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This paper investigates theoretically and numerically local heating effects in plasmon nanofocusing structures with a particular focus on the sharp free-standing metal wedges. The developed model separates plasmon propagation in the wedge from the resultant heating effects. Therefore, this model is only applicable where the temperature increments in a nanofocusing structure are sufficiently small not to result in significant variations of the metal permittivity in the wedge. The problem is reduced to a one-dimensional heating model with a distributed heat source resulting from plasmon dissipation in the metal wedge. A simple heat conduction equation governing the local heating effects in a nanofocusing structure is derived and solved numerically for plasmonic pulses of different lengths and reasonable energies. Both the possibility of achieving substantial local temperature increments in the wedge (with a significant self-influence of the heating plasmonic pulses), and the possibility of relatively weak heating (to ensure the validity of the previously developed nanofocusing theory) are demonstrated and discussed, including the future applications of the obtained results. Applicability conditions for the developed model are also derived and discussed. [ABSTRACT FROM AUTHOR]

We develop a computationally efficient method for the theoretical analysis of thermophoresis of nanoparticles and adatoms on crystalline surfaces (thermal tweezers) for efficient parallel nanofabrication. The analysis of surface diffusion of particles or adatoms in the presence of strong temperature gradients is conducted through the direct determination of probability distributions for diffusing particles, using the numerical solution of the Smoluchowski diffusion equation with varying (temperature-dependent) diffusion constant. The local values of the diffusion constant are determined from the Fokker–Planck equation for the considered crystalline potential of the substrate and local temperature. Steady-state and nonsteady-state particle distributions on the surface are obtained and analyzed in the presence of optically-induced strong temperature gradients. Detailed comparison of this approach with the previously obtained results from the Monte Carlo simulations of the Langevin equation is conducted, demonstrating high computational efficiency, and accuracy of the new method in the high-friction regime. Applicability conditions for the developed method are also determined and discussed. [ABSTRACT FROM AUTHOR]

In this paper, we investigate theoretically and numerically the efficiency of energy coupling from a plasmon generated by a grating coupler at one of the interfaces of a metal wedge into the plasmonic eigenmode (i.e., symmetric or quasisymmetric plasmon) experiencing nanofocusing in the wedge. Thus the energy efficiency of energy coupling into metallic nanofocusing structure is analyzed. Two different nanofocusing structures with the metal wedge surrounded by a uniform dielectric (symmetric structure) and with the metal wedge enclosed between a substrate and a cladding with different dielectric permittivities (asymmetric structure) are considered by means of the geometrical optics (adiabatic) approximation. It is demonstrated that the efficiency of the energy coupling from the plasmon generated by the grating into the symmetric or quasisymmetric plasmon experiencing nanofocusing may vary between ∼50% to ∼100%. In particular, even a very small difference (of ∼1%-2%) between the permittivities of the substrate and the cladding may result in a significant increase in the efficiency of the energy coupling (from ∼50% up to ∼100%) into the plasmon experiencing nanofocusing. Distinct beat patterns produced by the interference of the symmetric (quasisymmetric) and antisymmetric (quasiantisymmetric) plasmons are predicted and analyzed with significant oscillations of the magnetic and electric field amplitudes at both the metal wedge interfaces. Physical interpretations of the predicted effects are based upon the behavior, dispersion, and dissipation of the symmetric (quasisymmetric) and antisymmetric (quasiantisymmetric) film plasmons in the nanofocusing metal wedge. The obtained results will be important for optimizing metallic nanofocusing structures and minimizing coupling and dissipative losses. [ABSTRACT FROM AUTHOR]

We conduct the detailed numerical investigation of a nanomanipulation and nanofabrication technique—thermal tweezers with dynamic evolution of surface temperature, caused by absorption of interfering laser pulses in a thin metal film or any other absorbing surface. This technique uses random Brownian forces in the presence of strong temperature modulation (surface thermophoresis) for effective manipulation of particles/adatoms with nanoscale resolution. Substantial redistribution of particles on the surface is shown to occur with the typical size of the obtained pattern elements of ∼100 nm, which is significantly smaller than the wavelength of the incident pulses used (532 nm). It is also demonstrated that thermal tweezers based on surface thermophoresis of particles/adatoms are much more effective in achieving permanent high maximum-to-minimum concentration ratios than bulk thermophoresis, which is explained by the interaction of diffusing particles with the periodic lattice potential on the surface. Typically required pulse regimes including pulse lengths and energies are also determined. The approach is applicable for reproducing any holographically achievable surface patterns, and can thus be used for engineering properties of surfaces including nanopatterning and design of surface metamaterials. [ABSTRACT FROM AUTHOR]

