Optical pulling and pushing forces exerted on silicon nanospheres with strong coherent interaction between electric and magnetic resonances

Abstract

We investigated theoretically and numerically the optical pulling and pushing forces acting on silicon (Si) nanospheres (NSs) with strong coherent interaction between electric and magnetic resonances. We examined the optical pulling and pushing forces exerted on Si NSs by two interfering waves and revealed the underlying physical mechanism from the viewpoint of electric- and magnetic-dipole manipulation. As compared with a polystyrene (PS) NS, it was found that the optical pulling force for a Si NS with the same size is enlarged by nearly two orders of magnitude. In addition to the optical pulling force appearing at the long-wavelength side of the magnetic dipole resonance, very large optical pushing force is observed at the magnetic quadrupole resonance. The correlation between the optical pulling/pushing force and the directional scattering characterized by the ratio of the forward to backward scattering was revealed. More interestingly, it was found that the high-order electric and magnetic resonances in large Si NSs play an important role in producing optical pulling force which can be generated by not only s-polarized wave but also p-polarized one. Our finding indicates that the strong coherent interaction between the electric and magnetic resonances existing in nanoparticles with large refractive indices can be exploited to manipulate the optical force acting on them and the correlation between the optical force and the directional scattering can be used as guidance. The engineering and manipulation of optical forces will find potential applications in the trapping, transport and sorting of nanoparticles.

Theory of optical forces on small particles by multiple plane waves

“…In particular, optical pulling force on an isotropic particle can be obtained through the interference of multiple plane waves, solenoidal beams 16 , or Bessel beams 17 . Furthermore, employing chiral particles, gain media, or plasmonic interfaces can also allow achieving exerted lateral and pulling forces on the particle 15,[18][19][20][21][22][23][24][25][26] .…”

Resonant binding of dielectric particles to metal surface without plasmonics

“…3 demonstrate considerable enhancement of optical force up to hundreds of pico Newtons that exceed the gravitational forces by four orders for micron size silicon particles. Expectedly, such an enormous enhancement of resonant forces is the result of extremely large Q-factors of the resonances as was considered in papers [ 16,27]. However Fig.…”

Multipole Engineering of Attractive−Repulsive and Bending Optical Forces

“…[ 54,55 ] For example, coherent interaction between the electric and magnetic responses of silicon particles was shown to provide either pulling or pushing forces, depending on system parameters. [ 56 ] Sorting of silicon particles with laser beams was shown in the study by Shilkin et al [ 57 ] Core−shell geometries allow designing multipole resonances within a structure. [ 58 ]…”