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Optical binding has been proposed to be responsible for the cluster formation of micron size dielectric spheres in coherent light fields. However, a direct measurement of the forces involved in binding is missing. We report an experimental study of optical binding forces between two optically trapped dielectric spheres. Results for optical forces are presented as a function of three parameters: inter particle separation, particle size, and respective polarizations. A comprehensive calculation based on the generalized Mie scattering theory for the experiment has also been conducted. This paper will present a comparison between experimental and theoretical results.
A schematic illustration of the experimental procedure. The directions of the electric field polarization are in the direction perpendicular (the Y-Y configuration) shown in the left or parallel (the X-X configuration) to the direction along the x axis which is the direction of the separation of the two particles
The optical binding force data shows the force of optical binding between two 1.5μm polystyrene particles trapped in separate quadratic potential wells each made from polarized s-wave 72mW 1064nm laser beams, as function of the interparticle separation. The experiments (right) and simulations (left) for two particles moved along the perpendicular direction with the laser beam polarization were shown in black; along the direction parallel to the laser beam polarization were shown in red.
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