In condensed matter, the spin Hall effect refers to the spin-dependent deflection of electron trajectories, caused by spin-orbit coupling. This phenomenon has an optical counterpart, involving the coupling between circular polarization and the orbital angular momentum of a light beam. Such coupling naturally occurs in inhomogeneous media, typically at dielectric interfaces. In 2019, we demonstrated that non-paraxial light beams propagating through transverse spatial disorder exhibit a spin Hall effect [Bardon-Brun, Delande, Cherroret, Phys. Rev. Lett. 123, 043901 (2019)]. The figure on the right illustrates a beam incident on a dielectric with transverse (x,y) refractive index disorder (but no z-axis disorder). For oblique incidence, we showed that the beam undergoes a helicity-dependent lateral shift during propagation. The effect vanishes in the absence of disorder or for linearly polarized beams. This finding, which was the focus of Tamara Bardon-Brun’s PhD, has led to further studies in correlated disordered media [Carlini, Cherroret, Phys. Rev. A 105, 053508 (2022)] and photonic lattices [Carlini, Cherroret, SciPost Phys. 14, 104 (2023)], explored during Federico Carlini’s PhD.
This discovery is significant because it reveals a novel connection between spin-orbit interactions of light and wave propagation in complex media. Fundamentally, it may enable optical simulations of spin-orbit interactions in condensed matter, and practically, it offers a way to control light propagation in complex media via polarization.
