Optical angular momentum transfer to laser-trapped particles

Summary form only given. We study the transfer of "orbital" angular momentum from a linearly polarized Laguerre-Gaussian mode laser beam to absorbing particles. Micron-sized CuO particles were trapped in a focused "donut" beam, and observed to rotate when viewed through an optical microscope. The measurements show that an absorbing particle trapped and rotating in a focused plane-polarized laser beam rotates faster (slower) if the beam is changed to circularly polarized with spin of the same (opposite) sense as the helicity of the doughnut. The magnitude of the change in rotation frequency agrees with that expected from theory within the accuracy of the experiment.