Cascaded plasmonic nanorod antenna for large broadband local electric field enhancement

We propose a cascaded plasmonic nanorod antenna for large broadband electric near-field enhancement. The structure has one big gold nanorod on each side of a small two-wire antenna which consists of two small gold nanorods. For each small nanorod, the enhanced and broadened optical response can be obtained due to the efficient energy transfer from its adjacent big nanorod through strong plasmonic near-field coupling. Thus, the electric field intensity of the cascaded antenna is significantly larger and broader than that of the individual small two-wire antenna. The resonant position, field intensity enhancement, and spectral width of the cascaded antenna are highly tunable by varying the geometry of the system. The quantum efficiency of the cascaded antenna is also greatly enhanced compared with that of the small antenna. Our results are important for the applications in field-enhanced spectroscopy.     

Light transmission and local field enhancement in arrays of silver nanocylinders

Vertical silver nanocylinders have been fabricated by two-photon microfabrication technique. The three-dimensional propagation of visible light along and between the nanocylinders has been characterized by wide-field transmission microscopy. Transmission spectra were collected with a fiber coupled spectrometer and optical images were taken with a camera using an inverted microscope. Intensity enhancements occur along the nanocylinders surfaces for wavelengths in the visible range. Finite-difference time domain (FDTD) simulations are in good agreement with the experimental results. The electromagnetic field enhancement was evaluated, in order to analyze the suitability of the studied structures for sensing applications.     

Refractive index dependent local electric field enhancement in cylindrical gold nanohole

We report on the local electric field characters in a long cylindrical gold nanohole. Theoretical calculation results based on quasi-static model show that the local environmental dielectric constant dependent electric field intensity and field distribution in the gold nanohole show quite unique properties, different from those in the thin gold nanotube. Because of the thick gold wall, no plasmon hybridization exists. So there is only one resonance frequency taking place, and the intense local field has been focused into the gold nanohole. Our main finding is that, the local field in the nanohole is largely dependent on the inner hole refractive index and outer environmental refractive index. The competition between inner hole and outer polarization leads to a non-monotonic change of the local field intensity with increasing the dielectric constant of the nanohole. This refractive index controlled local field enhancement in cylindrical gold nanohole presents a potential for tunable surface-enhanced fluorescence and novel nano-optical biosensing applications.     

Application of plasmonic silver films in histology for contrast enhancement

We have studied the absorption spectra and micrographs of sections of cells of the epithelium and andenocarcinoma of the large intestine, immobilized between standard glass slides and cover glasses and plasmonic silver films. We have shown that when we use a microtome technique and specially selected plasmonic silver films, we can achieve enhancement of the image contrast in analysis of the cell morphology as a result of the increase in the light absorption and scattering cross sections with the contrasting stains hematoxylin and eosin.     

Cascaded optical field enhancement in composite plasmonic nanostructures

We present composite plasmonic nanostructures designed to achieve cascaded enhancement of electromagnetic fields at optical frequencies. Our structures were made with the help of electron-beam lithography and comprise a set of metallic nanodisks placed one above another. The optical properties of reproducible arrays of these structures were studied by using scanning confocal Raman spectroscopy. We show that our composite nanostructures robustly demonstrate dramatic enhancement of the Raman signals when compared to those measured from constituent elements.     

Spatial dependence of the local field enhancement in dielectric shell coated silver nanospheres

The dependence of the local field factor around dielectric shell coated silver nanospheres was investigated by theoretical calculation as a function of the spatial distance. The local field factors in the dielectric shell are sensitive to the distance from particle center and shell thickness. When the shell dielectric constant is greater than that of surrounding medium, the maximum of local field factor at inner surface of the shell red shift and increases nonlinearly with increasing the shell thickness. On the contrary, when shell dielectric constant is less than that of surrounding medium, increasing the shell thickness leads the maximum of local field factor at inner surface blue shifts and decreases nonlinearly. However, with increasing the shell thickness, the maximum of local field factor at exterior surface of the shell always decrease nonlinearly. Furthermore, with increasing shell thickness, all these variations get gentle approach to a constant value when the shell thickness is two times of the core radius. When the core and shell diameter have fixed values, the local field factors in dielectric shell decrease with increasing the distance from particle center, but the peak position is not sensitive to the distance.     

