同时实现介电常数和磁导率为负的H型结构单元左手材料

基于用一种结构同时实现材料介电常数和磁导率为负的思想，提出了H型结构单元左手材料模型.采用矩形波导法测试表明，H型结构单元在微波频率范围出现左手透射峰，并且可以由参数t对左手特性区域进行调控.同时利用相位法、棱镜折射法和散射参量法从实验和理论证明了在左手透射峰区域材料的折射率为负值，介电常数和磁导率亦同时为负.相对由金属开口谐振环与金属线两种结构组合实现的左手材料，H型结构集磁谐振与电谐振于一体，结构简单、制备方便，对微波器件左手材料表现出更多的优越性.     

Spectral control in anisotropic resonance-domain metamaterials

We introduce a concept to control the spectral and dichroic properties of metamaterials. The approach is based on anisotropic metal nanoparticles and on varying their mutual orientation in a periodic lattice. Even seemingly inconsequential changes in particle ordering strongly modify the dichroic properties of the arrays and result in either very narrow resonances or ultrabroad extinction ranges. The results arise from long-range diffractive coupling between the particles, as determined by the dependence of the array unit cell size on particle ordering.     

内混合强吸收气溶胶粒子光散射的等效性

 以黑碳和水两种成分组成的内混合单分散气溶胶粒子为例,根据其各消光效率因子、吸收效率因子和散射相函数,分析了用等效折射率来描述含有不同成分的内混合气溶胶系统的适用性。结果表明：在瑞利散射区和几何光学区内,内核（碳粒）体积比为0.01,0.1,0.5,0.9时,消光效率在大多数尺度参数下等效性都很好,但在米散射区内相对较差;当体积比大于0.3时,其吸收效率、消光效率等效性较好;除瑞利散射区外,散射相函数在各体积比下的等效性都很差。当考虑内混合气溶胶粒子系统的散射和吸收特性时,一般不难找到等效折射率,但在光散射技术中,应用相函数反演等效折射率的可靠性还有待商榷。     

Ensembles of plasmonic nanospheres at optical frequencies and a problem of negative index behavior

Arrays of metallic nanoparticles support individual and collective plasmonic excitations that contribute to unusual phenomena like surface-enhanced Raman scattering, anomalous transparency, negative index, and subwavelength resolution in various metamaterials. We examined the electromagnetic response of dual Kron’s lattice and films containing up to three monolayers of metallic nanospheres. It appears that open cubic Kron’s lattice exhibits ‘soft’ electromagnetic response but no negative index behavior. The close-packed arrays behave similarly: there are plasmon resonances and very high transmission at certain wavelengths that are much larger than the separation between the particles, and a ‘soft’ magnetic response, with small but positive effective index of refraction. It would be interesting to check these predictions experimentally. PACS 78.20.Ci; 42.30.Wb; 73.20.Mf; 42.25.Bs     

Coherent Transmission and Reflection by a monolayer of discrete scatterers

Coherent transmission and reflection of a plane wave through a monolayer of discrete particles are considered on the basis of simple and physically transparent formulae for the single scattering approximation (SSA) corrected by introducing a multiple scattering permittivity factor. This factor allows for multiple scattering of Waves between monolayer particles, opposite to the SSA. The multiple scattering permittivity factor is considered on the basis of the quasi-crystalline approximation (QCA) via ? matrix formalism. The multiple scattering permittivity factor and parameters for obtaining coherent transmission and reflection coefficients (the effective extinction coefficient and the transmission and reflection coefficients due to rescattering) are calculated within the scope of QCA and plotted for comparison with SSA results. The expressions for these values are simplified for small Rayleigh particles to simple analytical formulae.     

