铁氧体内嵌金属线阵宽带负折射特性研究

采用具有大饱和磁化强度(MS)的铁氧体基片提供宽带负μ、内嵌金属线阵列提供负ε的方法,合成了一种X频段8.5～10.7GHz宽带负折射材料.对采用上述合成材料构成的半无限大异向介质平板的电磁波反射、透射等特性进行了研究,抽取得到该合成材料的有效介电常数、有效磁导率、折射率等系列电磁特性参数;同时对电磁波穿过采用上述合成材料构成的半无限大楔形和平面透镜发生的折射、汇聚等现象进行了研究.结果表明,合成材料的有效介电常数、有效磁导率以及折射率的实部在8.5～10.7GHz频带范围内皆为负值.在该频段上,合成材料具有"负折射效应" "双负效应""平面镜成像效应"等负折射异向介质典型的电磁特性.     

折射率浅释

折射是光入射介质的多种光学现象之一,而折射率是表征各种介质(材料)物理、化学性质的重要参数。科学界对其了解伴随着光学发展的整个历程。文章从折射率的定义出发,介绍了它的物理含义、测量方法、应用以及关于"负折射率"的研究发展。     

负折射材料实验验证的研究进展

负折射材料已成为近几年来物理学,材料科学,电子科学等交叉学科领域的研究热点。首先介绍负折射材料的基本原理,并详细介绍近年来这类材料的仿真与实验研究。     

手征超常介质结构及其强旋光性和负折射率

介绍了手征超常介质产生负折射率的基本理论,概括了目前几种常见的手征超常介质的结构模型,综述了手征超常介质结构的旋光性和圆二色性,以及手征超常介质在微波段、红外及可见光频段的负折射特性研究进展,指出了手征超常介质结构的损耗和均匀性问题.     

微波左手材料及其应用前景

左手材料是一种介电常数ε和磁导率μ同时为负的人工周期结构材料,在其中传播电磁波的群速度与相速度方向相反,从而呈现出许多奇异特性.本文介绍了左手材料的基本概念、实现原理,综述了其在理论与实验研究方面取得的最新进展、研究热点、缺陷效应及实现负折射的其它途径.最后对左手材料的应用前景进行了展望.     

左手材料设计与制备的研究进展

左手材料是一种介电常数ε和磁导率μ同时为负值的超材料,具有许多非常奇异的电磁学性质.阐述了左手材料的基本概念和性质,介绍了能够同时实现负介电常数和负磁导率的Ω形、S形和树枝等单一结构,综述了利用机械加工法和化学制备法制备的高频段负磁导率材料,以及基于耦合作用的电磁波垂直入射条件下左手材料的设计与制备方法,阐述了超材料负磁导率或左手行为的验证方法,最后展望了左手材料的应用前景.     

基于超材料的全向辐射空间功率合成研究

设计了一种由银纳米纤维周期排列成各向异性的圆环形超材料,在二维空间实现全向辐射的高效率空间功率合成。研究发现在太赫兹频率下该各向异性超材料径向介电常数趋于零。通过数值仿真观察TM极化的电磁波磁场强度经过圆环形径向各向异性零折射超常介质时磁场空间分布。计算表明,无论激励源位置如何和激励源数量多少,TM极化的电磁波磁场强度在经过此超常介质后,总能实现电磁波全向辐射。不同激励源合成的磁场强度通过此径向零折射超常介质能产生空间相干的全向辐射,最终实现全向辐射的空间功率合成。     

双曲超材料及其传感器研究进展

超材料为具有超常电磁性质的人工结构,因拥有自然界材料没有的介电常数、磁导率和折射率等电磁性质而引起人们的关注。双曲超材料是具有强各向异性介电张量或磁导率张量的介质,其介电常数张量或磁导率张量的分量在一个或两个空间方向上为负,与其他类型的超材料相比,双曲超材料具有在光学频率下相对容易制造、宽带非共振和三维体响应以及灵活的波长可调谐性等优点。本文综述了双曲超材料的特性、实现方法、可调谐及活性以及其作为超灵敏传感器的发展,重点讨论了基于金属/介质多层结构及金属纳米线阵列的双曲超材料作为生物传感器的原理及研究进展,并指出双曲超材料传感器发展的长期目标是结构简单、便于制备、宽频带和多元分析。     

