Dynamics of Optically Levitated Microdumbbells

Abstract

As light carries momentum, enough force can be applied to small particles from a vertical pointing laser to counteract the gravitational force it feels, thus levitating it in thin air. Oblong nanoparticles under these conditions have shown themselves to align their long axis with the laser’s polarization and rotate with it. The precise torque control and measurements these levitated objects offer are hypothesised to pave way for future quantum development. Previous experiments have also created the fastest man made rotor at 1 GHz, which was achieved by a levitated nanodumbbell in circularly polarized light. However, the behavior of these levitated oblong objects with regards to polarization is not as well known at bigger scales. Here we have studied how polarization affects micrometric dumbbells. We found a direct connection between the dumbbells’ elevation in the trap and their reaction to the polarization, giving rise to different regimes. Furthermore, under circularly polarized light we showed a cyclical process where a dumbbell would start to oscillate and rise in elevation in the trap. At a certain point, this oscillation would fade and the particle would fall down in the trap and repeat the same steps. Our results show a clear difference between dumbbells at nanoscale compared to microscale, with models presented to explain the different behaviors. Many of the phenomena that we have observed may serve as a subject of future research. These phenomena include dumbbell turnovers, exploring the dumbbell’s alignment in the stationary regime and finding a theoretical explanation for the different regimes of dumbbell-polarization interaction.