single polystyrene bead of diameters 410 nm (over a period of 166 s) and 490 nm (over 127 s) confined in Bessel standing wave.
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