不同结构碳黑填充的复合体系的太赫兹时域光谱研究

利用熔融共混、压片的方法制备了两种不同结构的碳黑(乙炔碳黑和高结构碳黑)填充的高密度聚乙烯复合材料,并利用太赫兹时域光谱研究了复合体系在太赫兹波段的介电性质.研究发现,随着频率的增加,体系的吸收系数逐渐增大而折射率则逐渐降低;在相同的频率下,吸收系数和折射率均随颗粒浓度的增加而增大;与乙炔碳黑相比,相同浓度的高结构碳熙填充的复合体系具有较大的吸收系数和较低的折射率,这与碳黑的颗粒结构以及颗粒间的团聚状态是紧密相关的.假定复合体系的介电损耗是由碳黑颗粒内部载流子的极化和聚乙烯基体的界面极化所导致的,利用双德拜模型对实验结果进行了解释,分别得到了两种极化模式所对应的弛豫时间和弛豫强度等信息.     

Kramers-Kronig relations and sum rules of negative refractive index media

Negative refractive index media have become a hot topic in physics due to their proposed revolutionary properties, which would have drastic consequences in design of novel optical devices. We show that Kramers-Kronig relations connecting the real and imaginary parts of the complex refractive index of absorbing media are valid even though the real refractive index may take negative value at some spectral range. In addition universal sum rules for linear optical constants of negative index media are also valid. This means that negative refractive index media are not fundamentally different from regular media. Hence, any spectrum measured from negative refractive index media can be analyzed using dispersion relations and sum rules, which have so far provided information on the optical properties of materials.Received: 13 May 2004, Published online: 30 September 2004PACS: 77. Dielectrics, piezoelectrics, and ferroelectrics and their properties - 78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)     

Optical Properties of Nano 5,10,15,20-Tetraphenyl-21H,23H-Prophyrin Nickel (II) Thin Films

Optical properties of the as-deposited and annealed films of 5, 10, 15, 20-Tetraphenyl-21H, 23H-Porphyrin nickel (II), (NiTPP) were investigated using spectrophotometric measurements of both transmittance and reflectance at normal incidence of light in the wavelength range, 200–1100 nm. The obtained data of refractive index, and absorption index, were used to estimate the type of transition and both optical and fundamental gaps. The normal dispersion (λ > 600 nm) of refractive index is discussed in terms of single oscillator model of Wemple-Didomenico, while the anomalous dispersion (λ < 600 nm) is discussed according to multi oscillator. The dispersion parameters; oscillator energy, dispersion energy, optical dielectric constant at higher frequency, lattice dielectric constant, and the ratio of carrier concentration to the effective mass N/m* were determined. The real part of the dielectric constant, the imaginary part of the dielectric constant, the loss factor, the volume and the surface energy loss functions were estimated and discussed.     

1维光子晶体缺陷模

 利用光学传输矩阵理论对掺杂1维光子晶体的缺陷模进行了研究。计算和分析了缺陷层折射率、缺陷层厚度与缺陷峰的关系。得出结论：随着缺陷层厚度的增大,缺陷峰波长呈线性增加,但是当缺陷层厚度增加到一定值时,缺陷峰的个数也将不断增加;缺陷层折射率也与缺陷峰波长有线性正比关系。从而提出了一种在微波领域测量介质折射率和介电常数的有效方法。     

吸收介质膜/金属空芯光纤的太赫兹波传输特性

介质/金属结构空芯光纤是一种有发展前景的太赫兹波传输媒质.介质膜在有效增加内面反射率从而降低传输损耗的同时,其材料吸收会引起附加损耗.讨论了介质材料吸收对太赫兹空芯光纤结构参数的影响.计算结果表明,相比于无吸收的理想介质,吸收介质的最优膜厚变小.最优折射率变大.综合考虑了光纤内直径、介质膜折射率和传输波长等因素,分析了介质膜的材料吸收容限.分析结果表明,吸收容限随光纤内直径减小或传输波长增大而减小.当光纤内直径很小或传输波长很大时,吸收容限可能不存在.分析结果对介质/金属太赫兹空芯光纤的设计和材料选择具有重要参考价值.     

Effect of particles size on the optical constants of iron/polystyrene composites via UV-radiation

The present study deals with the optical characteristics of polystyrene (PS) composites containing iron particles of different sizes: 5, 40, 110, and 250 μm. The optical absorption spectra were collected in the wavelength range 300–800 nm using a UV-spectrophotometer. The optical results obtained were analyzed in terms of the absorption formula for non-crystalline materials. The optical energy gap and other basic optical constants such as refractive index, dielectric constants, and optical conductivity were investigated and showed a clear dependence on the iron particles size. It was found that the optical energy gap for the iron-filled composites is less than that for the neat PS, and it decreases as the iron particle size decreases. The refractive index of the prepared composites was determined from the collected transmittance and reflectance spectra. It was found that the calculated dielectric constant and refractive index of the composites increase when the iron particles size decreases. The optical dispersion behavior of the composites was described by the single-oscillator model. Enhancement in the optical conductivity was observed with decreasing the iron particles size.     

