Abstract
We derive exact expressions, in the form of Fourier integrals over the (k,ω) 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 -vector. In contrast, the orbital angular momentum associated with each plane-wave is orthogonal to its -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, × p, produced by the linear motion of the center-of-mass of the light pulse in the direction of its linear momentum p.
- Received 13 June 2011
DOI:https://doi.org/10.1103/PhysRevA.84.033838
©2011 American Physical Society