Fano-enhanced pulling and pushing optical force on active plasmonic nanoparticles

Abstract

We demonstrate tunable pulling and pushing optical forces on plasmonic nanostructures around Fano resonance. The plasmonic nanostructure containing a spherical core with optical gain and a metallic shell shows much larger optical pulling force than a pure gain sphere. One can obtain large field enhancement and giant pulling force at the emerged quadrupole mode. The introduction of optical pump compensate the dissipative loss from metal shell, thus enable the strong coupling between a narrow quadrupole mode and a board dipole mode, giving rise to Fano resonance. The giant negative forces origin from the reversal of electric field at Fano resonance, which lead to pulling force on bound currents and charges. Meanwhile, the separation of the Lorentz force helps to reveal the nature of the pulling forces in gain system. We have shown that by applying the Lorentz force density formula, it is possible to obtain the correct value of the force inside our complex inhomogenous structure made up of dispersive and lossy metamaterial irrespective of the electromagnetic momentum density. Our results provide a practical way to manipulate nanoparticles and give deep insight into light-matter interaction.

Optomechanical Processing of Silver Colloids: New Generation of Nanoparticle–Polymer Composites with Bactericidal Effect

“…The induced dipole is then drawn by field intensity gradients, which compete with radiation pressure due to momentum transferred from the photons in the beam. In free space, radiation pressure is proportional to the Poynting vector, which determines the direction and magnitude of the momentum flow [ 24 , 25 ]. Physically, the Poynting vector expresses the law of conservation of light momentum after its interaction with particles on which scattering occurs.…”

Ballistic supercavitating nanoparticles driven by single Gaussian beam optical pushing and pulling forces

“…Optical forces on an object due to the exchange of photon momentum with the object [17][18][19][20][21][22][23][24][25][26][27] can move nanoswimmers/ microswimmers along the beam direction. Light propulsion has unique advantages like wireless control, high spatial and temporal precision, and instant response 28 .…”

“…However, the achieved moving speed is only~0.5 body-length s −1 , and the same strategy may not be applicable to objects in homogenous media, which are the cases for most nanoswimmers/microswimmers. Theoretically, an object in homogenous medium can also be pulled by a single planewave if the object has certain unique optical configurations to enable either optical gain 25,26 or near-field electromagnetic coupling between dielectric-metallic NP dimers 27 . However, the experimental demonstration in homogenous media is still lacking.…”

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“…The gradient force arises from the evanescent interaction between localized optical modes, resulting in a direct force enhancement under optical resonant conditions, indeed representing the basis of most optical tweezer set-up. [28] The gradient force can be increased by orders of magnitude by employing different kinds of exotic photonic materials such as metamaterials, [27] photonic crystals, [30] evanescently www.afm-journal.de www.advancedsciencenews.com coupled waveguides, [31] or plasmonic nanostructures [32] as they all act directly on the enhancement of the local field. In particular, the strength of the gradient optical force between two interacting metallic nanoparticles can be greatly enhanced by resonantly exciting the nanoparticles with sub-100 nm interparticle separation.…”