Optical binding of particles with or without the presence of a flat dielectric surface - art. no. 035422

Optical fields can induce forces between microscopic objects, thus giving r ise to different structures of matter. We study theoretically these optical forces between two spheres, either isolated in water, or in the presence o f a flat dielectric surface. We observe different behavior in the binding f orce between particles at large and at small distances (in comparison with the wavelength) from each other. This is due to the great contribution of e vanescent waves at short distances. We analyze how the optical binding depe nds on the size of the particles, the material composing them, the waveleng th, and, above all, the polarization of the incident beam. We also show tha t depending on the polarization the force between small particles at small distances changes its sign. Finally, the presence of a substrate surface is analyzed, showing that it only slightly changes the magnitudes of the forc es, but not their qualitative nature, except when one employs total interna l reflection, in which case the particles are induced to move together alon g the surface.