Fig. 3: FDTD simulation results for different shaped particles.

a Sectional view of particles used in the simulations. Particle i represents an ideal sphere with radius of 0.1 μm; particles ii-iv are rough spheres modeled by varying radius values, which converge in distribution to a Gaussian variable with mean 0.1 μm and standard deviation σ = 1, 2 and 3 nm, respectively; particles v and vi are dimers composed of dual spheres with radius of 0.05 and 0.1 μm, respectively. b LOT as a function of the orientation angle α of the spherical particles i-iv. The angle is defined with respect to x-axis, as illustrated by the inset. c Calculated angular potential for the particles i-iv. d LOT and its conservative and nonconservative components versus the orientation angle of the dimer v. e A similar plot for the dimer vi. f Angular potential for v and vi. In all simulations, the particles are illuminated by the travelling wave (case I) in Fig. 2a, and are placed at a fixed position x = 0.35 λ, where the momentum curl of illumination reaches the maximum.