Drying-mediated optical assembly of silica spheres in a symmetrical metallic waveguide structure.

We describe the optical trapping application of a simple metallic slab optical waveguide structure, and demonstrate the influence of the excited guided modes on the aggregation behavior of silica particles during the irreversible evaporation process. Periodic horizontal stripes are formed by the highly ordered assemblies of the silica spheres, which is explained via the interference effect between the forward propagating modes and its reflection at the solvent surface. Particularly, several layers consisting of high-density particles are discernible in the stripe zones due to the optical binding, while no particles locate between these stripes. Completely different from the self-assembly patterns in the evaporating solvent without excitation of optical modes, this Letter demonstrates the versatility in the possible patterns of the optical assembly by a coupling waveguide with more complex structures.