Optically controlled three-dimensional rotation of microscopic objects

We demonstrate that microscopic objects held in optical tweezers can be set into controlled rotation about any axis of choice. Our approach relies on the use of a spatial light modulator to create a pair of closely separated optical traps holding different parts of the same object. The pair of traps can be made to revolve around each other in any plane, rotating the trapped object with them. This technique overcomes the previous restriction on the orientation of the rotation axis to be parallel to the beam axis, and extends the versatility of optical tweezers as micromanipulation tools. (C) 2003 American Institute of Physics.