Orbital Angular Momenta and Geometric Phase Characteristics of Spin-polarized Components of a General Paraxial Beam-field

We explore a subtle and fundamental nature of spin-orbit interaction (SOI) in a general paraxial beam-field by mathematically characterizing the orbital angular momentum (OAM) flux densities of the spin-polarized component fields via Barnett's flux determination formalism. We show the application of our formalism by considering the special case of a Brewster-reflected paraxial beam, for which we explore specific details such as non-canonical vortex phase structures and single-photon interpretation of the field function. The phases of the spin-component fields are interpreted as geometric phases; and we devise an experimental method of direct measurement of these phases by transferring the spatial phase information to the polarization domain -- thus demonstrating a classical analog von Neumann measurement. Our complete mathematical characterization of SOI and its relevance to the direct measurement of geometric phase can find potential application in future methods exploring OAM and geometric phase characteristics in other general optical systems.