Figure 4

(a) Schematic configuration of a pair of optically bound particles near the dielectric mirror and illustration of the intensity lobes created by interference of the tractor beam and the field scattered by particle 1. (b) Calculated velocities (triangle length proportional to the square root of the pair speed) of stable 820-nm sphere pairs for the S- and P-polarized beams incident at an angle of α=2.82°. The distance y_M of particle 1, which is placed at the coordinate origin, from the dielectric mirror is ∞, 16 and 9.6 μm (close to the experimental value). The background denotes the electric field density calculated as in Figure 3a, the scattered field is taken as the sum of the field scattered by particle 1, its mirror image 1’, and the mirror image of the particle 2’, shown in c. The green and yellow shadings correspond to the smaller and larger observed inter-particle distance in d, respectively. (d) Experimental observations of the stable positions of the centers of particle pairs near the dielectric mirror for the S- and P-polarized tractor beams.