外在手征超材料电磁特性的研究进展

外在手征超材料作为一种结构简单,易于制造,并可以通过调整入射波的角度来动态调控电磁特性的新型超材料越来越受到人们的关注。简要介绍了外在手征超材料的背景和概念,并着重阐述了其在微波段、太赫兹波段以及光频段的数值模拟与实验研究进展。这种结构在各类光电子学器件、生物医学等领域有着现实的应用价值。     

可调谐手征超表面电磁特性研究进展

手征超表面是由具有特定电磁响应的平面手征单元结构构成的超薄超材料,由于其具有自由控制电磁波的奇异能力而引起了极大的关注.通过在超表面设计中加入可调谐材料,可以实现其功能受外部激发控制的可调谐或可重构的超器件,为动态调谐电磁波开辟了新的道路.本文介绍了可调/可重构手征超表面电磁特性的一些理论基础,当线偏振光进入可调谐手征...     

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.     

超材料对电磁波的极化转换及不对称传输研究进展

超材料新颖的电磁特性使它在许多领域都具有潜在的应用价值,如极化旋转器、类二极管等光子器件。综述了超材料中电磁波的极化转换的研究进展,包括线极化波之间、线极化波和圆极化波之间、圆极化波之间的相互极化转换,以及超材料的线极化波和圆极化波的不对称传输,并阐明了利用类Fabry-Perot谐振腔增强线极化波和圆极化波的不对称传输效应的机制。     

超表面在红外波段的光传输特性:偏振控制、旋光性和不对称传输

超表面(Metasurfaces,MMs)是拥有亚波长尺寸谐振单元结构的人工平面材料,其电磁特性主要由结构决定。超表面具有极强的波前控制能力。本文着重介绍了近年来纳米结构超表面在红外波段的光传输特性,包括光波偏振控制、旋光性、不对称传输等方面的理论和实验研究进展,简要介绍了制备纳米结构超表面的工艺技术。     

平面手征超常介质研究进展

平面手征超常介质(Planar chiral metamaterials, PCM)是近年迅速发展起来的能获得大旋光性进而控制光偏振的新颖介质.综述了PCM的研究进展,包括金属结构、全介质结构以及单层和双层结构等几种不同情况,这些PCM都能产生非常强的旋光性,在光子学中具有潜在的应用前景,并且有可能成为手征负折射光学材料中有前途的候选者.     

电磁超材料在微波吸波材料中的应用探索

人工电磁超材料具有自然界材料所不具备的电磁参数,并且拥有可设计性和可灵活调节的性质,可实现对电磁波传播性能进行新的调控,是近年来国际物理学、材料学和信息科学领域的研究热点。首先介绍了人工电磁超材料的概念内涵和近年来的发展概况,简要分析了国外人工电磁超材料研究的发展水平,以及美欧军事强国对超材料研究的重视和支持情况。重点介绍了南京大学开展的一些人工电磁超材料在微波吸波材料结构中的应用探索,包括超材料微波吸波结构的设计和分析、基于人工手征超材料结构的吸波结构设计、吸波频带可调节及可切换的微波吸波结构设计等。这些材料和结构运用人工超材料的特殊物理特性和参数的可设计性,与传统微波吸波材料相比,具有可调节的优势,有效提高了对电磁波的调控能力。     

等离子体中太赫兹波传输及成像探测特性研究

本文根据散射矩阵方法模拟等离子体并建立了非均匀等离子体理论模型,并在此基础上计算了0.1 THz^10 THz频段的全波段太赫兹波在其中的传输特性。根据介质阻挡放电原理在实验室环境下搭建等离子体射流产生装置并产生非均匀等离子体,进行了太赫兹时域光谱(THz-TDS)以及宽带太赫兹源在等离子体中的透射光谱测量以及太赫兹波对等离子体遮挡下目标物的反射成像的试验。理论和实验结果均表明,较高频太赫兹波在等离子体中有良好的穿透性,这为太赫兹波在黑障区的通信以及雷达探测应用打下研究基础。     

