title: Mechanical equivalence of spin and orbital angular momentum of light: an optical spanner.
abstract: We use a Laguerre-Gaussian laser mode within an optical tweezers arrangement 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 +/-?per photon associated with circularly polarized light can add to, or subtract from, the orbital angular momentum to give a total angular momentum. The observed cancellation of the spin and orbital angular momentum shows that, as predicted, a Laguerre-Gaussian mode with an azimuthal mode index l=1 has a well-defined orbital angular momentum corresponding to ? per photon.
authors.forename: N B
authors.initials: NB
authors.lastname: Simpson
authors.forename: K
authors.initials: K
authors.lastname: Dholakia
authors.forename: L
authors.initials: L
authors.lastname: Allen
authors.forename: M J
authors.initials: MJ
authors.lastname: Padgett