Optical tweezers can trap and move materials noninvasively at length scales ranging from tens of nanometers to tens of micrometers, and so have provided unprecedented access to physical, chemical and biological processes on a microscale. Since a light beam can carry angular momentum.

(AM) it is possible to use optical tweezers to exert torques to twist or rotate microscopic objects. Spin angular momentum depends on the degree of circular polarisation of the light, and orbital angular momentum depends on the spatial structure of the beam. If either the spin or orbital angular momentum is altered when the trapping beam is scattered by the particle in the trap, an optical torque will result. Further, it is relatively easy to simultaneously measure optically the torque being exerted, without the need for any elaborate calibration procedure. These optical rotators provide fine orientation control and using these techniques, the mechanical properties of cells can be usefully studied.

These methods could also easily find applications in biotechnology and micromechanics. We use these methods to align and rotate microparticles and have demonstrated the use of this type of rotation for microviscosity measurements.

Seminar, March 29, 12:00h. Conference Room