  Optical tweezers use light from a tightly focused laser beam to manipulate
the motion of tiny particles. When the laser light is strongly focused, but
still paraxial, its e/m field is characterized by a longitudinal component
which is of magnitude comparable to the transverse ones and which has been
ignored in the theoretical analysis of the tweezing forces. In our work we
revise the calculations of the various components of the radiation pressure
force, within the limits of Rayleigh regime or dipole approximation, in the
case where a tiny particle interacts, in free space, with a circularly
polarized optical vortex beam, by taking into account this ignored field term.
We show that this term is responsible for considerable modifications in the
magnitude of the various components, moreover and also for the appearance of
terms involving the coupling of the spin angular momentum (SAM) and the orbital
angular momentum (OAM) of the photons of the vortex beam. We compare our
findings with the ones taken ignoring the longitudinal field component.