光学材料的进展

光学材料是指具有一定的光学性质和功能的材料,应用于光学仪器和光学实验。光学材料包括有机和无机物质,以无机物为主,也分晶态和非晶态物质。传统的光学材料是指光介质材料,是传输光线的材料,以折射、反射和透射方式改变光线的方向、强度和位相,使按     

带缺陷零折射率超常材料的声透射

0引言近年来,声波在超常材料中的传播特性受到了广泛关注。声超常材料作为一种新型人工复合材料其等效声学参数分布可以人为设定从而实现对声波的任意调控。超常材料包含正参数材料[1]、负参数材料[2-3]以及零参数材料[4-7]。各向异性的正参数材料可实现物体的声隐身[1],负参数材料可实现负折射和完美透镜等[3]。除了正、负参数超常材料,研究人员最近也证明了零参数及近零参数声超常材料的存在并将其应用于波阵面调制及弯曲波导等[4-7]。     

Reflection and refraction properties of plane waves on the interface of uniaxially anisotropic chiral media

We have investigated the reflection and refraction properties of plane waves incident from free space into a uniaxially anisotropic chiral medium, where the chirality appears only in one direction and the host medium can be either an isotropic dielectric or an anisotropic electric plasma. We show that the reflection and refraction properties are closely related to the dispersion relation of the chiral medium and that negative phase refractions and/or negative group refractions may occur. We further demonstrate that the two eigenwaves within the uniaxially anisotropic chiral medium behave differently with respect to the incident angle, and in some cases only one of them can be supported and transmitted. We have studied the critical angle and Brewster's angle with some special properties. We have also discussed the potential application of the uniaxially anisotropic chiral medium for the polarization beam splitter. Numerical results are given to validate our analysis.     

Optical negative refraction by four-wave mixing in thin metallic nanostructures

The law of refraction first derived by Snellius and later introduced as the Huygens-Fermat principle, states that the incidence and refracted angles of a light wave at the interface of two different materials are related to the ratio of the refractive indices in each medium. Whereas all natural materials have a positive refractive index and therefore exhibit refraction in the positive direction, artificially engineered negative index metamaterials have been shown capable of bending light waves negatively. Such a negative refractive index is the key to achieving a perfect lens that is capable of imaging well below the diffraction limit. However, negative index metamaterials are typically lossy, narrow band, and require complicated fabrication processes. Recently, an alternative approach to obtain negative refraction from a very thin nonlinear film has been proposed and experimentally demonstrated in the microwave region. However, such approaches use phase conjugation, which makes optical implementations difficult. Here, we report a simple but different scheme to demonstrate experimentally nonlinear negative refraction at optical frequencies using four-wave mixing in nanostructured metal films. The refractive index can be designed at will by simply tuning the wavelengths of the interacting waves, which could have potential impact on many important applications, such as superlens imaging.     

Negatively refracting atomic vapour

A new mechanism for realizing negative refractive index with a four-level atomic system is suggested. The explicit expressions for the electric permittivity and magnetic permeability at probe frequency are presented. It is shown that there is a frequency band in which the four-level photonic-resonant atomic vapour may exhibit simultaneously negative permittivity and permeability, and that such an atomic vapour may become a left-handed material (negatively refracting medium). Compared with the previous schemes to realize negative refraction within the framework of classical electromagnetic theory, the most remarkable features of the present scenario are as follows: (i) isotropic material with microscopic structure units at atomic-scale level, (ii) negative refraction in visible and infrared frequency bands, (iii) controllable manipulation by external fields and (iv) based on quantum coherence in a multilevel atomic system.     

A study of light collection efficiency in scintillation detectors

A group of computer programs was set up to study the light of collection efficiency in scintillation detectors with rectangular cross sections. The input conditions can be chosen arbitrarily, including: the size, light attenuation length and refraction index of the scintillator and light guide, the refraction index of the coupling medium, the reflection characteristics of the walls, and the position of light sources. A few examples are discussed in this article.     

