Rotation Detection in Light-Driven Nanorotors

We analyze the rotational dynamics of light driven nanorotors, made of nanotube bundles and gold nanorods aggregates, with nonsymmetric shapes, trapped in optical tweezers. We identify two different regimes depending on dimensions and optical properties of the nanostructures. These correspond to alignment with either the laser-propagation axis or the dominant polarization direction, or rotational motions caused by either unbalanced radiation pressure or polarization torque. By analyzing the motion correlations of the trapped nanostructures, we measure with high accuracy both the optical trapping parameters and the rotation frequency induced by the radiation pressure. Our results pave the way to improved all-optical detection, control over rotating nanomachines, and rotation detection in nano-optomechanics.