Optically driven liquid crystal rotator

Rotation of nematic liquid crystal (NLC) droplets by irradiation of focused circular polarized light is experimentally studied. Optical torque transferred to a droplet depends on its size. We discuss the relation between the LC molecular alignment inside the droplet and its rotation mechanism. In a larger droplet, the internal LC alignment is bipolar and wave-plate behavior becomes dominant. In a smaller droplet, the optical anisotropy reduces with decrease of its size and scattering process mainly contributes its rotation. We also construct multiple LC rotators system using a holographic optical tweezer. Such optically controllable vortex enables us to realize complex flow field at micron-scale.