超表面的电磁特性研究进展

超表面由于具有自然界不存在的独特电磁特性而引起了人们极大的兴趣,它是占有更少物理空间,提供更小损耗,更容易被制造的一类超材料。简要介绍了超表面的概念和背景,并着重阐述了超表面结构在微波段、太赫兹波段以及光频段的模拟计算及实验研究进展。这些超表面在微波、光波、光电子器件中具有潜在的应用价值。     

一种硅埋置型系统级封装中集成毫米波无源器件工艺

本文研究了一种基于低阻硅埋置腔体和BCB/Au金属布线的系统级封装技术,改进了介质层BCB在有腔体硅衬底上的第一次旋涂工艺。利用25um厚的BCB介质层,在低阻硅衬底上设计、制作了微带传输线(MSL)、接地共面波导线(CPWG),测试发现具有理想的传输性能:标准50欧姆微带传输线,在20-30GHz频带内插入损耗小于0.08dB/mm,回波损耗大于32dB/mm。在此基础上基于薄膜微带线结构设计、制作了一种应用于K波段雷达前端系统集成功分器,面积约为1.6×0.84mm~2,插入损耗小于0.45dB,端口回波损耗大于25dB。     

Transference of SH waves through irregular interface between corrugated piezoelectric layer and prestressed viscoelastic substrate

An exact approach is used to investigate the horizontally polarized shear wave in an irregular piezoelectric layer with corrugated surface lying over prestressed viscoelastic substrate. Perturbation technique is used to solve the problem. Dispersion relations are obtained in closed form for electrically open and short cases. The main feature of the present work is its ability to investigate the effect of irregularity, corrugation, dielectric constant, piezoelectric constant, initial stress and viscoelastic parameter on the phase velocity of SH wave. Numerical example has been carried out to observe the profound effect of these affecting parameters on phase velocity of SH wave.     

On the Way to Experimental Test of the Time Reversal Invariance in the Nuclear Reactions

Time (T) violation can be related with charge-parity (CP) violation through the CPT theorem. The CP violation was discovered experimentally in the K₀-meson decays about 35 years ago. The T violating interaction related with the CP violation violates parity as well. However, an extension of the theory beyond the locality of the interactions might violate the CPT theorem. The result of the CPLEAR experiment [1], which has given direct evidence of T violation in the elementary-particle phenomena, could be considered under assumption of the CPT invariance.     

A Ramsey’s Method With Pulsed Neutrons for a T-Violation Experiment

A Ramsey’s method with pulsed neutrons is discussed for neutron spin manipulation in a time reversal (T) symmetry violation experiment. The neutron spin (s_n) is aligned to the direction of a vector product of the nuclear spin (I) and the neutron momentum (k_n) for the measurement of a T-odd correlation term, which is represented as s_n · (k_n × I), during propagation through a polarized nuclear target. The phase control and amplitude modulation of separated oscillatory fields are discussed for the measurement of the T-odd correlation term.     

偏振状态下球形粒子的散射相位函数研究

本文根据散射相位函数的定义,得到了偏振状态下单个粒子散射相位函数的表达式,并且通过研究发现以下规律:1)粒子半径越小,极值差随散射角越趋向于对称分布;2)散射角在0～0.025π以及O.997π～π之间,散射相位函数随极化角基本不变;3)散射角在O.025π～0.997π之间,散射相位函数随极化角变化明显.同时比较了偏振状态下多粒子和单粒子散射相位函数随散射角和极化角的分布.最后从大气中光传输理论出发,建立了非偏振状态与偏振状态下散射相位函数的关系,为大气散射回波功率测量以及近似散射相位函数的研究提供参考.     

Description of the propagation of a radially polarized beam with the scalar Kirchhoff diffraction

Since radially polarized beams have only one magnetic field component, the azimuthal component, a scalar Kirchhoff diffraction integral can be used to describe the propagation of the magnetic field. In the far-field zone, this diffraction formula gives an analytic expression for the magnetic field from which the electric field component expressions are derived by the Faraday relation. Numerical results from these expressions correctly reflect the properties of a radially polarized beam.     

