Laser beams have been demonstrated to be capable of exerting torque as well as forces on microparticles. Using a custom magneto-optic manipulator, we directly measured the torque exerted by laser light on absorbing microspheres as a result of the transfer of spin angular momentum. A general method for measuring torque has been developed, and the experimental apparatus has shown a sensitivity of ∼1 pN/nm .
© 2004 Optical Society of America
(140.7010) Lasers and laser optics : Laser trapping
(170.4520) Medical optics and biotechnology : Optical confinement and manipulation
(230.3810) Optical devices : Magneto-optic systems
(230.5440) Optical devices : Polarization-selective devices
(260.2160) Physical optics : Energy transfer
Marco Capitanio, Davide Normanno, and Francesco Saverio Pavone, "High-precision measurements of light-induced torque on absorbing microspheres," Opt. Lett. 29, 2231-2233 (2004)