电磁诱导下Y型四能级原子系统的左手效应

采用了一个闭合的Y型四能级原子系统,在多模光场的作用下,利用量子相干技术使其实现介质的左手效应,使介质具备左手材料特性. 在相互作用表象下,考虑偶极近似和旋转波近似,利用密度矩阵方程并结合相关条件下的有关公式进行理论计算. 数值模拟结果显示：在合适的参量条件下,介质的相对介电常量和相对磁导率可以同时出现负值,产生了左手效应,相应的介质转化为左手材料.在弱探测场条件下,当探测光的拉比频率增加时,介质实现左手效应的频率范围减小并且与之相对应的折射率和吸收系数也发生变化. 通过讨论在左手效应成立的条件下介质对光场的吸收和增益问题,结果表明：在弱探测场条件下,利用电磁诱导的方法也可以实现介质的左手效应,使得左手材料在实验上的实现也得到了进一步的扩展,同时也扩展了电磁诱导的应用领域.     

Simultaneous negative permittivity and permeability in a coherent atomic vapour

A new quantum optical mechanism to realize simultaneously negative electric permittivity and magnetic permeability is suggested. In order to obtain a negative permeability, we choose a proper atomic configuration that can dramatically enhance the contribution of the magnetic-dipole allowed transition via the atomic phase coherence. It is shown that the atomic system chosen with proper optical parameters can give rise to striking electromagnetic responses (leading to a negative refractive index) and that the atomic vapour becomes a left-handed medium in an optical frequency band. Differing from the previous schemes of artificial composite metamaterials (based on classical electromagnetic theory) to achieve the left-handed materials, which consist of anisotropic millimetre-scale composite structure units, the left-handed atomic vapour presented here is isotropic and homogeneous at the atomic-scale level. Such an advantage may be valuable in realizing the superlens (and hence perfect image) with left-handed atomic vapour.     

The coexistence of TE-TM surface waves in uniaxially anisotropic left-handed materials

We investigate theoretically the characteristics of surface waves in uniaxially anisotropic left-handed materials. The constraints for the existence of TE and TM polarized surface waves in uniaxially anisotropic left-handed materials are identified. We discuss mainly whether TE and TM polarized surface modes may coexist in the same frequency domain at the interface between one isotropic regular medium and another uniaxially anisotropic left-handed medium. It is shown that the answer to the coexistence of TE and TM surface modes is really positive. The Poynting vector and the density of energy associated with surface modes are calculated. Depending on the system parameters either TE or TM surface modes has the time averaged Poynting vector directed opposite or same to the mode phase velocity. In the presence of anisotropy, negative refraction does not need to be left-handed. We show that the characteristics of surface waves in uniaxially anisotropic left-handed media are significantly different from that in isotropic left-handed media.     

Numerical simulations of negative-index refraction in a lamellar composite with alternating single negative layers

Negative-index refraction is demonstrated in a lamellar composite with epsilon-negative (ENG) and mu-negative (MNG) materials stacked alternatively. Based on the effective medium approximation, simultaneously negative effective permittivity and permeability of such a lamellar composite are obtained theoretically and further proven by full-wave simulations. Consequently, the renowned left-handed metamaterial comprising split ring resonators and wires is interpreted as an analogy of such ENG--MNG layers. In addition, beyond the effective medium approximation, the propagating field squeezed near the ENG/MNG interface is demonstrated to be left-handed surface waves with backward phase velocity.     

Optical Magnus effect in metamaterials fabricated from ferromagnetic microwires

In homogeneous negative phase velocity media, the Doppler and Cherenkov-Vavilov effects and the refraction and pressure of light are anomalous: they are inverse with respect to the corresponding effects in conventional media. Using the geometrical optics approximation, it is shown that the optical Magnus effect in inhomogeneous negative phase velocity media is also anomalous. The effect is demonstrated by considering a metamaterial consisting of parallel amorphous ferromagnetic microwires in a magnetic field. The metamaterial proves to be a left-handed one in the realistic region of the electromagnetic spectrum. The optical properties of such a left-handed medium can be controlled by the external magnetic field.     

Negative refraction and left-handed electromagnetism in microwave photonic crystals

We demonstrate the negative refraction of microwaves in a metallic photonic crystal prism. The spectral response of the photonic crystal prism, which manifests both positive and negative refraction, is in complete agreement with band-structure calculations and numerical simulations. The validity of Snell's law with a negative refractive index is confirmed experimentally and theoretically. The negative refraction observed corresponds to left-handed electromagnetism that arises due to the dispersion characteristics of waves in a periodic medium. This mechanism for negative refraction is different from that in metamaterials.     