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基于Mie散射理论和方法,研究了航天器尾喷焰等离子体中Al2O3粒子的光学散射特性,分析了复折射率对单个Al2O3粒子消光效率因子、散射效率因子、吸收效率因子、散射相函数以及单次反照率的影响。同时,基于多分散系粒子尺度单峰分布,分析了Al2O3粒子按粒径分布后散射场的有关效应因子及散射相函数的变化,并进行了相应的数值模拟。理论和数值模拟研究表明,航天器尾喷焰等离子体Al2O3粒子复折射率的虚部和实部、粒径的大小与分布对其散射相函数、消光和散射效率因子以及单次反照率均有明显的影响。     

基于聚酰亚胺基底的太赫兹滤波器

超材料是通过人工方式做成的具有特殊电磁特性的亚波长周期性金属结构,通过合理的设计样品结构,可以实现自然界中传统材料无法实现的电磁现象。超材料可以广泛用于电磁隐身、完美吸收、负折射率等研究领域,近些年,随着太赫兹技术的发展,太赫兹超材料器件被广泛研究。由于硅（Si）对于太赫兹波的透过率较高,通常选取Si作为基底材料。但Si硬度较高、不易弯曲且易碎等缺点限制了THz超材料的应用。聚合物材料聚酰亚胺具有柔性,作为基底,克服了传统硅基底的缺点,透过率可以与Si匹敌,而且其表面光滑,适合传统光刻技术加工。对聚酰亚胺在太赫兹波段光学性质的测试结果表明,此种材料的折射率在1.9左右,透过率达到80%以上。设计了一种双开口谐振环结构,研究了其太赫兹波透射性质以及随太赫兹波的入射角度和样品曲率的变化规律,发现透射峰强度和峰位均不发生改变。此结果展示了将平面滤波延伸到曲面滤波领域的可能性,若将聚酰亚胺基底做薄,为今后太赫兹频段隐身衣的研究提供基础。将不同结构的两种样品叠加在一起制成宽谱滤波器, 50%的带宽达到181 GHz。此种宽带滤波器制作简单,滤波效果显著,为太赫兹波段宽带滤波器的制作提供一种新思路。     

相对湿度对大气气溶胶消光系数的影响

消光系数是气溶胶颗粒物光学性质的关键参数之一。基于Mie散射理论和气溶胶颗粒粒径及折射率的湿度增长模型,本文详细研究了气溶胶吸湿性对其消光系数的影响。计算结果表明:当入射光波长为808nm、相对湿度在60%~95%之间增加时,因颗粒粒径的增长及折射率的减小,导致颗粒物消光系数曲线右移且其波动性更加明显;而对于同一球形颗粒,小粒径颗粒的消光系数随相对湿度的增加呈指数规律增大,较大粒径颗粒的则表现为波动减小趋势。此外,在不同入射光条件下,小颗粒消光系数与相对湿度之间的关系保持不变。本文的计算结果对气溶胶光学性质与大气环境质量的研究具有一定的参考价值。     

大气气溶胶消光特性和折射率的测量

 介绍了一种综合利用能见度仪、微脉冲激光雷达和光学粒子计数器测量大气气溶胶折射率的新方法。首先使用能见度仪和激光雷达测量出大气气溶胶的消光系数和消光后向散射比,然后使用粒子计数器测量出粒子谱分布,结合气溶胶粒子折射率,根据球形粒子的米（Mie）散射理论,可以得到气溶胶消光系数和消光后向散射比。通过分析消光系数、消光后向散射比、粒子谱分布和折射率之间的关系,结合已知的消光系数和消光后向散射比,反演出大气气溶胶粒子的折射率。     

A Light Scattering Instrument for Sizing Mixtures of small and large particles

An instrument is proposed for the visualisation and measurement of mixtures of small and large particles. The original concept was to use spectral extinction for sub-micron particles and scattering patterns for larger sizes. However, the former method is sensitive to the refractive index, which may be unknown or vary with wavelength in an unknown way. The experiments demonstrated this to be a problem. The forward scatter, on the other hand, is not so sensitive to this. It is shown here that the combination of scattered intensity as a function of both angle and Wavelength provides scatter diagrams for which there is good agreement between theory and experiment. The influence of quite small volume fractions of particles as small as 0.3μm mixed with 90μ particles is easily seen. The scatter diagrams suggest the use of image analysis for size measurement and quality control.     

