Optically driven birefringent rotators

We use circularly polarized light to induce stable rotation in hundreds of colloidal micro-particles simultaneously. The optical angular momentum transferred to the particles creates a torque causing particle rotation. In the past, optical tweezers were used to rotate individual colloids while trapping them to the narrow waist of the focused beam. We use a defocused, circularly-polarized, beam to rotate multiple particles with minimal trapping. We developed a process for synthesizing stable birefringent vaterite particles that can rotate for long periods of times and characterized their optical and physical properties. Altering the handedness and intensity of the laser source allows us to control the frequency and switch between clockwise or counterclockwise rotation. We observe and discuss the interaction between the rotating particles.