Orientation of flat particles in optical tweezers by linearly polarized light

Micrometer-sized objects with flat shapes have been oriented in optical tweezers formed by polarized light. The orienting torque originates from the anisotropic scattering of polarized light by the trapped particle. We investigated this effect experimentally on objects produced by photopolymerization. We determined and characterized the orienting torque acting on these particles, and the results were interpreted by model calculations. By manipulating particles with appropriately shaped optical tweezers, we can fully control the position of the particle in the trap. The torque exerted on the object can be measured and controlled. This angular trapping effect offers a useful extension of optical tweezer applications.