Effect of orbital angular momentum on photonic spin Hall effect in a rovibrational optical cavity

We investigate the influence of orbital angular momentum (OAM) on the optical response of an intracavity rovibrational optomechanical system interacting with a weak probe field. In the absence of OAM, the system exhibits a well-resolved optomechanically induced transparency (OMIT) window at zero detuning, accompanied by strong photonic spin Hall effect (SHE) shifts. Introducing non-zero OAM activates rotational degrees of freedom, leading to rovibrational mode hybridization and the emergence of multiple transparency dips in the absorption spectrum. As the OAM increases, the absorption profile evolves from a single window to multiple split and broadened transparency regions, indicating strengthened coupling between rotational and vibrational modes. However, the photonic SHE response does not scale monotonically with OAM. While low OAM values degrade the photonic SHE due to dispersion flattening and phase gradient suppression, higher OAM values can recover or even amplify the spin-dependent shift under specific detuning conditions. This recovery stems from enhanced hybridization and sharper phase gradients near broadened transparency windows. Density plots of the photonic SHE shift versus OAM and incidence angle reveal a nontrivial interplay between light’s angular momentum and the spin–orbit interaction, showing that field localization, detuning, and phase dispersion jointly govern the system’s light-steering capabilities. Notably, the probe field starts and ends as a Gaussian beam, and OAM is introduced parametrically via cavity-mediated interaction and not through a vortex phase front imposed on the input beam. Thus, the reflected intensity distribution remains Gaussian-shaped, but its centroid (spin-dependent) is influenced by the OAM-controlled changes that lead to a modified photonic SHE shift. These findings highlight the tunability of intracavity optomechanical systems via OAM for applications in optical sensing, spin-controlled photonics, and structured light–matter interactions.