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Register a new userSurface plasmon polariton assisted optical pulling force
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We demonstrate both analytically and numerically the existence of optical pulling forces acting on particles located near plasmonic interfaces. Two main factors contribute to the appearance of this negative reaction force. The interference between the incident and reflected waves induces a rotating dipole with an asymmetric scattering pattern while the directional excitation of surface plasmon polaritons (SPP) enhances the linear momentum of scattered light. The strongly asymmetric SPP excitation is determined by spin-orbit coupling of the rotating dipole and surface plasmon polariton. As a result of the total momentum conservation, the force acting on the particle points in a direction opposite to the incident wave propagation. We derive analytical expressions for the force acting on a dipolar particles placed in the proximity of plasmonic surfaces. Analytical expressions for this pulling force are derived within the dipole approximation and are in excellent agreement with results of electromagnetic numerical calculations. The forces acting on larger particles are analyzed numerically, beyond the dipole approximation.
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The tremendous progress in light scattering engineering made it feasible to develop optical tweezers allowing capture, hold, and controllable displacement of submicronsize particles and biological structures. However, the momentum conservation law imposes a fundamental restriction on the optical pressure to be repulsive in paraxial fields. Although different approaches to get around this restriction have been proposed, they are rather sophisticated and rely on either wavefront engineering or utilize active media. Herein, we revisit the issue of optical forces by their analytic continuation to the complex frequency plane and considering their behavior in transient. We show that the exponential excitation at the complex frequency offers an intriguing ability to achieve a pulling force for a passive resonator of any shape and composition even in the paraxial approximation, the remarkable effect which is not reduced to the Fourier transform. The approach is linked to the virtual gain effect when an appropriate transient decay of the excitation signal makes it weaker than the outgoing signal that carries away greater energy and momentum flux density. The approach is implemented for the Fabry-Perot cavity and a high refractive index dielectric nanoparticle, a fruitful platform for intracellular spectroscopy and lab-on-a-chip technologies where the proposed technique may found unprecedented capabilities.
Recently, guiding electromagnetic surface waves without sacrificing scattering losses through paths that have arbitrary shape bumps has gained a lot of interest due to its wealth of advantages in modern photonics and plasmonics devices. In this study, based on transformation optics (TO) methodology, a feasible approach to control the flow of surface plasmon plariton (SPPs) at metal-dielectric interfaces with arbitrary curvature is proposed. The obtained material becomes homogeneous and independent of the bumps geometry. That is, one constant material is required to route SPP waves without scattering the energy into the far-field region, which overcome the bottlenecks encountered in the previous works. Several numerical simulations are carried out to illustrate the capability of the propounded cloak to control the SPP flows at metal/dielectric interfaces. The unique designing approach introduced here may open a new horizon to nano-optics and downscaling of photonic circuits.
We consider the electromagnetic field near an interface between two media with arbitrary real frequency-dependent permittivities and permeabilities, under conditions supporting the surface plasmon-polariton (SPP) propagation. The dispersion of the electric and magnetic properties is taken into account based on the recent approach for description of the spin and momentum of electromagnetic field in complex media [Phys. Rev. Lett. 119, 073901 (2017); New J. Phys., 19, 123014 (2017)]. It involves the Minkowski momentum decomposition into the spin and orbital parts with the dispersion-modified permittivities and permeabilities. Explicit expressions are derived for spatial densities of the energy, energy flow, spin and orbital momenta and angular momenta of the transverse-magnetic (TM) SPP field. They are free from non-physical singularities; the only singular contribution describes a strictly localized surface part of the spin momentum that can be associated with the magnetization current in the conductive part of the SPP-supporting structure. On this ground, a phenomenological theory of the SPP-induced magnetization (predicted earlier based on the simplified microscopic approach) is outlined. Possible modifications and generalizations, including the transverse-electric (TE) SPP waves, are discussed.
We experimentally demonstrate the use of subwavelength optical nanoantennae to assist the gentle ablation of nanostructures directly using ultralow fluence from a Ti: sapphire oscillator through the excitation of surface plasmon waves. We show that this ablation mechanism is the same for metal and dielectric. The analytical solutions of ablation threshold are in excellent agreement with the experiment estimations. Surface plasmon assisted locally enhanced ablation at nanoscale provides a method for nanomachining, manipulation and modification the nanostructures without collateral thermal damage to the materials. It is also shown that this ablation can deposit low-density high quality thin nano film.
This paper proposes a new method to achieve robust optical pulling of particles by using an air waveguide sandwiched between two chiral hyperbolic metamaterials. The pulling force is induced by mode conversion between a pair of one-way-transport surface-arc waves supported on the two metamaterial surfaces of the waveguide. The surface arcs bridge the momentum gaps between isolated bulk equifrequency surfaces (EFSs) and are topologically protected by the nontrivial Chern numbers of the EFSs. When an incident surface-arc wave with a relatively small wavenumber $k_{x1}$ is scattered by the particle, a part of its energy is transferred to the other surface-arc mode with $k_{x2}(>k_{x1}). Because the electromagnetic wave acquires an additional forward momentum from the particle proportional to $k_{x2}-k_{x1}$ during this process, the particle will always be subjected to an optical pulling force irrespective of its material, shape and size. Since the chiral surface-arc waves are immune to backscattering from local disorders and the metamaterials are isotropic in the xy plane, robust optical pulling can be achieved in a curved air waveguide and can go beyond standard optical pulling mechanisms which are limited to pull in a straight-line.
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