  We derive exact expressions, in the form of Fourier integrals over the (k,w)
domain, for the energy, momentum, and angular momentum of a light pulse
propagating in free space. The angular momentum is seen to split naturally into
two parts. The spin contribution of each plane-wave constituent of the pulse,
representing the difference between its right- and left-circular polarization
content, is aligned with the corresponding k-vector. In contrast, the orbital
angular momentum associated with each plane-wave is orthogonal to its k-vector.
In general, the orbital angular momentum content of the wavepacket is the sum
of an intrinsic part, due, for example, to phase vorticity, and an extrinsic
part, r_CM x p, produced by the linear motion of the center-of-mass r_CM of the
light pulse in the direction of its linear momentum p.
