MECHANICAL EQUIVALENCE OF SPIN AND ORBITAL ANGULAR-MOMENTUM OF LIGHT - AN OPTICAL SPANNER

We use a Laguerre-Gaussian laser mode within an optical tweezers arran gement to demonstrate the transfer of the orbital angular momentum of a laser mode to a trapped particle. The particle is optically confined in three dimensions and can be made to rotate; thus the apparatus is an optical spanner. We show that the spin angular momentum of +/- (h) over bar per photon associated with circularly polarized light can add to, or subtract from, the orbital angular momentum to give a total an gular momentum. The observed cancellation of the spin and orbital angu lar momentum shows that, as predicted, a Laguerre-Gaussian mode with a n azimuthal mode index l = 1 has a well-defined orbital angular moment um corresponding to (h) over bar per photon. (C) 1997 Optical Society of America