Fig. 2

Experimental determination of optical torque crossover as a function of optical matter array size. a Sequences of optical images of a 3-I array and a 10-I array in a LHCP laser beam. The time interval between frames is 0.01 s for the 3-I array and 0.033 s for the 10-I array. The two arrays clearly exhibit opposite rotation directions as indicated by following the × symbols although they are illuminated with the same LHCP optical beam. The scale bar is 1 µm. b Trajectories of four different optical matter arrays relative to the center of mass of each array for 2 s. The open circles are representative instantaneous configurations. c Time trajectories of orientations of individual NPs in each array relative to its center of mass. The central particle in the 7-I array overlaps with the center of rotation and therefore is not shown. d Average angular velocity of optical matter arrays as a function of the number of particles in each array. The colored symbols delineate type-I, II, III structures (see Fig. 1 for examples). The insets are optical images of two special arrays with 9 NPs, where the only difference is the position of one NP-indicated by the green circle. e The mean values of all nearest neighbor distances of different arrays. Error bars in d and e correspond to one standard deviation