Mapping Optical Lateral Forces on the Poincaré Sphere

Abstract

Optical lateral forces (OLFs) play progressively important roles in optical manipulation, finding numerous applications in enantioselective sorting and sensing. Probing OLFs on achiral particles is also essential in interpreting extraordinary light–matter interactions. Recent advances have shown that the OLF can emerge from the transverse Belinfante spin momentum (BSM) and get maximum values when the light is circularly polarized. Here, by searching the Poincaré sphere, we find that the optical gradient force and radiation pressure correlate strongly with the ellipticity and azimuthal angles on the Poincaré sphere, which may exceed the OLF in a focused line-shaped beam. Consequently, the total lateral force may reach its maximum under the elliptical polarization rather than the circular polarization. Meanwhile, the ellipticity angle corresponding to the maximum force varies significantly with the particle size and its refractive index. Our work unravels a novel and efficient way to harness optical forces in a full-polarization manner and provides a new playground for various biophysical applications.