利用互补天线原理求解孔缝的共振性能

利用互补天线原理从理论上推导了真空、介质窄缝的共振频率公式,在理想窄缝长度小于5倍波长、辐射角度偏离垂直方向小于30°的情况下,孔缝的共振频率点仍然可以用半波振子的辐射情况来解释,共振点满足孔缝长度等于入射波的半个波长;介质窄缝等效为半个孔缝深度的微带贴片天线,不同介电常数介质填充时的共振频率理论公式推导值和数值模拟值基本一致,相对误差在5%以内。进一步分析了窄缝阵列的耦合性能,结果表明互补天线原理可以很好地应用于分析和求解孔缝的共振性能。     

利用互补天线原理求解孔缝的共振性能

 利用互补天线原理从理论上推导了真空、介质窄缝的共振频率公式,在理想窄缝长度小于5倍波长、辐射角度偏离垂直方向小于30°的情况下,孔缝的共振频率点仍然可以用半波振子的辐射情况来解释,共振点满足孔缝长度等于入射波的半个波长;介质窄缝等效为半个孔缝深度的微带贴片天线,不同介电常数介质填充时的共振频率理论公式推导值和数值模拟值基本一致,相对误差在5%以内。进一步分析了窄缝阵列的耦合性能,结果表明互补天线原理可以很好地应用于分析和求解孔缝的共振性能。     

Receiving Antenna in a Magnetoplasma in the Resonance Frequency Band

We find the rms voltage on a receiving dipole antenna in the electromagnetic field of a quasipotential-wave packet in a magnetoplasma in the resonance frequency band. It is shown that this voltage can be determined as a product of the electromagnetic-field amplitude of the incident wave by the effective length L_eff of the receiving antenna. For a short dipole whose length is much smaller than the electromagnetic-mode wavelength, the antenna effective length is proportional to the product of the dipole effective length in free space by the excitation coefficient of quasielectrostatic waves (non-normalized electric-field pattern of a dipole). In the case where the receiving antenna is located in proximity to the resonance cone on the lighted side, this excitation coefficient is much greater than unity. Therefore, the determined voltage differs significantly from the conventional estimate which is based on formulas valid for antennas in free space. We perform our derivations using the reciprocity theorem and the fluctuation-dissipation theorem applied to a regular electromagnetic field and a receiving antenna, which constitute the special case of a system which is not in equilibrium but allows an equilibrium (stationary state) to be reached between the incident radiation field and the electromagnetic field reemitted by the antenna. The emphasis is placed on the universal nature of the applied calculation procedure which is valid for arbitrary antennas and matters.     

碳纳米管光学天线的有效波长和谐振特性

将经典金属自由电子气模型应用于金属型碳纳米管, 基于光学天线有效波长理论, 得出了金属型碳纳米管光学天线响应的有效波长与碳纳米管介电特性之间的普适关系. 在对碳纳米管介电特性进行第一性原理计算的基础上, 以金属型4 Å碳纳米管为例, 进一步研究了金属型碳纳米管光学天线响应的有效波长与入射波长之间的关系, 以及金属型碳纳米管光学偶极子天线的谐振特性. 通过将已有传统金属光学天线和碳纳米管天线有效波长的研究结果进行对比, 验证了本文理论的正确性. 结果表明, 碳纳米管光学天线响应的有效波长与入射波长呈近似线性关系, 与传统金属材料构成的同直径光学天线相比, 碳纳米管天线显示出了更强的波长压缩能力, 并且在可见光到红外波段内易于发生谐振. 该研究方法可为碳纳米管光学天线研究提供新的思路.     

Infrared dipole antenna enhanced by surface phonon polaritons

In this Letter, we propose a gold dipole antenna formed on a SiC substrate to achieve a strong concentration of mid-IR radiation based on a synergistic integration of the IR dipole antenna and the resonance excitation of a surface phonon polariton. Numerical simulation based on the finite-difference time-domain technique shows that the intensity enhancement can be greater than 10(7) times at the mid-IR spectral region. The influence of the geometric parameters (i.e., antenna length, gap dimension, antenna thickness, and antenna width) on the antenna field enhancement is also studied. The strong intensity enhancement can find important applications in highly sensitive mid-IR photodetectors and in molecular detection and identification by surface-enhanced IR absorption spectroscopy techniques.     

