Using lasers, two researchers at the Hungarian Academy of Sciences have built and operated structures that work much like windmills. First, Pál Ormos and Péter Galajda used two-photon polymerization (see Physics Today, May 1999, page 9) to chemically carve rotors out of a resin-based material. Then, holding a free-floating rotor in optical tweezers, they used radiation pressure instead of wind to turn it at a speed dependent on the photon flux. They also manufactured other shapes for their devices, including helices and propellers. In the demonstration of light-powered micromachinery shown here, an optical rotor turned an interlinked cogwheel, each about 5 µm in diameter. In addition to providing torque to miniature devices, the rotors could be used to measure fluid properties on micron scales. Alternatively, it may be possible to study the mechanical properties of certain molecules, such as proteins or DNA, by fixing one end to a surface, attaching a rotor to the other end, and using light to apply a twisting force. (P. Galajda, P. Ormos, Appl. Phys. Lett. 78, 249, 2001 https://doi.org/10.1063/1.1339258 .)
