Spin and orbital angular momentum of a class of nonparaxial light beams having a globally defined polarization
- Department of Physics, Shanghai University, 99 Shangda Road, Baoshan District, 200444 Shanghai (China)
It is shown that the momentum density of free electromagnetic field splits into two parts. One has no contribution to the net momentum due to the transversality condition. The other yields all the momentum. The angular momentum that originates from the former part is spin, and the angular momentum that originates from the latter part is orbital angular momentum. Expressions for the spin and orbital angular momentum are given in terms of the electric vector in reciprocal space. The spin and orbital angular momentum defined this way are used to investigate the angular momentum of nonparaxial beams that are described in a recently published paper [Phys. Rev. A 78, 063831 (2008)]. It is found that the orbital angular momentum depends, apart from an l-dependent term, on two global quantities, the polarization represented by a generalized Jones vector and another characteristic represented by a unit vector I, though the spin depends only on the polarization. The polarization dependence of orbital angular momentum through the effect of I is obtained and discussed. Some applications of the result obtained here are also made. The fact that the spin originates from the part of momentum density that has no contribution to the net momentum is used to show that there does not exist the paradox on the spin of circularly polarized plane wave. The polarization dependence of both spin and orbital angular momentum is shown to be the origin of conversion from the spin of a paraxial Laguerre-Gaussian beam into the orbital angular momentum of the focused beam through a high numerical aperture.
- OSTI ID:
- 21352433
- Journal Information:
- Physical Review. A, Vol. 80, Issue 6; Other Information: DOI: 10.1103/PhysRevA.80.063814; (c) 2009 The American Physical Society; ISSN 1050-2947
- Country of Publication:
- United States
- Language:
- English
Similar Records
Orbital angular momentum of general astigmatic modes
Angular momenta and spin-orbit interaction of nonparaxial light in free space