Chiral plasmonic nanostructure of twistedly stacked nanogaps

Nanogap plasmonic structures with strong coupling between separated components have different responses to orthogonal-polarized light, giving rise to giant optical chirality. Here, we proposed a three-dimensional(3D) nanostructure that consists of two vertically and twistedly aligned nanogaps, showing the hybridized charge distribution within 3D structures.It is discovered that the structure twisted by 60° exhibits plasmonic coupling behavior with/without gap modes for different circular-polarized plane waves, showing giant chiral response of 60% at the wavelength of 1550 nm. By controlling the disk radius and the insulator layer, the circular dichroism signal can be further tuned between 1538 and 1626 nm.     

Effects of the local environment on plasmonic coupling of metallic nanotube arrays

We have theoretically investigated the effect of the dielectric core and the dielectric embedding medium separately on the transmission spectra and plasmonic properties of coupled metallic nanotube arrays.It is found that the plasmonic properties of the nanotube arrays are strongly influenced by the presence of the dielectric which induces additional screening charges.We show that instead of one single photonic bandgap for the hollow nanotube arrays placed in air,an additional photonic bandgap arises from t...     

Smart inverters with broadband light absorption enhancement of nanostructure plasmonic solar absorber using PSO algorithms and FDTD method

Optical Review - Solar plasmonics absorbers have received outstanding interest from nanotechnology. However, they have small efficiency. To overcome this challenge, we have used two ways in this...     

Electric field enhancement between two parallel cylinders due to plasmonic resonance

We theoretically examine the electric field enhancement in the narrow gap between two parallel cylinders due to the plasmonic resonance. The resonance condition and the field enhancement factor are found explicitly. It is shown that the resonance occurs at frequencies lower than the plasma frequency. This effect results from the special geometry: the gap width between parallel cylinders is much smaller than their radii. It is also shown that the enhancement coefficient is much larger than the one for a single cylinder and is determined together with the resonance frequency by the system geometry.     

Hyperthermal chaotic photodesorption of xenon from alumina-supported silver nanoparticles: plasmonic coupling and plasmon-induced desorption

Excitation of Xe monolayers on alumina-supported silver nanoparticles (AgNPs) by laser light in the (1,0) Mie plasmon resonance can lead to desorption of Xe atoms with hyperthermal energy and chaotic time structure. The chaotic behavior is most likely due to plasmonic coupling between AgNPs. We argue that the desorption is induced by direct energy transfer to the adsorbate from the Pauli repulsion of the collectively oscillating electrons of the plasmon at the surface. A simple model calculation shows that this is possible. A connection between both effects appears likely.     

Biconical-taper-assisted fiber interferometer with modes coupling enhancement for high-sensitive curvature measurement

A modal interferometer based on multimode–singlemode–multimode fiber structure built with a biconical taper for fiber curvature measurement is proposed and experimentally demonstrated. Due to the tapered singlemode fiber acting as a high-efficient mode power converter to enhance the modes coupling, curvature sensor with improved sensitivity is achieved by monitoring the defined fringe visibility of the interference spectrum. The measuring range can be tuned by changing the waist diameter of the fiber taper. Meanwhile, the sensor shows an intrinsic ability to overcome the influence of temperature cross-sensitivity and the power fluctuation of light source. The advantages of easy fabrication, high-quality spectrum with improved sensitivity, and small hysteresis will provide great potential for practical applications of the sensor.     

