Fig. 4. Study on the horizontal migration characteristics of TOTs by DFLs.

a Schematic diagram of the horizontal migration of PS particles controlled by DFLs with varying optical powers. b Trapping force distributions with an optical power ratio of 0.36:1. The color bar indicates the amplitude, and the arrows denote the directions of the trapping force. c Axial trapping force curves on the x axis for different optical power ratios. d Particle displacement in the x axis over time. e Migration of the PS particle in the horizontal direction is achieved by alternating the optical powers. The combined power of the two lasers is 14.6 mW. f Schematic illustration of the horizontal migration of a single particle through adjustable-spacing DFLs on a single-track PTW. g Trapping force distributions on the x‒y plane for DFL spacings of D = 20, 42, and 69 μm. The purple dots symbolize the lasers. The white dotted circles indicate PS particles trapped in the force potential wells. The color bar indicates the amplitude, and the arrows denote the directions of the trapping force. h Experimental results of a PS particle trapped by TOT with varying DFL spacings. x₀ denotes the horizontal distance of the particle from the PTW. i Displacement x₀ of the particle and spacing D of the DFLs varying with time. Each focused laser has an incident power of 11.1 mW. Scale bar: 25 μm