双层介质球体所受光作用力的分析与计算

计算了双层介质球体的光作用力.结果表明,双层结构内外层相对折秧经和相对厚度的变化都将影响光作用力的大小.特别是当内层折射率大于外层折射率时,减小内层半径可得到一较小区域,在此区域光镊系统刚度将得到有效提高,可实现对双层介质球体的稳定束缚;而当内层折射率小于外层折射率时,随内层半径的减小,介质小球可能有两个稳定平衡点出现.     

Design of near-unity transmittance dielectric/Ag/ITO electrodes for GaN-based light-emitting diodes

We designed a near-unity transmittance dielectric/Ag/ITO electrode for high-efficiency GaN-based light-emitting diodes by using the scattering matrix method. The transmittance of an ultrathin metal layer, sandwiched between a dielectric layer and an ITO layer, was investigated as a function of the thickness and the optical constant of each constituent layer. Three different metals (Ag, Au, and Al) were examined as the metal layer. The analytical simulation indicated that the transmittance of a dielectric/metal/ITO multilayer film is maximized with an approximately 10-nm-thick Ag layer. Additionally, the transmittance also tends to increase as the refractive index of the upper dielectric layer increases. By tailoring the thickness of the dielectric layer and the ITO layer, the dielectric/Ag/ITO structure yielded a transmittance of 0.97, which surpasses the maximum transmittance (0.91) of a single ITO film. Furthermore, this extraordinary transmittance was present for other visible wavelengths of light, including violet and green colors. A complex phasor diagram model confirmed that the transmittance of the dielectric/metal/ITO multilayer film is influenced by the interference of reflected partial waves. These numerical findings underpin a rational design principle for metal-based multilayer films that are utilized as transparent electrodes for the development of efficient light-emitting diodes and solar cell devices.     

介质/金属结构太赫兹空芯光纤的传输特性

理论分析了金属、介质/金属结构空芯光纤在THz波段的模式结构和传输特性.金属空芯光纤支持TE11模式,介质/金属空芯光纤的介质膜厚在取最优值时支持HE11模式.对于波长为200μm的太赫兹波,内径为1 mm的两种空芯光纤,TE11和HE11模式的损耗分别为8.4 dB/m和2 dB/m.为优化介质/金属结构宅芯光纤的传输性能,分析了金属和介质材料的光学常数对衰减系数的影响.基于几种已发表的金属在太赫兹波段的光学常数,计算结果表明铝是最好的选择;初步测量结果显示,在各种树脂材料中聚乙烯在THz波段吸收较小,并且其折射率接近介质膜的最优值1.41,为太赫兹波空芯光纤中介质膜材料的理想选择.     

含有吸收材料对称结构一维三元光子晶体的透射谱

利用传输矩阵法理论,研究含吸收材料对称结构一维三元光子晶体的光传输特性。结果表明:当各层介质无吸收时,在较宽的禁带范围内出现一条透射率为100%的透射峰;当介质的折射率为带有正虚部的复数,即介质存在吸收时,禁带中的透射峰出现明显的透射衰减,且随着复折射率虚实比β的增大透射率出现单调衰减规律;当单个介质存在吸收时,随着各介质折射率虚实比的增大,透射率的衰减速度存在各异,其中以C介质的折射率虚实比βc对透射峰透射率的影响较大,其次为B,A的影响相对较小;当所有介质同时存在吸收时,透射衰减最为明显。这些特性为光学衰减器的设计提供理论指导意义。     

Effect of the concentration of magnetic grains on the linear-optical-absorption coefficient of ferrofluid-doped lyotropic mesophases: Deviation from the Beer-Lambert law

In this paper is reported a systematic experimental study of the linear-optical-absorption coefficient of ferrofluid-doped isotropic lyotropic mixtures as a function of the magnetic-grains concentration. The linear optical absorption of ferrolyomesophases increases in a nonlinear manner with the concentration of magnetic grains, deviating from the usual Beer-Lambert law. This behavior is associated to the presence of correlated micelles in the mixture which favors the formation of small-scale aggregates of magnetic grains (dimers), which have a higher absorption coefficient with respect to that of isolated grains. We propose that the indirect heating of the micelles via the ferrofluid grains (hyperthermia) could account for this nonlinear increase of the linear-optical-absorption coefficient as a function of the grains concentration.Received: 16 December 2003, Published online: 27 April 2004PACS: 61.30.-v Liquid crystals - 83.80.Qr Surfactant and micellar systems, associated polymers - 78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)     

Intersubband optical absorption coefficients and refractive index changes in a parabolic cylinder quantum dot

Optical absorption coefficients and refractive index changes associated with intersubband transition in a parabolic cylinder quantum dot are theoretically investigated. In this regard, the electronic structure of the dot is studied using the one band effective mass theory, and by means of the compact-density matrix approach the linear and nonlinear optical absorption coefficients and refractive index changes are calculated. The effects of the size of the dot, optical intensity and electromagnetic field polarization on the optical absorption coefficient and refractive index changes are investigated. It is found that absorption and refractive index changes are strongly affected not only by the size of the dot but also by optical intensity and the electromagnetic field polarization.     

