Internal optical forces in plasmonic nanostructures

Abstract

We present a computational study of the internal optical forces arising in plasmonic gap antennas, dolmen structures and split rings. We find that very strong internal forces perpendicular to the propagation direction appear in these systems. These internal forces show a rich behaviour with varying wavelength, incident polarisation and geometrical parameters, which we explain in terms of the polarisation charges induced on the structures. Various interesting and anomalous features arise such as lateral force reversal, optical pulling force, and circular polarisation-induced forces and torques along directions symmetry-forbidden for orthogonal linear polarisations. Understanding these effects and mastering internal forces in plasmonic nanostructures will be instrumental in implementing new functionalities in these nanophotonic systems.

Plasmonic Spherical Heterodimers: Reversal of Optical Binding Force Based on the Forced Breaking of Symmetry

“…Though Lorentz force analysis has been applied previously in [29][30][31][32] to understand the mechanism of chirality induced force, Luneburg lenses, mechanical interaction between light and graded index media, cloaking effect, background effect on radiation pressure; such analysis is rare to understand the plasmonic effects and plasmonic binding force. Although it is commonly believed that plasmonic forces mostly arise from the surface force/polarization induced charges [33,34], our study suggests a notably different proposal especially for the off-axis heterodimers.…”

“…In Fig. 5 (d) and (h) we have plotted the difference of the bulk Lorentz force, which clearly suggests that the total binding force is dominated by the bulk part of Lorentz force [which is in contrast with the commonly observed dominance of surface [33]/polarization charge induced force [34] for plasmonic objects]. This force can be considered as the scattering force part [33,54] of the total force, which is physically originating from the multiple scattering between the smaller and the bigger object.…”

“…Another important fact is that: though Lorentz force analysis has been applied previously in 29 – 33 to understand several different purposes; such a fundamental analysis is rare to understand the plasmonic effects and plasmonic binding force. It is commonly believed that plasmonic forces mostly arise from the surface force/polarization induced charges 34 , 35 . But our study based on Lorentz force suggests a notably different proposal especially for the off-axis (near end fire) heterodimers.…”

Substrate and Fano Resonance Effects on the Reversal of Optical Binding Force between Plasmonic Cube Dimers

“…Our ultimate conclusion is that: (i) the reversal starts to occur from strong multiple scattering and (ii) though it is commonly believed that internal wave-field does not contribute much for optical force on plasmonic objects (cf. the dominance of surface force in refs 35 , 36 ), during the Fano resonance the scenario is quite different.…”

Design Considerations of Gold Nanoantenna Dimers for Plasmomechanical Transduction

“…The Maxwell stress tensor method was used for calculation of the optical forces on the gold dimers. This method has been implemented multiple times for its reliability for calculation of optical forces in plasmonic nanostructures [15,16]. In contrast to the conventional approach of enclosing a box over the nanoparticle's surface and calculating the forces on it, the force tensor components were integrated di-rectly over the gold nanodisc surface.…”