Enantiomeric MOF Crystals Using Helical Channels as Palettes with Bright White Circularly Polarized Luminescence

The host–guest chemistry of metal–organic frameworks (MOFs) has enabled the derivation of numerous new functionalities. However, intrinsically chiral MOFs (CMOFs) with helical channels have not been used to realize crystalline circularly polarized luminescence (CPL) materials. Herein, enantiomeric pairs of MOF crystals are reported, where achiral fluorophores adhere to the inner surface of helical channels via biology-like H-bonds and hence inherit the helicity of the host MOFs, eventually amplifying the luminescence dissymmetry factor (g_lum) of the host l /d -CMOF (±1.50 × 10⁻³) to a maximum of ±0.0115 for the composite l /d -CMOF⊃fluorophores. l /d -CMOF⊃fluorophores in pairs generate bright color-tunable CPL and almost ideal white CPL (0.33, 0.32) with a record-high photoluminescence quantum yield of ≈30%, which are further assembled into a white circularly polarized light-emitting diode. The present strategy opens a new avenue for propagating the chirality of MOFs to realize universal chiroptical materials.     

Emergent Nonreciprocal Circularly Polarized Emission from an Organic Thin Film

Controlling circularly polarized (CP) emission is key for both fundamental understanding and applications in the field of chiral photonics and electronics. Here, a completely new way to achieve this goal is presented. A luminescent thin film, made from a chiral conjugated phenylene bis-thiophenylpropynone able to self-assemble into ordered structures, emits highly circularly polarized light with opposite handedness from its two opposite faces. Such emergent nonreciprocal behavior in CP emission, so far unprecedented, represents a fundamental advance, opening new opportunities in design, preparation, and applications of CP emitting materials.     

Fabrication of laser induced periodic surface structure for geometrical engineering

The paper presents the highly ordered geometrical structures of laser induced periodic surface structure (LIPSS) in azobenzene urethane polymer (DR19 polymer) from 4-(N,N-dihydroxyethylamino)-4′-nitroazobenzene (Disperse red 19) with tolylene-2,4-diisocyanate (TDI). One or two regulated striped LIPSS was formed in confined spaces between surface relief gratings (SRG) induced by the s-polarized interfered beams. The pitch of LIPSS was one-half or one-third of SRG pitch. Standing wave with some selected mode between SRG in the surface waveguide is responsible for the formation of the regulated striped LIPSS. The crossed illumination of the interfered beams showed the waffle-like structure for s-polarization beam and the egg crate-like (ECL) structure for p-polarized beam. Photoinduced microscopic molecular ordering was also investigated. The linear polarized beam gave the large optical anisotropy in the polymer and the circularly polarized beam produced the chiral structure. The circular dichroism spectra showed the sharp peak due to the circular Bragg reflection from which the chiral pitch was evaluated.     

Feasibility study of in-beam polarization of fluorine

The feasibility of in-beam polarization of nuclear spin in F⁺ beams was studied. It was demonstrated that metastable atomic fluorine could be optically pumped on the closed transition (3s ⁴P_5/2→3p ⁴D_7/2) at 686 nm. The metastable production efficiency in sodium vapor was measured using optical depopulation pumping of the metastable on the (3s ⁴P_5/2→3p ⁴D_5/2) transition at 678 nm. At low helium density, 0.24 (+0.16/−0.03) of the reionized beam was derived from metastables, implying an ion beam polarization of 24% would be feasible if the metastables were fully polarized. The hyperfine structures of the 3s ⁴P_5/2, 3p ⁴D_5/2 and 3p ⁴D_7/2 states in ¹⁹F were measured via laser-induced fluorescence and modulated optical depopulation pumping. Based on these results, a scheme is suggested for polarizing ²⁰F.