Photonic-resonant left-handed medium

A new scheme to realize simultaneously negative permittivity and permeability in a coherent atomic vapor medium (photonic-resonant material) via a coherent driving mechanism is suggested. It is verified that the atomic system coherently driven by a strong optical field will give rise to a negative refractive index in certain probe frequency ranges. One of the most remarkable features of the present scheme is such that a slab fabricated by the left-handed vapor medium is an ideal candidate for designing perfect lenses since the photonic-resonant atomic vapor cannot only exhibit an isotropic negative refractive index, but also provide a good impedance match at the air-medium interfaces.     

Radiation reflection from an optical inhomogeneity moving in a right- and left-handed medium

The parametric Doppler effect in a medium whose dielectric permittivity and magnetic permeability become negative in some spectral range is analyzed with respect to uniform plane waves. The regime in which the medium is right-handed (the refractive index is positive) for incident radiation and left-handed (the refractive index is negative) for reflected wave is demonstrated. The possibility of the occurrence of additional branches in the dispersion dependences is demonstrated.     

Study of the field emitted by a source placed inside a two-dimensional left-handed metamaterial

We studied the properties of electromagnetic waves that were emitted from a source placed inside a left-handed medium based on a two-dimensional labyrinth. While the arguments of geometrical optics suggest that the field emitted from the source would be focused outside the left-handed medium no matter where the source was placed, our results proved the contrary. We found that the field emitted from the source was focused outside the left-handed medium when the source was placed inside the medium at a certain distance away from the interface. Moreover, our results showed that the field emitted from the source was focused on the subwavelength dimensions outside the left-handed medium.     

双负媒质结构改善Ku波段天线辐射特性

基于负介电常数和负磁导率产生原理,采用金属细线和裂环谐振器结构,针对12.5 GHz频率开展双负媒质结构设计。通过特殊边界条件下S参数计算以及Nicolson-Ross-Weir方法,完成等效参数的提取,获得介电常数、磁导率、折射率实部均为负值,且折射率接近于0的左手材料特性。将双负媒质结构加载于Ku波段圆锥喇叭口面进行仿真优化,提高天线增益2.17 dB,在11~13 GHz频带范围内,加载天线的增益均有所改善。实验结果表明,口面加载双负媒质结构后,天线增益提高1.51 dB,后向辐射减小5.7 dB,辐射特性获得了明显改善。     

Excitation of surface and volume electromagnetic waves in left-handed media by an electron bunch

We study theoretically the Vavilov-Čerenkov radiation from a nonrelativistic electron bunch moving in free space over a left-handed medium. It is shown that in the frequency range in which the refractive index of the medium is negative, Vavilov-Čerenkov radiation leads to simultaneous excitation of volume and surface electromagnetic waves in the same frequency range. The wave vector of the surface wave in the plane of an interface of two media is greater in magnitude than the corresponding quantity for the volume wave. The energy fluxes of volume and surface waves in the left-handed medium are studied. The radiation pattern of the bunch is found. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 5, pp. 406–417, May 2007.     

双负媒质结构改善Ku波段天线辐射特性

基于负介电常数和负磁导率产生原理,采用金属细线和裂环谐振器结构,针对12.5 GHz频率开展双负媒质结构设计。通过特殊边界条件下S参数计算以及Nicolson-Ross-Weir方法,完成等效参数的提取,获得介电常数、磁导率、折射率实部均为负值,且折射率接近于0的左手材料特性。将双负媒质结构加载于Ku波段圆锥喇叭口面进行仿真优化,提高天线增益2.17 dB,在11~13 GHz频带范围内,加载天线的增益均有所改善。实验结果表明,口面加载双负媒质结构后,天线增益提高1.51 dB,后向辐射减小5.7 dB,辐射特性获得了明显改善。     

Negative refraction and rough surfaces: A new regime for lensing

The action of a rough, but differentiable, interface upon the passage of rays between air and a left-handed medium is considered. It is shown that negative refraction brings rays to a focus at distances closer to the boundary than can be attained by conventional refraction. This effect enables a new mechanism for reflection to occur, even in media that are impedance matched, caused principally by rays undergoing two interactions with the interface via paths that pass exclusively through air or the left-handed medium.     

Resonant tunneling of a wave through a structure that contains a layer with a negative refractive index

We have investigated the transmission ability of a layered structure the central layer of which is made of a “left-handed” material (its refractive index is negative) and is separated by two air slabs from a “right-handed” dielectric medium that surrounds the structure. We consider tunneling of energy fluxes through the structure and determine conditions for the complete (reflectionless) transmission of the power of the incident wave through it. We show that this effect is resonant and is observed when the tangential component of the wave vector of the incident wave coincides with the longitudinal wave vector of one of waveguiding eigenmodes of the left-handed layer.     

