Transfer of orbital angular momentum to metal particles confined using optical tweezers

Using Laguerre-Gaussian beams in an inverted optical tweezers geometry we observe that silver particles, 2 mum in diameter, are confined to an annulus around the outside of the beam. This annulus is situated 4 mum below the beam waist where the upward scattering force counterbalances gravity. The scattering force results in a transfer of the orbital angular momentum content of the beam to the particle causing it to rotate about the beam axis.