Improving the emission efficiency of periodic plasmonic structures for lasing applications

We report on a two dimensional plasmonic structure that utilizes an Ag film for the generation of surface plasmons and a layer of the organic semiconductor tri(8-hydroxyquinoline) aluminum (Alq₃) doped with the laser dye 4-dicyanmethylene-2-methyl-6-(p-dimethylaminostyryl)-4 H-pyran (DCM) as an active medium. The dispersion diagram of this structure exhibits a plasmonic bandgap in the dye emission wavelength range. At the flat band-edge, the group velocity tends to zero, so that the density of surface plasmon modes is high. This may yield a lasing action. However, the device suffers from the energy dissipation due to metal absorption and unwanted radiation. We examine how some of them may be overcome. Firstly, we propose the use of long range surface plasmons (LRSPs) characterized by a low loss coefficient. To this end, we investigate theoretically and experimentally the best conditions for the excitation of these modes. A strong emission is observed compared to that from a planar structure. These modes provide a high performance-an enhancement factor of 3-when the dye thickness is about 100 nm, a value consistent with the numerical findings. We further demonstrate that the use of a spacer layer significantly increases the emission efficiency. Finally, we suggest a specific design for the laser structure for minimal radiation loss.     

Radiation characteristics of multilayer periodic dielectric structures

Radiation characteristics of multilayer periodic dielectric structures are investigated by the method which combines the building block approach of multimode network theory with the rigorous mode matching procedure. The multilayer periodic structure is composed of uniform dielectric layers and single periodic layers. Two examples are given in this paper; first, radiation property of the double dielectric grating antenna is analyzed. The results indicate that the double dielectric grating antenna has relatively smaller dimensions than that of the single one. It is undoubtly of great importance in the case that the limitation of the weight and the volume of the system is strictly required. Secondly, some curved profile grating antennas are analyzed by combining the present method with the staircase approximation. In such a way, the effects of groove profile on the performance of the grating antennas are systemetically studied and some useful guidelines for the design of the dielectric grating antennas are thereby suggested.     

Exciton transfer between localized states in ZnO quantum well structures

The dynamics of photocreated excitons in a CdZnO/MgZnO quantum well (QW) was studied by comparing the experimental photoluminescence (PL) data with the results of Monte Carlo simulations of the exciton hopping. The temperature-dependent PL linewidth was found to be in reasonable agreement with the model of exciton hopping, with an additional inhomogeneous broadening (Γ) accounted for. The simulation analysis revealed fluctuations of the band potential to be 20 meV with an additional inhomogeneous broadening of , and a crossover from a non-thermalized to thermalized exciton energy distribution at about 100 K. In addition, a Bose–Einstein distribution like temperature dependence of the exciton energy in the wells was extracted using the data on the PL peak position.     

Partially coherent bidirectional reflectance distribution data computation for modeling periodic plasmonic structures at infrared wavelengths

A series of methods for employing Rigorous Coupled Wave Analysis (RCWA) to predict bidirectional reflectance distributions for periodic plasmonic surface structures, under partial longitudinal spatial coherence conditions, is presented. Two new methods are presented, which accurately represent the effects of directionally dependent absorption on the profiles of reflected diffraction lobes. Bidirectional reflectance distribution functions may be fit to the resulting bidirectional reflectance distributions, allowing plasmonic structures to be accurately incorporated into infrared scene-rendering and component modeling tools.     

On the use of a hierarchical multi-level building block basis function scheme in periodic plasmonic structures

A Volumetric Method of Moments algorithm is applied to predict the plasmonic responses of chiral metamaterials. This algorithm is based on the use of a multi-level building block basis function scheme, in combination with a dedicated Kummer transformation in the calculation of periodic Green’s functions. The validity of the algorithm is demonstrated by analyzing a Ninja Star periodic structure. A good agreement can be found between simulation and experiment.     

Controlling magnetic dipole transition with magnetic plasmonic structures

A plasmonic structure with double gold patches is proposed for enhancing the spontaneous emission of a magnetic dipole transition through a magnetic hot area. A Purcell factor of nearly 2000 can be obtained at optical frequencies together with a low sensitivity in spatial and spectral mismatches between the light emitter and the resonance mode. The associated resonance can be tuned from the visible to the IR frequencies, enabling efficient control of forbidden transitions using plasmonic structures.     

