Rotors produced and driven in laser tweezers with reversed direction of rotation

Micrometer size rotors are produced by light induced polymerization of light curing resin. The propeller shaped rotors trapped in laser tweezers are rotated by the trapping light. A rotor is built that changes the direction of rotation by changing its position relative to the focus. The design is based on the very high numerical aperture of the focused light in the tweezers: the light has a large average component of momentum pointing perpendicular to the optical axis, in the opposite direction before and behind the focus. This perpendicular component drives the rotation and the direction changes when the rotor is moving around the focus.