  We present a study of the properties of the transversal "spin angular
momentum" and "orbital angular momentum" operators. We show that the "spin
angular momentum" operators are generators of spatial translations which depend
on helicity and frequency and that the "orbital angular momentum" operators
generate transformations which are a sequence of this kind of translations and
rotations. We give some examples of the use of these operators in light matter
interaction problems. Their relationship with the helicity operator allows to
involve the electromagnetic duality symmetry in the analysis. We also find that
simultaneous eigenstates of the three "spin" operators and parity define a type
of standing modes which has been recently singled out for the interaction of
light with chiral molecules. With respect to the relationship between "spin
angular momentum", polarization, and total angular momentum, we show that,
except for the case of a single plane wave, the total angular momentum of the
field is decoupled from its vectorial degrees of freedom even in the regime
where the paraxial approximation holds. Finally, we point out a relationship
between the three "spin" operators and the spatial part of the Pauli-Lubanski
four vector.
