Rotation of microscopic discs by the angular momentum of light

While the behavior of spherical particles confined in light beams is well-studied, the dynamics of confined non-spherical particles may be qualitatively different, but remain largely unexplored. We studied the rotation of microscopic dielectric discs induced by the incident angular momentum of an elliptically polarized Laguerre-Gaussian beam. These flat particles are confined in three dimensions by the beam and are oriented naturally with its long axis along the direction of the propagation of the beam. Due to the rotationally asymmetric shape of the particles, we were able to induce a constant rotation of the particles and control it by changing the vorticity and ellipticity of the beam. We also showed a strong dependence on the induced rotation respect to size of the particles. These results provide a new approach to generate or study flows in the microscopic realm as an alternative to the former techniques based on birefringent, absorbent or chiral particles.