在溴化钾粉末中掺入大量α-炭化硅压片的异常红外透射光谱研究

在光谱学实践中，通常由于带测样品颗粒在本征吸收峰附近产生可观的附加散射消光，致使表观吸收峰偏离实际位置，从而得到不的光谱，这就是我们常要采取措施尽量避免的克里斯坦森（Christiansen）效,这一就是在制作压片（例如溴化钾）时，待测样品含量要少（少于2％）。在一次实验中，当在KBr粉末中掺入大量（而非正常要求的少许）的α-SiC微粉后，得到了一个在1052.33cm^-1处有一个尖峰的中红外透射谱。我们发现，这个新现象非常有趣，它与克里斯坦森效应表面上相反，但都可用Lorentz色散模型给予精确地解释。于是称它为反克里斯坦森效应，在该效应出现的频率处两种材料的折射率相等，且吸收系数都非常小。这个新现象也非常有意义，它可用来制造新型的带通滤波器以及准确测定某些材料的折射率等。     

银纳米颗粒复合超材料的数值和模拟研究

理论分析了单层银纳米颗粒及其复合超材料的电磁特性,并采用MATLAB数值计算和CST模拟对理论进行了验证.结果显示:4.75 nm银颗粒所形成的单层阵列的数值和模拟结果都有Lorentz共振效应出现,模拟结果相对于数值计算有红移现象,且有微弱的磁共振效应.进一步对采用4.75 nm颗粒复合而成的100 nm大颗粒模拟,结果表明:在800~1 000 nm区间共振得到负的实有效介电常量、负的实有效磁导率和负的折射率,说明100 nm复合球形颗粒具有很强的磁共振效应,与理论分析相符.     

The scattering matrix for size distributions of irregular particles: An application to an olivine sample

We have compared simulated and measured scattering matrices of a size distribution of olivine particles at wavelengths of 633 and 442 nm. The computations were carried out for size distributions of irregularly-shaped compact particles with different average projected areas using the discrete-dipole approximation (DDA). The results of the comparison show that the model of irregularly-shaped particles mimic the observations far better than the results given by spheres, spheroids or rectangular prisms having a wide range in aspect ratios. The computed scattering matrices for size distributions of irregularly-shaped particles do not depend very strongly on the precise particle shape assumed, providing a method to infer certain physical properties of an ensemble of natural dust particles, such as the refractive index, when some information on the sample, as the size distribution, is known a priori.     

Study of the sensitivity of size-averaged scattering matrix elements of nonspherical particles to changes in shape, porosity and refractive index

Studies of the physical parameters that influence the single scattering properties of a size distribution of small particles in random orientation are fundamental in understanding the origin of the observed dependence of the scattering matrix elements on the scattering angle. We present results of extensive calculations of the single scattering matrices of small nonspherical particles performed by a computational model based on the Discrete-Dipole Approximation. We have particularly studied the sensitivity of the size-averaged scattering properties at visible wavelengths of nonspherical, randomly oriented absorbing particles considering changes in shape, porosity and refractive index. These studies have importance regarding the inversion of physical properties of small particles as measured in the laboratory and the dust properties in various astrophysical and atmospherical environments. We have found that size distributions of randomly oriented irregular particles of different shape, including large aspect ratio particles, show similar scattering matrix elements as a function of the scattering angle, in contrast with the pattern found for regularly shaped particles of varying axis ratios, for which the scattering matrix elements as a function of the scattering angle show much larger differences among them. Regarding porosity, we have found a very different pattern in the scattering matrix elements for an ensemble of compact and porous particles. In particular, the linear polarization for incident unpolarized light produced by compact and absorbing particles of large size parameter tend to mimic the pattern found for large absorbing spheres. For porous particles, however, the linear polarization for incident unpolarized light tends to decrease as the size of the particle grows, with the maximum being displaced towards smaller and smaller scattering angles.     

