Optical swimmers from asymmetric dumbbells

We explore the behaviour of optically driven microswimmers made from pairs of optically dissimilar spheres joined as dumbbells. When such a dumbbell is illuminated, simulations suggest there will be a lateral optical force along the dumbbell axis. We consider such dumbbells trapped in a high order Laguerre-Gaussian (LG) laser beam, both experimentally and computationally. The dumbbells were constructed from beads with two different refractive indices. It is found that the dumbbells move around the ring of the LG beam with an angular speed that depends on the orientation of the dumbbell in the trap. From the change in angular velocity when the sign of the OAM is reversed, the magnitude and direction of the lateral force component is determined.