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. Author manuscript; available in PMC: 2019 Jan 1.
Published in final edited form as: Wiley Interdiscip Rev Nanomed Nanobiotechnol. 2017 Apr 24;10(1):10.1002/wnan.1477. doi: 10.1002/wnan.1477

Figure 1.

Figure 1

Optical trapping geometries. (a) A dielectric bead in a tightly focused beam near the focus of a microscope objective experiences an optical gradient force toward the focal point, and a scattering force that displaces the bead from the trap center. (b) Near the surface of a nanophotonic waveguide, a dielectric bead experiences an optical gradient force toward the surface due to the evanescent field decay. Light scattered by the trapped bead imparts a scattering force that can propel the bead along the waveguide. (c) The scattering force is eliminated by establishing a stationary standing wave in the waveguide.