An optical spin micromotor

An optical spin micromotor operated by optical tweezers, described in the p resent study, converts radiant energy directly to mechanical energy. This c onversion is of great practical and fundamental interest. The optical spin micromotor consists of a two-bead linkage. The large bead (2.0 mu m in diam eter) is trapped by the optical tweezers and rotates around the laser beam axis. The small bead (0.94 mu m in diameter) is partially coated with gold/ palladium for generating the spin torque through the change of momentum fro m gradient radiation pressure of the same laser applied on the coated small bead. With a laser power of 29 mW at the sample plane, the spin speed aver aged 158.8 +/- 155.5 rpm (mean +/- standard deviation) and the torque was e stimated as 101.9 +/- 99.8 pN nm. This optical spin micromotor will be usef ul in (1) providing a fundamental step toward developing optical-operated m echanical devices, (2) twisting macromolecules, and (3) generating vortex a nd shear force in medium at nanoscale. (C) 2000 American Institute of Physi cs. [S0003-6951(00)03913-9].