Figure 3
From: Tailoring Optical Gradient Force and Optical Scattering and Absorption Force

Conservative optical force acting on a 1 micron diameter particle. The particle in water is illuminated by a standing wave as depicted in panel (d). (a) Potential Energy U. (b) |F g |. (c) |F k |. Clearly |F k | ≈ 0, therefore the force is conservative. (d) Schematic illustration for the configuration of the incident plane waves.