Resonance interaction of optical phonons with localized states

The optical-phonon Green’s function averaged over the positions of defects—both point and line— is calculated with allowance for possible localized states near the boundary of the continuous spectrum and for their intrinsic damping. The frequency-transfer dependence of the cross section for Raman scattering is calculated with the aid of this Green’s function.     

Current-voltage characteristics of SIS structures with localized states in the material of the barrier layer

Elastic resonant tunneling through a single localized state in an insulating layer (I-layer) situated in the constriction zone between two thick superconducting electrodes is investigated theoretically, and the current-voltage characteristic (IVC) of the structure is calculated. The accompanying analysis leads to the prediction that an appreciable current can flow through the structure, not at |eV|=2Δ (Δ is the modulus of the order parameter of the superconducting electrodes) as in the case of an ordinary SIS junction, but at |eV|⩾Δ, and also that the IVC can acquire segments of negative differential resistance in the case of tunneling through a single localized state. Averaging of the IVC over an ensemble of localized states distributed uniformly throughout the volume of the I-layer and with respect to the energy near the chemical potential min the limit Γ₀/Δ≫1 (Γ₀ is the half-width of the resonance line of the localized state) produces a smaller excess current than in a junction of the SNS type. It is shown that the IVC’s exhibit a transition from an excess current to a deficit current as Γ₀ decreases in the high-voltage range. Zh. éksp. Teor. Fiz. 114, 687–699 (August 1998)     

Convective instability of a water-vapor-saturated atmospheric layer. The formation of localized and periodic cloud structures

The classical Rayleigh problem of convective instability is generalized to the case of water vapor condensation in the atmosphere. We present an analytical solution demonstrating a fundamental difference between moist convection and Rayleigh convection: the curve of the critical Rayleigh number versus the number characterizing the intensity of condensation heat release consists of two parts, with spatially localized neutral solutions corresponding to one of them. Spatially periodic neutral solutions correspond to the second part of the curve; these are characterized by a significant localization of the regions of ascending motions. The theory describes the nucleation and development of individual convective clouds and ordered cloud structures.     

含周期性空腔结构吸声机理的研究

为了研究水下含周期性空腔结构的吸声机理,建立并验证了含轴对称空腔周期性结构吸声特性计算的简化有限元仿真方法,用简化的有限元模型结合遗传算法对水下环境含周期性圆柱空腔结构的吸声性能进行了优化设计.从能量耗散、变形和模态的角度分析了含周期性空腔结构的吸声机理.空腔结构谐振包括表层的弯曲振动和空腔附近的径向变形,且径向运动也...     

Analysis of periodic thin-film structures with rectangular profiles

A rigorous analysis is presented for thin-film structures on which a rectangular-profile grating layer is superimposed. Typical dispersion curves are calculated for guided leaky waves, which are relevant to beam couplers in integrated-optics applications.     

Synthesis of periodic plasmonic microstructures with copper nanoparticles in silica glass by low-energy ion implantation

Ion implantation was used to locally modify the surface of silica glass to create periodic plasmonic microstructures with Cu nanoparticles. Nanoparticles were synthesized by Cu-ion irradiation of the silica glass at the ion energy of 40 keV, dose of 5×10¹⁶ ions/cm² and current density of 5 μA/cm². This procedure involves low-energy ion implantation into the glass through a mask placed at the surface. Formation of nanoparticles was observed by optical spectroscopy and atomic force microscopy. The presented results clearly demonstrate how the low-energy ions can be used for the fabrication of photonic microstructures on dielectric surfaces in a single-step process.     

Performance analysis of nitride alternative plasmonic materials for localized surface plasmon applications

We consider methods to define the performance metrics for different plasmonic materials to be used in localized surface plasmon applications. Optical efficiencies are shown to be better indicators of performance as compared to approximations in the quasistatic regime. The near-field intensity efficiency, which is a generalized form of the well-known scattering efficiency, is a more flexible and useful metric for local-field enhancement applications. We also examine the evolution of the field enhancement from a particle surface to the far-field regime for spherical nanoparticles with varying radii. Titanium nitride and zirconium nitride, which were recently suggested as alternative plasmonic materials in the visible and near-infrared ranges, are compared to the performance of gold. In contrast to the results from quasistatic methods, both nitride materials are very good alternatives to the usual plasmonic materials.     

