Optical Vortex Ladder via Sisyphus Pumping of Pseudospin

Abstract: Robust higher-order optical vortices are much in demand for applications in optical manipulation, optical communications, quantum entanglement and quantum computing. However, in numerous experimental settings, a controlled generation of optical vortices with arbitrary orbital angular momentum (OAM) remains a substantial challenge. Here, we present a concept of "optical vortex ladder" for stepwise generation of optical vortices through Sisyphus pumping of pseudospin modes in photonic graphene. Instead of conical diffraction and incomplete pseudospin conversion under traditional Gaussian beam excitations, the vortices produced in the ladder arise from non-trivial topology and feature diffraction-free Bessel profiles, thanks to the refined excitation of the ring spectrum around the Dirac cones. By employing a periodic "kick" to the photonic graphene, effectively inducing the Sisyphus pumping, the ladder enables tunable generation of optical vortices of any order even when the initial excitation does not involve any OAM. The optical vortex ladder stands out as an intriguing non-Hermitian dynamical system, and, among other possibilities, opens up a pathway for applications of topological singularities in beam shaping and wavefront engineering.