Microstructures created and driven by light

Principal Investigator: Pál Ormos
This project is part of the EU-FP6 cooperation ATOM-3D

The momentum carried by light can exert torque on microscopic propellers. These light driven rotors work similar to windmills: a particle flow (wind/photon flow) is deflected by an object (windmill/micropropeller), upon deflection the particles exert force and torque on the deflecting object.



The rotation direction of windmills (propellers) is determined by their shape. However, the windmill analogy has its limits: wind actually corresponds to a collimated light beam, i.e. momentum carried by the whole beam points in one direction. On the other hand, in the case of an optical trap a high NA focused light holds and drives the rotor. This light has large momentum component perpendicular to the propagation, and this component changes direction before and after the focus. We prepared microrotors by photopolymerisation that are driven by this momentum component perpendicular to the direction of propagation. Depending on whether it is placed before or after the focus, it changes the direction of rotation.



Click here to view a video of the experiment.

Reference:
P. Galajda and P.l Ormos, Rotors produced and driven in laser tweezers with reversed direction of rotation, Appl. Phys. Lett. 80, 4653-4655 (2002).