Observation of the spin-based plasmonic effect in nanoscale structures

Observation of surface-plasmon phenomena that are dependent upon the handedness of the circularly polarized incident light (spin) is presented. The polarization-dependent near-field intensity distribution obtained in our experiment is attributed to the presence of a geometric phase arising from the interaction of light with an anisotropic and inhomogeneous nanoscale structure. A near-field vortex surface mode with a spin-dependent topological charge was obtained in a plasmonic microcavity. The remarkable phenomenon of polarization-sensitive focusing in a plasmonic structure was also demonstrated.     

Dispersion characteristics of spin waves in planar periodic structures based on ferromagnetic films

A technique for calculating the dispersion characteristics of planar periodic magnetic structures is suggested. It is based on joint application of the spin-wave mode analytical approach and the transfer matrix formalism. The dispersion characteristics of a planar periodic waveguiding medium representing a thin ferromagnetic film with an array of metallic strips (metallic grating) on its surface are calculated. It is shown that the dispersion characteristics of planar periodic structures based on ferromagnetic films depend, not only on the geometry of the waveguiding system, but also on the surface anisotropy of the initial film.     

超短脉冲激光诱导周期性表面结构

激光诱导周期性表面结构（Laser-induced periodic surface structures,LIPSS）具有纳米尺度的特征结构和自重复的微观尺度的排列图案,因此,LIPSS在传感器、太阳能发电、光催化等方面具有广泛的应用前景。本文首先介绍LIPSS形成过程中超快激光与物质相互作用的复杂过程,强调瞬态光学性质和表面结构变化的作用。然后综述几种具有代表性的LIPSS形成机理,并且讨论了各自的优缺点。接着介绍了LIPSS形成过程中材料的变化,主要包括材料化学成分、晶体结构和表面微观结构的变化。最后综述了LIPSS在材料表面处理、光学和机械等方面的应用。     

Enhanced acetone sensing characteristics by decorating Au nanoparticles on ZnO flower-like structures

A well-organized hierarchical structure of ZnO was developed by chemical bath deposition and used as templates for making gold-coated ZnO (Au/ZnO) hybrid nanostructures. The coverage of Au nanoparticles (Au NPs) on ZnO was controlled by changing the amount of the Au precursor. The Au/ZnO hybrids were applied as gas sensing materials to detect acetone. The improved sensor response, selectivity and short response, and recovery time to acetone vapor due to Au NPs on ZnO nanostructures has been observed and explained by considering the formation of Au/ZnO heterostructures, which are favorable for the diffusion of gas molecules. In addition, the dependence of Au amount on gas sensor properties was systematically investigated. ZnO decorated by 6 wt% Au NPs displayed a 9.05-fold enhancement in gas response to 100 ppm of acetone at 280 °C compared to pristine ZnO.     

Control and managing of localized states in two-dimensional systems with periodic forcing

We study the formation of localized structures in two-dimensional systems with periodic forcing, showing that these types of systems provide an adequate framework for the study and control of localized structures. Theoretically, we introduce a dissipative ϕ ⁴ model as a prototype for a bistable spatially forced system, and we show that with different spatial forcings of small amplitudes, such as square or hexagonal grids, this model exhibits a family of localized structures. By changing the forcing parameters, we control the bistability between the various induced patterns. Experimentally, based on an optical feedback with spatially amplitude-modulated beam, we set-up a two-dimensional forced experiment in a nematic liquid crystal cell. By changing the forcing parameters, the system exhibits a family of localized structures that are confirmed by numerical simulations for the average liquid crystal tilt angle.     

Dynamic analysis of periodic structures

The natural vibration analysis of a periodic structure with repeated identical substructures may be simplified by using some symmetrical properties of the substructure dynamic matrices, resulting in a set of linear difference equations in the displacements. These equations are readily solved for cyclic symmetric systems, simply supported systems and infinite systems. The order of the overall frequency equations is at most equal to one half of the total number of degrees of freedom retained for a single substructure regardless of the number of substructures in the system. With these natural modes, the system with general boundary conditions at end stations is analyzed by a fast converging method.     

Resonance properties of magmatic structures

The observation of quasi-harmonic spectral components in the response of volcanic structures to distant seismic events is reported. The resonance frequencies are associated with the presence of a magma center and a magma chamber that contain gas cavities or bubbles. The presence of the region with a reduced density in the vicinity of the Elbrus volcano is confirmed by independent gravimetric measurements and by the results of analyzing the geological data.