No abstract

In this paper, generalizations of the Stokes parameters and alternative characterizations of three-dimensional ͑3D͒ time-varying electromagnetic fields is introduced. One of these characteristics is the normal of the polarization plane, which, in many cases of interest, is parallel ͑or antiparallel͒ to the direction of propagation. Others are the two spectral density Stokes parameters which describe spectral intensity and circular polarization. The analysis is based on the spectral density tensor. This tensor is expanded in a base composed of the generators of the SU͑3͒ symmetry group, as given by Gell-Mann and Y. Ne'eman ͓The Eight-fold Way ͑Benjamin, New York, 1964͔͒ and the coefficients of this expansion are identified as generalized spectral density polarization parameters. The generators have the advantage that they obey the same algebra as the Pauli spin matrices, which is the base for expanding the 2D spectral density tensor with the Stokes parameters as coefficients. The polarization parameters introduced are formulated in the frequency domain, thereby further generalizing the theory to allow for wide-band electromagnetic waves in contrast to the traditional quasimonochromatic formulation.

[1] Novel measurement and approximation methodologies for studying orbital angular momentum (OAM) modes in radio beams, i.e., electromagnetic beam modes having helical phase fronts, are presented. We show that OAM modes can be unambiguously determined by measuring two electric field components at one point, or one electric field component at two points.