Optical force control of electromagnetic response particles induced by three-dimensional electromagnetic fields

The selective enhancement or suppression of optically induced electric and magnetic forces in dielectric nanoparticles through dynamic field tuning remains a significant challenge. Herein, we demonstrate a phase-based approach that enables continuous and quantitative modulation of the balance between electric and magnetic optical forces on germanium (Ge) nanospheres through phase-dependent three-dimensional (3D) electromagnetic fields. Specifically, by varying the initial phase from 0 to 0.5<i>π</i> of the tightly focused generalized cylindrical vector beams (CVBs), the peak magnetic-to-electric longitudinal force ratio can be enhanced by 260% (i.e., from 0.5 to 1.8). This tunability originates from the asymmetric nature of dipole forces: the magnetic dipole force is predominantly conservative, while the electric dipole force contains a non-conservative curl component that is highly sensitive to phase-induced field vorticity. The underlying mechanism, involving continuous switching between electric-dominant and magnetic-dominant regimes, is further validated by the correlated evolution of scattering cross-sections and longitudinal field intensities. These results establish phase-modulated 3D fields as a versatile platform for tailoring magneto-electric optical forces, offering new opportunities in optical trapping, nanoparticle sorting, and nanoscale assembly.