An ‘electromagnetic wiggler’ originating from refraction of waves at the side edge of a Bragg reflector

Calculations are reported which predict that light incident on the side edge of a Bragg reflector can show varied and unusual refraction behaviour, including a rapid transition from positive to negative refraction. Although under certain conditions negative refraction can occur, it is concluded that perfect lensing based on it is unlikely to be realised in practice. However, it is shown that light incident obliquely on the structure can be made to propagate normal to the interface after refraction while exhibiting lateral oscillations of its Poynting vector, an effect that could possibly find application in an ‘electromagnetic wiggler’. It is also shown that negative group velocity rather than negative effective mass is required for the observation of the negative refraction, and in the case of low refractive index contrast, negative refraction occurs only when the size of the illumination spot exceeds a critical value, which is inversely proportional to the contrast of the refractive indices.     

Focusing properties of a photonic crystal slab with multiple mechanisms in addition to negative refraction

A brief review of imaging by a photonic crystal (PC) slab with negative refraction is given. The focusing properties of the PC with multiple mechanisms in addition to negative refraction are studied by the finite-difference time-domain method. In addition to the effect of negative refraction, there are multiple mechanisms that are all attributed to the PC focusing properties, including Bragg diffraction, excitation of the surface mode, and self-collimation. The resulting field pattern is the total result of these factors. Bragg diffraction occurs in the high-frequency domain and mainly influences the quality of focusing in the optical axis direction. The excitation of the surface mode improves the resolution of focusing. Self-collimation makes the focusing position deviate from Snell's law.     

Microwave focusing and beam collimation using negative index of refraction lenses

Negative index of refraction materials (NIMs) were first postulated by Veselago in 1968 and have recently been realised using structures formed with rings and wires deposited on printed circuit boards. The proof of the existence of negative index of refraction was established using a Snell's law experiment with a wedge. The predicted and measured refraction angles were found to be consistent for a negative index material and in excellent agreement with the theoretical expectations. For microwave lenses NIMs have the advantage of being lighter, having better focusing properties and potentially lower aberrations. Simulation and experimental results on NIM configurations including gradient index of refraction and spherical 3D lenses are presented. Both focusing and beam collimating applications will be considered. These results will be compared to normal positive index of refraction material lenses     

Quantum-interference and the concentration of Er3+ ion effect on left-handedness with zero absorption and large negative refractive index in Er3+:YAG crystal

The electromagnetically induced left-handedness with zero absorption and large negative refractive index was investigated in a solid Er³⁺:YAG crystal with a four-level system proposed for an atomic medium. It was found that the frequency region with simultaneous negative permittivity and negative permeability, the zero absorption intervals, and the maximum values of the negative refractive index can be adjusted by changing the signal field, the coherent field, as well as the concentration of Er³⁺ ion in crystal. It is shown that wider zero absorption intervals with a higher index of refraction can be easily obtained when the signal field is only off resonance. The slab fabricated by the left-handed solid medium Er³⁺:YAG crystal with zero absorption may be a practical candidate for designing perfect lenses.     

S波由饱和土入射于弹性土时在界面上的反射与透射

从地震工程实际出发，借助Biot多孔介质中的波动方程，根据各种界面条件导出了S波从饱和土入射于弹性土时在交界面上反射与透射的一般计算公式。作为算例，数值计算分析了S波从饱和土入射于饱和土与弹性土交界面时，饱和土中P1、P2和S波的反射系数以及弹性土中P波、SV射系数与界面排水条件、入射角以及频率之间的关系。结果表明：各种波的反射、透射系数与入射角、入射频率以及界面排水条件有关系。     

Flow Birefringence Studies: Scattering of a light wave by a turbulent flow showing optical anisotropy

The Mueller matrix of a scattering volume is calculated in two cases. In the first case, the medium is subjected to thermal fluctuations and the index of refraction is a random function. In the second case, the medium is a turbulent boundary layer showing flow birefringence. For both cases, the turbulence is considered as a random homogeneous isotropic process and the spectrum correlation functions of the index of the refraction are assumed to be gaussian. The results are compared in the case of a wave scattered perpendicular to the wave direction.