金属纳米颗粒双圆环阵列的表面格点共振效应

由金属纳米粒子构成的周期性规则阵列,可以通过粒子间的耦合来激发表面格点共振效应,从而极大压缩单粒子的局域表面等离子体共振效应的线宽.本文将该表面格点共振效应从二维周期性结构推广到轴对称的圆环结构中,提出了双圆环金属纳米粒子阵列结构的电磁响应模型.在此基础上,得到了双圆环阵列发生表面格点共振效应的条件,并发现当阵列结构参数满足特定条件时,该阵列的所有偶极子分量会发生集体共振效应,从而获得极高的近场增强因子.     

零势场中变质量粒子的束缚能谱

结合点正则变换(PCT)与分析转移矩阵(ATM)两种方法,得到了零势场中变质量粒子的束缚能谱.通过计算变质量粒子穿透零势场的概率,发现并解释了透射谱中共振峰与本征能量的一一对应关系.     

Pseudopotential multi-relaxation-time lattice Boltzmann model for cavitation bubble collapse with high density ratio

The dynamics of the cavitation bubble collapse is a fundamental issue for the bubble collapse application and prevention. In the present work, the modified forcing scheme for the pseudopotential multi-relaxation-time lattice Boltzmann model developed by Li Q et al. [ Li Q, Luo K H and Li X J 2013 Phys. Rev. E 87 053301] is adopted to develop a cavitation bubble collapse model. In the respects of coexistence curves and Laplace law verification, the improved pseudopotential multi-relaxation-time lattice Boltzmann model is investigated. It is found that the thermodynamic consistency and surface tension are independent of kinematic viscosity. By homogeneous and heterogeneous cavitation simulation, the ability of the present model to describe the cavitation bubble development as well as the cavitation inception is verified. The bubble collapse between two parallel walls is simulated. The dynamic process of a collapsing bubble is consistent with the results from experiments and simulations by other numerical methods. It is demonstrated that the present pseudopotential multirelaxation-time lattice Boltzmann model is applicable and efficient, and the lattice Boltzmann method is an alternative tool for collapsing bubble modeling.     

基于改进伪势LBM的空泡溃灭建模

为研究空化泡溃灭阶段的数值仿真,本文以格子Boltzmann方法为基础,采用改进作用力引进格式,对改变力学稳定性条件相关参数进行优化。通过最优参数提取,提高该多相格子Boltzmann模型密度比,从而最大程度保证热力学一致性及模型稳定性。并通过共存密度曲线对比及误差值计算,确定了参数的最优值。基于改进伪势格子Boltzmann模型对空泡溃灭进行建模,并将计算结果和实验结果对比,验证了空泡溃灭模型的有效性,对实际运用有一定的指导意义。     

Polarization and structure dependent optical characteristics of the three-arm nanoantenna with C_(3v) symmetry and broken symmetry

The optical properties of a three-arm plasmonic nanoantenna with and without broken symmetry were analyzed in detail. For the symmetrical structure, the local electric field can be significantly enhanced and well confined within the feed gap, whilst the extinction spectrum illustrates polarization independence. With broken symmetry, multi-wavelength resonances are observed due to the single dipole resonance and dipole–dipole coupling effect, and wide tunability is also available through minor structural adjustment. Especially when illuminated by a circularly polarized light beam, the extinction and the electric field distribution can be effectively modulated by just varying the incident wavelength.     

Angular-modulated spatial distribution of ultrahigh-order modes assisted by random scattering

In designing an optical waveguide with metallic films on a nanometer scale, the random scattering by the natural roughness of the thin film is always ignored. In this paper, we demonstrate that for the ultrahigh-order modes (UOMs) in the symmetric metal cladding waveguide, such a scattering leads to drastic variations in their spatial distribution at different incident angles. Owing to the high mode density of the UOMs, the random scattering induced coupling can be easily related to different modes with different propagation directions or wavenumbers. At small incident angles, the intra-mode coupling dominates, which results in a spatial distribution in the form of concentric rings. At large incident angles, the inter-mode coupling plays the most important role and leads to an array-like pattern. Experimental evidence via optically trapped nanoparticles support the theoretical hypothesis.     

Quantum reflection as the reflection of subwaves

This paper studies quantum reflection with recent research on reflection coefficient. Based on the analytical transfer matrix method, a novel explanation for this phenomenon is proposed that quantum reflection is the reflection of subwaves, which originate inherently from the inhomogeneity of the fields and is always neglected in the semiclassical regime. Comparison with exact formula and the numerical calculations for different potentials has confirmed the reliability and the validity of the proposed theory.     

All-optical modulator based on a ferrofluid core metal cladding waveguide chip

We propose a novel optical intensity modulator based on the combination of a symmetrical metal cladding optical waveguide （SMCW） and ferrofluid, where the ferrofluid is sealed in the waveguide to act as a guiding layer. The light matter interaction in the ferrofluid film leads to the formation of a regular nanoparticle pattern, which changes the phase match condition of the ultrahigh order modes in return. When two lasers are incident on the same spot of the waveguide chip, experiments illustrate all-optical modulation of one laser beam by adjusting the intensity of the other laser. A possible theoretical explanation may be due to the optical trapping and Soret effect since the phenomenon is considerable only when the control laser is effectively coupled into the waveguide.     

Effect of porous surface layer on wave propagation in elastic cylinder immersed in fluid

To study the damage to an elastic cylinder immersed in fluid, a model of an elastic cylinder wrapped with a porous medium immersed in fluid is designed. This structure can both identify the properties of guided waves in a more practical model and address the relationship between the cylinder damage degree and the surface and surrounding medium. The principal motivation is to perform a detailed quantitative analysis of the longitudinal mode and flexural mode in an elastic cylinder wrapped with a porous medium immersed in fluid. The frequency equations for the propagation of waves are derived each for a pervious surface and an impervious surface by employing Biot theory. The influences of the various parameters of the porous medium wrapping layer on the phase velocity and attenuation are discussed. The results show that the influences of porosity on the dispersion curves of guided waves are much more significant than those of thickness, whereas the phase velocity is independent of the static permeability. There is an apparent "mode switching" between the two low-order modes. The characteristics of attenuation are in good agreement with the results from the dispersion curves. This work can support future studies for optimizing the theory on detecting the damage to cylinder or pipeline.     

Low-threshold bistable reflection assisted by oscillating wave interaction with Kerr nonlinear medium

Owing to the enormously enhanced oscillating wave, a minute variation of the incident light intensity will give rise to a change in the dielectric constant of the Kerr nonlinear medium and lead to a bistable reflection with an ultra-low threshold intensity, which is closely related to the angle of incidence and the thickness of the Kerr nonlinear medium. The criterion for the existence of optical bistability is derived. Our bistability scheme is simple and not limited to the TM-polarization.