Yoshihiko Arita, Mingzhou Chen, Ewan M. Wright, and Kishan Dholakia

Journal of the Optical Society of America B 34(6), C14-C19 (2017)

doi: 10.1364/JOSAB.34.000C14

We trap a single silica microparticle in a complex three dimensional optical potential with orbital angular momentum in vacuum. The potential is formed by the generation of a “perfect vortex” in vacuum which, upon propagation, evolves to a Bessel light field. The optical gradient and scattering forces interplay with the inertial and gravitational forces acting on the trapped particle, to produce a rich variety of orbital motions with respect to the propagation axis. As a result the particle undergoes a complex trajectory, part of which is rotational motion in the plane of the “perfect vortex”. As the particle explores the whole three dimensional volume and is not solely restricted to one anchor point, we are able to determine the three dimensional optical potential in situ by tracking the particle. This represents the first demonstration of trapping a microparticle within a complex three dimensional optical potential in vacuum. This may open up new perspectives in levitated optomechanics with particle dynamics on complex trajectories.