电谐振器和磁谐振器构成的左手材料的实验验证

加工、制作和测试了由电谐振器和磁谐振器构成的左手材料.首先分别测试了电谐振器、磁谐振器各自的传输频谱,得到各自的负参数区域,然后测试了由电谐振器和磁谐振器构成的左手材料的传输频谱,并提取了其等效介电常数和磁导率.实验结果表明,在电谐振器和磁谐振器各自传输禁带的重合区域,出现了一个通带,在该通带内,等效介电常数和磁导率同时为负,验证了材料的左手特性.     

Evaluation of Influence of Multiple Scattering Effect in Light-Scattering-Based Applications

The extinction cross sections of a system containing two particles are calculated by the T-matrix method, and the results are compared with those of two single particles with single-scattering approximation. The necessity of the correction of the refractive indices of water and polystyrene for different incident wavelengths is particularly addressed in the calculation. By this means, the volume fractions allowed for certain accuracy requirements of single-scattering approximation in the light scattering experiment can be evaluated. The volume fractions calculated with corrected refractive indices are compared with those obtained with fixed refractive indices which have been rather commonly used, showing that fixed refractive indices may cause significant error in evaluating multiple scattering effect. The results also give a simple criterion for selecting the incident wavelength and particle size to avoid the ＇blind zone＇ in the turbidity measurement, where the turbidity change is insensitive to aggregation of two particles.     

An anomalous change in the frequency of plasmon resonances of island metal films upon their contact with some polar organic media

We have examined the changes in the extinction of island metal films that occur as a result of their contact with a liquid crystal or polymethylmethacrylate. The morphology of surface nanostructures has been investigated. We have revealed that, upon immersion of an island metal film into a liquid medium molecules of which are polar, the shift of the plasmon resonance in the extinction spectrum and the increase in the extinction at the frequency of this resonance can substantially differ from the shift and the extinction increase theoretically calculated for an isotropic surrounding substance. We have shown that the reason for these differences is the local anisotropy of the refractive index of the medium in the immediate vicinity of metal particles, which is determined both by the shape of particles and by the degree of occupation of the substrate surface.     

利用集总L-C元件构造的一维metamaterials特性的实验研究

在普通微带传输线中周期性地加载集总L C元件能够构造一维特异性材料(metamaterials)，它具有与众不同的特异性质.通过实验证实了波在这种结构中传播具有相速度与群速度方向相反的左手性通带，其折射率为负值，并发现平均折射率为零的能隙.这种结构具有结构紧凑，参数可调，制作简单的优点. 关键词： 负折射率 特异性材料 周期性结构 微带线     

Tunable dual-band infrared chiral metamaterials based on double-layered asymmetric U-shape split ring resonators

We have numerically demonstrated chiral metamaterials based on double-layered asymmetric U-shape split ring resonators. Dual-band circular dichroism is found in the whole frequency regime from 50 to 250 THz by studying the transmission properties. Huge optical activity and the induced negative refractive index are obtained at resonance by calculating the optical activity and ellipticity of the transmitted E-fields. Chirality parameter and effective refractive index are retrieved to illustrate the tunable optical properties of the metamaterials. The underlying mechanisms for the observed circular dichroism are analyzed. These metamaterials would offer flexible electromagnetic applications in the infrared regime.     

颗粒系的可见消光光谱分析及最佳波长的选择

在光全散射法颗粒粒径测量中,被测颗粒系的消光光谱包含有颗粒粒径、折射率等信息。对常用的单峰及双峰R-R分布的可见消光光谱进行模拟,分析了可见消光光谱随粒径和相对折射率变化的规律。选取二阶微分可见消光光谱不连续点对应的波长作为测量波长,并将可见光边界波长同时作为测量波长,在非独立模式下,采用遗传优化算法反演粒径分布。仿真计算与实验验证结果表明,通过消光光谱分析,可以预先确定被测颗粒系的分布状况,缩小优化算法中反演参数的搜索范围。结合最佳波长选择方法,使测量的精度和可靠性明显提高。对测量光谱加入1%随机噪声时,单峰及多峰分布粒径反演均能得到满意的结果。