基于极化旋转超表面的圆极化天线设计

本文通过设计出一种反射型极化旋转超表面,在8—12 GHz频域内实现高效的极化旋转,并将其加载于微带缝隙天线下方构成新型的极化旋转超表面天线,利用超表面的90°极化旋转效应,成功实现了天线的圆极化辐射调制.仿真与实验结果表明:圆极化天线的中心工作频率为GHz,阻抗带宽为8.3—10 GHz.当微带缝隙天线与极化旋转超表面的间距H=4.5mm时,天线在8.3—8.8 GHz频带内实现了圆极化辐射;当mm时,天线在8.8—9.3 GHz频带内实现了圆极化辐射;当=8mm时,天线在9.3—10 GHz频带内实现了圆极化辐射.实验结果与仿真结果相符,证明了此种设计方法的有效性,也为微带缝隙天线的圆极化设计提供了一种新的途径.     

Measurement of the resonant lengths of infrared dipole antennas

The resonant lengths of infrared dipole antennas at 10.6 and 3.39 μm are experimentally investigated. For this purpose, submicron-sized microbolometers coupled to dipole antennas with lengths between 0.7 and 20 μm were fabricated on a SiO₂-on-Si substrate. The response of the detector to 10.6 μm radiation shows a first resonance for an antenna length between 1.0 and 2.5 μm. A subsequent zero and a second attenuated resonance are observed as the antenna length increases. Similar behavior is observed for illumination at 3.39 μm, with a first resonance occurring at a length shorter than 1 μm. The results permit evaluation of an effective dielectric permittivity and shows the effect of the surface impedance of the metal on the propagation of current-wave on the antenna. The resonance behavior is further studied by changing the irradiation conditions of the detectors. Air-side and substrate-side illumination exhibit identical resonant antenna lengths, but different efficiencies of power collection. The antenna patterns as a function of incident angle have also been measured at 10.6 μm, showing a transition from a primary broadside lobe to the development of side lobes for longer antennas. Finally, an antenna response is measured at visible frequencies. Our measurements point out similarities, as well as differences, between infrared antennas and their counterparts at microwave frequencies, and provide insights useful for the design optimization of planar infrared antennas.     

Antenna length and polarization response of antenna-coupled MOM diode infrared detectors

This work focuses on the fabrication and response of dipole antenna-coupled metal–oxide–metal diode detectors to long-wave infrared radiation. The detectors are fabricated using a single electron beam lithography step and a shadow evaporation technique. The detector’s characteristics are presented, which include response as a function of incident infrared power and polarization angle. In addition, the effect of dipole antenna length on detection characteristics for 10.6 μm radiation has been measured to determine resonant lengths. The response of the detector shows a first resonance at a dipole length of 3.1 μm, a second resonance at 9.3 μm, and third at 15.5 μm. The zeros intermediate to the resonances are also evident.     

Plasmonic abilities of gold and silver spherical nanoantennas in terms of size dependent multipolar resonance frequencies and plasmon damping rates

Absorbing and emitting optical properties of a spherical plasmonic nanoantenna are described in terms of the size dependent resonance frequencies and damping rates of the multipolar surface plasmons (SP). We provide the plasmon size characteristics for gold and silver spherical particles up to the large size retardation regime where the plasmon radiative damping is significant. We underline the role of the radiation damping in comparison with the energy dissipation damping in formation of receiving and transmitting properties of a plasmonic particle. The size dependence of both: the multipolar SP resonance frequencies and corresponding damping rates can be a convenient tool in tailoring the characteristics of plasmonic nanoantennas for given application. Such characteristics enable to control an operation frequency of a plasmonic nanoantenna and to change the operation range from the spectrally broad to spectrally narrow and vice versa. It is also possible to switch between particle receiving (enhanced absorption) and emitting (enhanced scattering) abilities. Changing the polarization geometry of observation it is possible to effectively separate the dipole and the quadrupole plasmon radiation from all the non-plasmonic contributions to the scattered light.     

Investigation of Euler spiral nanoantenna and its application in absorption enhancement of thin film solar cell

A theoretical study on nanoantenna and its application in enhancing the performance of the thin film solar cell (TFSC) is presented. In this work, a novel design of nanoantenna i.e. Euler spiral nanoantenna (ESNA) is introduced, which has evolved after bending the conventional dipole nanoantenna in the manner of Euler spiral. The bending is performed up to an optimum length so that the antenna can equally respond to the two orthogonally polarized waves. Then the proposed nanoantenna in turnstile manner is examined for the intended application of enhancing the absorption in TFSCs. The antenna is placed on the absorber layer (Si amorphous) of the TFSC with a coating of Zinc Oxide. The simulation results show that the proposed ESNA can significantly increase the absorption in the absorber layer of the TFSC. The performance in terms of absorption and quantum efficiency of the solar cell incorporated with ESNA has been studied. ESNA confines the electric field in a larger area which results in absorption increase. The simulation results show that proposed ESNA can enhance the absorption up to 97.6% in the absorber layer and the photocurrent is enhanced by a factor of 1.39. To the best of our knowledge, this is the first study on Euler spiral nanoantenna and so as in its application with solar cells.     

