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26 August 2005 Pattern formation in evanescent wave optical traps
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Two counter-propagating laser beams incident at the silica-water interface above the critical angle set up interference fringes (with a spacing of 0.4-μm) in an evanescent wave. This paper describes the optical binding of sub-micron polystyrene spheres in the evanescent field. At low particle densities, the particles form lines perpendicular to the fringes; the particle positions may be commensurate or incommensurate with the fringes, depending on the particle size. At higher particle densities, well-ordered 2-D arrays form with a centred rectangular lattice in which the lattice constant in the plane of incidence is twice the fringe spacing. Rotating the plane of polarisation of one of the two laser beams eliminates the fringes, but ordered arrays still form. These arrays are either rectangular or pseudo-hexagonal depending on the particle size. A range of dynamical behaviour analogous to that of atomic crystals was observed.
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Christopher D. Mellor, Colin D. Bain, and John Lekner "Pattern formation in evanescent wave optical traps", Proc. SPIE 5930, Optical Trapping and Optical Micromanipulation II, 59301C (26 August 2005);

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