Using rigorous numerical methods of analysis, this paper investigates nonadiabatic nanofocusing in tapered nanorods with the major emphasis on structural optimization for achieving maximal possible local field enhancement. Simple analytical equations for the determination of the optimal length of the tapered rod are presented and discussed. It is also shown that for the considered structures, optimal taper angle and optimal length of the rod only very weakly depend on the radius of curvature of the rounded tip of the rod. Contrary to this, enhancement of the local electric field at the rounded tip strongly increases with decreasing radius of the tip. Comparison of the numerical results with the adiabatic theory of nanofocusing results in accurate verification of the applicability conditions for adiabatic approximation in tapered nanorods. [ABSTRACT FROM AUTHOR]

We investigated the effect of dielectric filling in a V groove on the propagation parameters of channel plasmon-polariton (CPP) modes. In particular, existence conditions and critical groove angles, mode localization, field structure, dispersion, and propagation distances of CPP modes are analyzed as functions of dielectric permittivity inside the groove. It is demonstrated that increasing dielectric permittivity in the groove results in a rapid increase of mode localization near the tip of the groove and increase of both the critical angles that determine a range of groove angles for which CPP modes can exist. Detailed analysis of the field structure has demonstrated that the maximum of the field in a CPP mode is typically reached at a small distance from the tip of the groove. The effect of rounded tip is also investigated. [ABSTRACT FROM AUTHOR]

We demonstrate that efficient adiabatic nanofocusing of plasmons can be achieved using a sharp metal wedge (thin tapered film) on a dielectric substrate. It is shown that the quasisymmetric (with respect to the charge distribution across the wedge) plasmon mode can experience infinite adiabatic slowing down with both its phase and group velocities reducing to zero as the plasmon propagates towards the tip of the wedge. Conditions for strong local field enhancement near the tip are determined and analyzed. In particular, it is demonstrated that the electric field in the plasmon experiences much stronger local enhancement than the magnetic field. Two distinct asymptotic regimes with the electric field amplitude approaching either zero or infinity at the tip of the wedge (tapered film) are described. The results are compared to adiabatic nanofocusing of plasmons by metallic V grooves and sharp metal wedges in a uniform dielectric. [ABSTRACT FROM AUTHOR]

Several studies are conducted to explain the efficiency of the plasmon energy coupling taking place in the nanofocusing metal wedges. The efficiency of the coupling is shown to be highly dependent on the changes taking place in the permittivities of the substrate.

Numerous studies are conducted to explain the different shape effects occurring in the tapered metal rods with adiabatic nanofocusing of the strongly localized surface plasmons. The tapered rods with convex shape are shown to be more beneficial and advantageous, as compared to those with concave shapes.

Nanofocusing of electromagnetic radiation, that is, reducing the cross sections of propagating optical modes far beyond the diffraction limit in dielectric media, can be achieved in tapered metal-dielectric waveguides that support surface plasmon-polariton modes. Although the main principles of nanofocusing were formulated over a decade ago, a deep theoretical understanding and conclusive experimental verification were achieved only a few years ago. These advances have spawned a variety of new important technological possibilities for the efficient delivery, control and manipulation of optical radiation on the nanoscale. Here, we present the underlying physical principles of radiation nanofocusing in metallic nanostructures, overview recent progress and major developments, and consider future directions and potential applications of this subfield of nano-optics. [ABSTRACT FROM AUTHOR]

The extremely asymmetrical scattering (EAS) of bulk and guided electromagnetic waves in nonuniform periodic Bragg arrays with steplike variations of the grating amplitude is analyzed theoretically by means of a recently developed approach based on allowance for the diffractional divergence of the scattered wave. Arrays of finite and infinite widths are investigated. It is shown that, for thin nonuniform arrays, EAS has the same pattern as for uniform arrays with mean grating amplitude. On the contrary, for wide nonuniform arrays, the scattered wave amplitudes are well determined by local values of the grating amplitude. In this case, the energy of the scattered wave is shown to concentrate mainly in regions with smaller grating amplitude. The sensitivity of EAS to small imperfections of periodic arrays is investigated theoretically. The physical explanation of the observed effects is based on the diffractional divergence of the scattered wave.

We propose and investigate theoretically and experimentally L-shaped gap surface plasmon waveguides (L-GSPWs) formed by a dielectric film (strip) partially enclosed between two metal films. The proposed L-GSPWs combine the benefits of strong plasmon localization in a nanogap, significant propagation distance, low cross-talk between two neighboring waveguides, high transmission through a sharp 90° bend, and simplicity of fabrication by means of the standard lithography combined with the thin film deposition., (© 2011 American Chemical Society)

In this paper, we present a comprehensive numerical study of the wavelength-dependence of transmission through sharp 90 degrees bends in metallic slot waveguides with sub-wavelength localization and varying geometrical parameters. In particular, it is demonstrated that increasing the plasmon wavelength results in a significant increase (up to nearly 100%) of transmission through the bend, combined with a reduction in the mode asymmetry in the second arm of the bend. The mode asymmetry and its relaxation are explained by interference of the transmitted mode with non-propagating and leaky modes generated at the bend. Comparison with the two-dimensional case of a metal-dielectric-metal waveguide is also conducted, showing significant differences for the slot waveguides based on the presence of different non-propagating and leaky modes.