title: Self-propelled round-trip motion of Janus particles in static line optical tweezers.
abstract: Controlled propulsion of microparticles and micromachines in fluids could revolutionize many aspects of technology, such as biomedicine, microfluidics, micro-mechanics, optomechanics, and cell biology. We report the self-propelled cyclic round-trip motion of metallo-dielectric Janus particles in static line optical tweezers (LOT). The Janus particle is a 5 μm-diameter polystyrene sphere half-coated with 3 nanometer thick gold film. Both experiment and theory show that this cyclic translational and rotational motion is a consequence of the collective and fine action of the gold-face orientation dependent propulsion optical force, the gradient optical force, and the spontaneous symmetry breaking induced optical torque in different regions of the LOT. This study indicates a novel way to propel and manipulate the mechanical motion of microscopic motors and machines wirelessly in fluid, air, or vacuum environments using a static optical field with a smartly designed non-uniform intensity profile allowing fully controlled momentum and angular momentum exchange between light and the particle.
authors.affiliation: Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.affiliation: School of Physics, South China University of Technology, Guangzhou 510640, China. phzyli@scut.edu.cn phhlguo@scut.edu.cn.
authors.forename: Hong-Lian
authors.initials: HL
authors.lastname: Guo
authors.affiliation: School of Physics, South China University of Technology, Guangzhou 510640, China. phzyli@scut.edu.cn phhlguo@scut.edu.cn and Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Zhi-Yuan
authors.initials: ZY
authors.lastname: Li