金属粒子阵列共振的偏振特性

当金属纳米粒子形成规则分布且阵列周期与单粒子的共振波长近似匹配时, 会形成一种特殊的阵列共振, 这种共振比单粒子的局域表面等离子体共振具有更窄的共振线宽和更高的共振强度. 基于修正的长波近似方法, 讨论了矩形阵列的消光截面与阵列因子和单粒子的极化率之间的关系; 并详细研究了在不同偏振的入射光照射下, 阵列因子随着电偶极子方向的改变而产生的变化, 以及这一效应对阵列共振和消光截面所产生的影响. 结果表明, 大型的方阵是偏振无关的; 在矩形阵列中, 沿着阵列两个轴向的相邻粒子之间的耦合形成了阵列因子的两个极值, 并且分别对应了散射截面的最小值.     

矩形孔缝耦合特性实验研究

 对矩形孔缝在微波频率为2～18GHz范围内的耦合系数进行了实验研究；建立了实验方法和实验装置。实验结果表明：对于矩形孔缝，当入射电场方向垂直于孔缝长边时，在微波波长约等于2倍孔缝长度时，发生共振效应，在该频率附近一定带宽内耦合系数最大，并且在共振频率处存在着场增强效应。     

扇形波导谐振宽边纵缝的归一化电导

扇形波导可作为高功率微波圆柱共形波导缝隙阵天线的基本单元。分析了扇形波导中主模场分量,根据实际情况对主模场进行了合理近似。采用互易定理推导由波导主模横向场分量和缝隙场分量表示的波导场分量的前向或后向散射系数。根据波导传输线理论,将波导宽边纵缝等效为并联导纳,再根据波导边界条件得到扇形波导宽边谐振纵缝的归一化电导与波导散射系数之间的关系式。根据缝隙天线与振子天线的互补关系得到扇形波导谐振缝隙的辐射阻抗,结合波导功率平衡关系得到由波导横向场散射系数表示的缝隙辐射功率表达式,得到归一化电导的与谐振宽边纵缝的偏移位置、缝隙宽度、波导波长以及扇形波导尺寸参数之间的解析表达式。给出了算例,在波导中间区域,通过商用软件计算得到的电导与理论公式结果基本吻合。     

扇形波导谐振宽边纵缝的归一化电导

扇形波导可作为高功率微波圆柱共形波导缝隙阵天线的基本单元。分析了扇形波导中主模场分量,根据实际情况对主模场进行了合理近似。采用互易定理推导由波导主模横向场分量和缝隙场分量表示的波导场分量的前向或后向散射系数。根据波导传输线理论,将波导宽边纵缝等效为并联导纳,再根据波导边界条件得到扇形波导宽边谐振纵缝的归一化电导与波导散射系数之间的关系式。根据缝隙天线与振子天线的互补关系得到扇形波导谐振缝隙的辐射阻抗,结合波导功率平衡关系得到由波导横向场散射系数表示的缝隙辐射功率表达式,得到归一化电导的与谐振宽边纵缝的偏移位置、缝隙宽度、波导波长以及扇形波导尺寸参数之间的解析表达式。给出了算例,在波导中间区域,通过商用软件计算得到的电导与理论公式结果基本吻合。     

Manipulating near field polarization beyond the diffraction limit

We introduce a new optical nanoantenna structure with three-fold rotational symmetry. The proposed gold nanoantenna can produce a hot spot with circular polarization in the gap. The effect of the shape of the arms and geometrical imperfection on the optical response is examined. We introduce a figure of merit for practical applications that utilize the circular polarization. The figure of merit is more sensitive to changes of the geometry than the maximum near field amplitude or the maximum circular polarization. The relatively equivalent optical response of the proposed nanoantenna compared to its counterparts and its reasonable stability against small changes accompanied with its simpler structure design makes it more appropriate for experimentalists.     

Resonance fluorescence in a radio frequency field for a system of two nuclear levels

The quantum-mechanical theory of resonance fluorescence in a radio frequency (RF) field is developed for a system of two mixed nuclear levels. The case when the resonant γ ray absorption is permitted only for a single level is considered. It is shown that the bare energies of nuclear states vary simultaneously with the parameters of the mixing RF field, and an additional quasilevel appears in the system. The time-dependent probabilities of the corresponding transitions are calculated.     

