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Abstract

The effects of resonant mode interference on optical forces acting on gold core-silicon shell nanoparticles are theoretically investigated with the multipolar expansion method based on the Mie scattering theory. It is found that the total optical radiation force and its two components, the incident force and the recoil force, can be tuned flexibly by engineering the interference interaction among electric, magnetic, and anapole modes. The recoil force acting on the core-shell nanoparticles can be enhanced up to 17 pN compared with the pure silicon nanoparticles with the same size as that of the core-shell nanoparticles when the magnetic dipole resonant mode totally interferes with the electric dipole resonant mode. In addition, the incident force can also be improved to 25 pN by suppressing the interference between the electric dipole and the magnetic dipole resonances. More importantly, the maximum optical radiation force is not dominated by the strongest resonant scattering mode of the hybrid nanostructure due to the modes’ interference induced giant negative recoil forces. We hope our results not only improve the optical trapping and manipulation of core-shell nanoparticles but also help to understand the underlying physical mechanism regarding the tunable optical radiation forces induced by the tunable interference among different resonant modes in core-shell nanoparticles.

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Figures (7)

Fig. 1 Schematic showing the Au core-Si shell nanoparticles excited with a linearly polarized plane EM wave. The linearly polarized plane wave illuminates on the Au core-Si shell nanoparticles along with x direction and the polarization direction is along with z direction, as shown in the inset.

Fig. 2 Evolution of the total scattering efficiency spectra (the first column) and the contributions of ED mode (the second column), MD mode (the third column), EQ mode (the fourth column), and MQ mode (the fifth column) to the total scattering efficiency with the increase of the radii of the core for the Au core-Si shell nanoparticle (the upper panel), the Si nanoparticle (the middle panel) and the Au nanoparticle (the lower panel).

Fig. 4 Total radiation forces Ftotal (the first column), incident forces Fel (the second column) and Fml (the third column), and the recoil forces Felml (the fourth column), Felel+1 (the fifth column), and Fmlml+1 (the sixth column) as a function of the wavelength and the radii of the core for the Au core-Si shell nanoparticle (the upper panel), the Si nanoparticle (the middle panel) and the Au nanoparticle (the lower panel).

Fig. 7 Far-field scattering pattern for Type I (a), Type II (b), Type III (c), and Type IV (d) in E plane and H plane. All far-field scattering intensities are normalized with the maximum far-field scattering intensity of Type II. The incident direction of the beam is the same as the inset in Fig. 1.