Figure 2.

Optical trapping by structured beams. (a) Distribution of the optical force along the wave axis of a silver nanoparticle at 400 nm. The inset shows the region of the NOF. (b) The optical force on a polystyrene sphere by a Bessel beam. Optical pulling force is possible for different radii of polystyrene particles. (c) The longitudinal forces F_z and radial forces F_r with a change in the radial distance between the particle and beam axis. The shaded region represents a stable pulling effect due to F_z<0 and F_r<0. Objects near the axis are confined by the gradient force and are transported in the propagation direction by the scattering force. (d) Polystyrene particles with radii of 800 and 1000 nm are separated by an s-polarized beam. Figure a reprinted with permission from Ref. 20, © 2010 Optical Society of America, b from Ref. 85, © 2011 Nature Publishing Group, c from Ref. 22, © 2011 American Physical Society, and d from Ref. 24, © 2013 Nature Publishing Group.