Large Optical Lateral Force with a Phase-Engineered Photonic Spin Hall Effect

Abstract

The photonic spin Hall effect (PSHE) manifests as a spin-dependent lateral shift at an interface due to a spin–orbit interaction. When circularly polarized light is incident on a particle at the surface, it typically generates an optical lateral force (OLF) of the order of ∼0.05 pN/(mW·μm^–2) governed by PSHE [Nature Photonics 9, 809 (2015)]. Intuitively, the net OLF vanishes when two beams of equal intensity with opposite circular polarizations (e.g., left- and right-handed) are incident simultaneously. In this work, we exploited the phase-engineered PSHE by superposing two chiral beams with opposite circular polarizations and a controlled phase difference. Both theoretical analysis and experimental results demonstrate that this approach, combining engineered phase difference with circular polarization control, significantly enhances the OLF up to the order of ∼1.0 pN/(mW·μm^–2). This large optical lateral force (LOLF) enables new applications in PSHE-based systems and optical micromanipulation.