Blue light emission and amplification in left-handed isotropic Metallo-Semiconductor Photonic Crystal

A new left-handed isotropic design of semiconductor Photonic Crystal with plasmonic (Aluminum) nanorod inclusion is analyzed and proposed to demonstrate All-Angle Negative Refraction (AANR) with blue light amplification. It is shown that the proposed structure provides negative real values of both permeability (μ) and permittivity (?) with extremely low imaginary values for visible light. Phase slope and phase velocity is shown to be negative for blue light for proposed left-handed structure. Index matched to the incident medium and compensated losses due the gain assistance lead the light amplification in the designed structure. Finite Difference Time Domain (FDTD) method is applied to study left-handed transmission and reflection properties. Extremely high Left-Handed Transmission Efficiency is calculated which is found to be more than 99% for the proposed structure. Fabrication tolerance with effect of change in plasmonic nanorod radius by ±10% is also analyzed. Further, left-handed transmission for blue light is confirmed by analyzing the far-field spectrums of the proposed structure obtained by employing 3D FDTD method. Demonstration and study of near-field and far-field resonance reveals the nano-photonic application potential of the proposed structure as directional optical nano-antenna, polarizer and filter.     

谐振频率可调的环状开口谐振器结构及其效应

理论和实验研究表明，开口谐振环(SRRs)中可以激励磁谐振从而实现负磁导率.通过在SRRs结构中引入与其开口边平行的金属短杆设计并制备了新的磁谐振单元，采用波导法系统研究了短杆对SRRs和左手材料的微波透射特性以及左手效应的影响.实验和数值模拟表明：金属短杆和SRRs开口边形成附加电容，导致SRRs开口电容增大从而引起谐振频率降低.随短杆长度l和短杆与SRRs间距d的增大，SRRs谐振频率也随之减小和增加.短杆的加入不影响SRRs的负磁导率特性，改变短杆与SRRs间距d< 关键词： 开口谐振环 金属短杆 调控 左手材料     

Left-handed chiral metamaterials

In this work, the concept of left-handed chiral metamaterials is analyzed by emphasizing their optical ability on the rotation of the plane of polarization of a wave. The possibilities of a negative phase velocity, negative and positive propagation constants, and basic electromagnetic properties of this novel medium are also presented. After the characterization of left-handed chiral metamaterial, we provide a reflection and transmission study for two planar boundaries of nonchiral-left-handed chiral metamaterial for normal angles of incidence. Some numerical results are also provided to validate the formulation found in the analysis and to show the role of the chirality in the propagation constants, phase velocities, reflection and transmission.      

Characterization and electromagnetic response of a ?-shaped metamaterial

In this paper we experimentally and numerically study the left-handed behavior in a biplanar metamaterial operating at microwave frequency. The metamaterial consists of ϕ-shaped metallic patterns on both sides of a dielectric spacer. The origin of negative refractive index is elucidated by performing the effective medium analysis. Additionally, the dependence of the left-handed transmission on geometric parameters, such as the periodicities, the shapes of metallic slabs and continuous wires, and the impact of spacer separation, is examined.     

Negative permeability in a <Emphasis Type="Bold">Λ</Emphasis>-type three-level atomic vapor

A new approach is suggested to realize negative magnetic permeability that follows directly from quantum mechanics. It is shown that a Λ-type three-level atomic system with proper atomic parameters can give rise to striking magnetic responses, which could exhibit negative permeability in an optical frequency band. Both steady and transient behaviors of the magnetic permeability in the atomic vapor are studied. The present negative-permeability vapor could be mixed with a quantum coherent vapor whose electric permittivity is negative. Such a mixed vapor may give an isotropic left-handed vapor medium at the atomic-scale level. PACS 32.10.Dk; 42.50.Gy; 78.20.Ci     

Is there an experimental verification of a negative index of refraction yet?

We show that recent claims of experimental verification of a negative index of refraction in metallic metamaterials, "left-handed" microwave frequencies, are questionable. At these frequencies the imaginary part of the dielectric permittivity is significant or even dominates its real part, and hence the effective medium behaves as a metal, i.e., with losses below the cutoff frequency of relevance. Then, the refractive index is complex, and there is not a distinction between right- and left-handed material because the electromagnetic wave is inhomogeneous. Just by using this idea we explain the transmittivities that were recently obtained in experiments by Shelby et al. [Science 292, 77 (2001) and Appl. Phys. Lett. 78, 489 (2001)].