Optical angular momentum

Recent experiments show that both the spin and the orbital angular momentum
transferred to a small particle are proportional to the local intensity of
the beam. However it is well known that the predicted spin density in a light
beam within the Mawell formalism depends on the radial gradient of the
intensity. This gives rise to a controversy as the local sign of the spin
density can be different from the global polarization state of the beam. In
this work we clarify the relevance of local and global aspects in a
consistent treatment of the transfer of optical angular momentum to small
objects.