Nanoparticle using parallel split rings and implementation of chain for creating Fano resonance with polarization independence for energy harvesting in mid-infrared

In optical devices, the polarization of the incident wave affects the Nano particle characteristics. Therefore, designing a polarization-independent device is significant in the process of designing optical structures. On the other hand, the concept of Fano resonance and dark mode has been utilized for achieving more energy enhancement. In this paper, we have developed a symmetrical Nano antenna by employing Fano resonance, which is independent of the incident wave polarization. The proposed Nano antenna is modified in mid infrared regime for biosensing and energy harvesting applications. The designed metamaterial antenna is made by Nano split ring resonators with etched capacitive gaps, which are utilized for concentrating energy. The introduced Nano antenna has a bright and dark mode with a weak enhancement of electric field. The effect of the incident wave polarization is investigated at wave incident angles between 0° and 45° to illustrate the independency of the polarization due to the symmetrical shape of the Nano antenna. In order to trigger the dark mode and enhance the electric field, a Nano chain is incorporated in the final structure. This arrangement has led to increasing of electric field drastically. Furthermore, the figure of merit has been calculated as an advantageous factor in sensing the surrounding materials with various refractive indices. Our findings illustrated that the chain arrangement has caused a peak in the linear form of the extinction cross section of the Nano antenna. This in turn has resulted in the appearance of Fano resonance with no impact on the resonance frequency that has been originally adjusted by capacitive gaps and inductive strips.     

共振线极化光实现原子矢量磁力仪的理论研究

共振线偏振光激发原子张量磁矩,本文理论研究在矢量磁场和射频场的共同作用下,张量磁矩进动的模型,求解刘维尔方程获得透射光时域完整解析解,包括直流、一次和二次谐波分量.研究发现:当进动的拉比频率Ω1/(22~(1/2))时,两谐波间的干涉效应使直流分量和一次谐波对称成分的单吸收峰劈裂成双峰,裂距((Ω~2+Ω~4-Ω~2-1)~(3/2))~(1/2),一次谐波反对称成分在共振处产生干涉条纹.研究结果显示,谐波间的干涉也可导致直流分量和二次谐波线宽仅为一次谐波线宽的38%,且存在磁场取向临界点,在不同的取向区间分别利用直流及两谐波共振信号辨析磁场变化,可获得最佳测磁灵敏度;同时还可通过共振时直流分量及两谐波对称成分振幅来确定磁场与激光极化方向的夹角,利用两谐波反对称成分相移的差值来确定待测磁场在垂直光极化方向投影与射频场方向的夹角,进而实现结构简单的张量磁矩进动型矢量磁力仪.这种磁力仪适合构成磁力仪阵列,可用于磁定位、水下磁异常源的检测和地磁导航等领域.     

V型纳米金球阵列天线侧向散射方向性的数值模拟

纳米天线侧向散射的方向性在生物感测以及表面增强光谱学等领域都有重要研究价值。侧向散射方向性的产生需要破坏纳米天线相对于平面波极化方向的镜像对称,由纳米粒子阵列构成的纳米天线排列灵活,易于实现非镜像对称结构。采用T-matrix方法对V型纳米金球阵列天线进行数值模拟,研究了其侧向散射的方向性,分别讨论了不同阵元数目构成的不同臂长、不同臂间开角、不同球形阵元半径、不同阵元球心间距对V型天线侧向散射方向性的影响。研究表明V型纳米阵列天线具有侧向散射方向性的可调性。     

基于Rydberg原子的超宽频带射频传感器

Rydberg原子具有极大的极化率和微波跃迁偶极矩,对外界电磁场非常敏感,可实现基于Rydberg原子的超宽频带射频电场的高分辨高灵敏测量.通过Rydberg原子的全光学无损的电磁感应透明探测手段,可以实现基于原子的快速免校准宽频带(0.01-1000 GHz)外电场的精密测量.对于频率大于1 GHz的微波场,由微波场耦合相邻Rydberg能级形成的Autler-Townes分裂进行测量;而对于频率小于1 GHz的长波射频场,由Rydberg能级的射频边带能级进行测量.这种方法是基于原子能级参数,可溯源到基本物理常量,不依赖于外界参考;且对电场无干扰,易于实现微型化和集成化,具有广泛的应用前景.本文主要综述了基于Rydberg原子的外电场测量的最新研究进展,重点介绍长波长射频场的测量,包括电场强度、频率以及极化方向的测量,详细介绍了其测量原理和探测灵敏度,并讨论了其应用前景及未来发展方向.