Ricci curvature non-minimal derivative coupling cosmology with field re-scaling

In this letter, cosmology of a simple NMDC gravity with \(\xi R \phi _{,\mu }\phi ^{,\mu }\) term and a free kinetic term is considered in flat geometry and in presence of dust matter. A logarithm field transformation \(\phi ' = \mu \ln \phi \) is proposed phenomenologically. Assuming slow-roll approximation, equation of motion, scalar field solution and potential are derived as function of kinematic variables. The field solution and potential are found straightforwardly for power-law, de-Sitter and super-acceleration expansions. Slow-roll parameters and slow-roll condition are found to depend on more than one variable. At large field the re-scaling effect can enhance the acceleration. For slow-rolling field, the negative coupling \(\xi \) could enhance the effect of acceleration.     

Local field enhancement of pair arrays of silver nanospheres

Local field surface plasmon excitation of pair arrays of silver nanospheres was studied using three-dimensional finite-difference time-domain method. The near-field enhancement was associated with the radius of nanosphere and the incident wavelength, the highest of which always appeared in the penultimate gaps, regardless of the number of the pairs. The surface plasmon resonance could be controlled and tuned by radius of nanosphere and incident wavelength.     

Quantum theory for plasmon-assisted local field enhancement

We applied quantum theory for nonlocal response and plasmon-assisted field enhancement near a small metallic nanoscale antenna in the limit of weak incoming fields. A simple asymmetric bio-inspired design of the nanoantenna for polarization-resolved measurement is proposed. The spatial field intensity distribution was calculated for different field frequencies and polarizations. We have shown that the proposed design the antenna allows us to resolve the polarization of incoming photons.     

Tunable coupling of a hybrid plasmonic waveguide consisting of two identical dielectric cylinders and a silver film

The propagation length of surface plasmon polaritons(SPPs) is intrinsically limited by the metallic ohmic loss that is enhanced by the strongly confined electromagnetic field. In this paper, we propose a new class of hybrid plasmonic waveguides(HPWs) that can support long-range SPP propagation while keeping subwavelength optical field confinement. It is shown that the coupling between the waveguides can be well tuned by simply varying the structural parameters. Compared with conventional HPWs, a larger propagation length as well as a better optical field confinement can be simultaneously realized. The proposed structure with better optical performance can be useful for future photonic device design and optical integration research.     

十字形银纳米结构的表面等离子体光子学性质

本文应用离散偶极子近似方法计算了十字形银纳米结构的消光光谱及其近场电场强度分布. 研究表明相比于单根纳米棒, 十字形纳米结构能够提供更强的表面电场; 由于相邻凸起间的电场耦合作用, 当入射光的偏振方向改变时, 在十字形纳米结构的侧表面总能激发出较强的电场.另外, 本文还系统地研究了十字形纳米结构的形貌参数对其表面等离子体共振峰的影响. 这些结果将会指导十字形纳米结构的制备, 以满足其在表面增强拉曼散射中的应用.     

Tunable Fano resonances and plasmonic hybridization of gold triangle–rod dimer nanostructure

A gold dimer structure consisting of a notched triangle nanoslice and a rectangle nanorod is proposed to produce distinct Fano resonance. Owing to the coupling between the dipole plasmon mode of the nanorod and the dipole or quadrupole plasmon mode of the nanoslice, the extinction spectrum with a deep Fano dip is formed and can be well fitted by the Fano interference model for different geometry parameters. In addition, Fano resonance of the gold dimer nanostructure also intensely depends on the polarization direction of incident light. Moreover, Fano resonance of the triangle–rod trimer is also analyzed by adding another nanorod into the former dimer and exhibits the splitting of plasmonic resonant peak in high order coupling modes. The plasmonic hybridizations in these nanostructures have been analyzed for revealing the physical origin of the Fano resonance.     

Near-field second-harmonic generation induced by local field enhancement

The field near a sharp metal tip can be strongly enhanced if irradiated with an optical field polarized along the tip axis. We demonstrate that the enhanced field gives rise to local second-harmonic (SH) generation at the tip surface thereby creating a highly confined photon source. A theoretical model for the excitation and emission of SH radiation at the tip is developed and it is found that this source can be represented by a single on-axis oscillating dipole. The model is experimentally verified by imaging the spatial field distribution of strongly focused laser modes.