ABSTRACT
The term spin-orbit interaction refers to the interaction and coupling of the spin and orbital degree of freedom of spinning particles such as electrons or other quantum particles. The universal nature of such interaction has led to its manifestation in diverse fields of physics, ranging from atomic, condensed matter to optical systems. In optics, the angular momentum (AM) of light is related to the circular (elliptical) polarization of light waves or the helical phase fronts (vortex) of optical beams. In classical electromagnetic description, the former is associated with the rotation of the electric field vector around the propagation axis and is referred to as the spin angular momentum (SAM); the latter is associated with rotation of the phase structure of a light beam and is known as orbital angular momentum (OAM). From a fundamental point of view, coupling and interconversion between the spin and orbital AM degrees of freedom of light are thus expected under certain circumstances, and accordingly the evolution of polarized light in a trajectory should mimic the SOI effect of a massless spin 1 particle (photon) (that is the SOI effects exhibited by spin 12 electrons while evolving under an external field). In this chapter, we address this issue and show that this effect can indeed be observed in a variety of light-matter interactions, e.g., by the tight focusing of fundamental or higher-order Gaussian beams, reflection/refraction of finite beams at dielectric interfaces, high numerical aperture imaging, scattering from micro-/nanosystems, propagation in gradient index media and so forth. We shall briefly address the various interesting manifestations of SOI, discuss corresponding mathematical frameworks (based on wave optics treatment) for describing SOI and provide illustrative examples of the resulting effects and
Wave Trends
discuss their potential implications. In this regard, we shall define SAM and OAM of light through classical electromagnetic (EM) wave optics formalism and introduce the concept of geometrical phase of light (the spin redirection Berry phase and Pancharatnam Berry phase), which is intimately related to the SOI of light.