Light Absorption of GaN Nanowire Array Cathode with Alkali Metal Nanoparticle Modified on the Surface

Since the adsorption of alkali metals is necessary for the negative electron affinity (NEA) of the photocathode, light absorption models of GaN nanowire (NW) arrays with alkali metal (Li, Na, K, and Cs) nanoparticles (NPs) modified on the NW surface based on the finite difference time domain (FDTD) method are constructed. The absorption spectra of hemispherical, spherical alkali metal NPs adsorbed on the outer surface of the NW, and spherical alkali metal embedded on the inner surface and center of the NW are studied. When the ratio of NW diameter to period (D/P) is greater than 0.5, the adsorption of alkali metal NPs cannot improve the absorption of GaN NW arrays. Alkali metal decoration can cause the absorption gain of NW arrays and optical loss of NPs, so the diameter and spacing of alkali metal NPs need to be balanced. When Li NPs are embedded in NW, plasmons can enhance the generation of electron-hole pairs, making GaN NWA obtain higher optical absorption and quantum efficiency. Therefore, the method of Li and Cs NPs embedded in GaN NW can provide a reference for the process NEA design, which will contribute to the development of the ultraviolet photocathode with high absorption characteristics.     

Dependence of film thickness on the structural and optical properties of ZnO thin films

ZnO thin films are prepared on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) at room temperature. Optical parameters such as optical transmittance, reflectance, band tail, dielectric coefficient, refractive index, energy band gap have been studied, discussed and correlated to the changes with film thickness. Kramers-Kronig and dispersion relations were employed to determine the complex refractive index and dielectric constants using reflection data in the ultraviolet-visible-near infrared regions. Films with optical transmittance above 90% in the visible range were prepared at pressure of 6.5 × 10⁻⁴ Torr. XRD analysis revealed that all films had a strong ZnO (0 0 2) peak, indicating c-axis orientation. The crystal grain size increased from 14.97 nm to 22.53 nm as the film thickness increased from 139 nm to 427 nm, however no significant change was observed in interplanar distance and crystal lattice constant. Optical energy gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. The transmission in UV region decreased with the increase of film thickness. The refractive index, Urbach tail and real part of complex dielectric constant decreased as the film thickness increased. Oscillator energy of as-deposited films increased from 3.49 eV to 4.78 eV as the thickness increased.     

Al2O3薄膜/纳米Ag颗粒复合结构的光吸收谱及增强Raman散射光谱研究

Al₂O₃介质薄膜与纳米Ag颗粒构成的复合结构,被应用于表面增强Raman散射探测实验中,其中Al₂O₃介质薄膜对纳米Ag颗粒的吸收谱及增强Raman散射光谱的影响被特别关注.该复合结构的光学特性表征出纳米Ag颗粒的偶极振荡特性.从光吸收谱中可以看到,其共振吸收谱随Al₂O₃介质薄膜厚度增加而在整个谱域上发生红移,表明纳米Ag颗粒的周围介电常数随Al₂O₃介质薄膜厚度的增加而增大.采用罗丹明6G作为探针原子,6个Raman特征峰的平均增益值作为表征表面增强Raman散射衬底增益程度的量度.实验结果表明,Al₂O₃介质薄膜层的引入提高了纳米Ag颗粒的衬底介电常数,并引起了散射共振的增强,从而使表面增强Raman散射强度提高. 关键词： 纳米Ag薄膜 共振吸收 表面增强Raman散射 介电常数     

Al2O3薄膜/纳米Ag颗粒复合结构的光吸收谱及增强Raman散射光谱研究

Al₂O₃介质薄膜与纳米Ag颗粒构成的复合结构,被应用于表面增强Raman散射探测实验中,其中Al₂O₃介质薄膜对纳米Ag颗粒的吸收谱及增强Raman散射光谱的影响被特别关注.该复合结构的光学特性表征出纳米Ag颗粒的偶极振荡特性.从光吸收谱中可以看到,其共振吸收谱随Al₂O₃介质薄膜厚度增加而在整个谱域上发生红移,表明纳米Ag颗粒的周围介电常数随Al₂O₃介质薄膜厚度的增加而增大.采用罗丹明6G作为探针原子,6个Raman特征峰的平均增益值作为表征表面增强Raman散射衬底增益程度的量度.实验结果表明,Al₂O₃介质薄膜层的引入提高了纳米Ag颗粒的衬底介电常数,并引起了散射共振的增强,从而使表面增强Raman散射强度提高.     

梳状波导结构中石墨烯表面等离子体的传播性质

理论上研究了介质/石墨烯/介质梳状波导结构中表面等离子体的传播性质. 波导中表面等离子体模的有效折射率随着石墨烯费米能级的提高而减小, 随着介质折射率的增加而增加. 分析和仿真结果表明, 基于这种梳状波导可以在中红外波段实现新型的纳米等离子体滤波器, 器件的尺度在几百纳米的范围. 通过改变梳状分支的长度, 石墨烯的费米能级, 介质的折射率和波导中石墨烯的层数, 很容易来调节带隙的位置. 另外, 滤波带隙的宽度随着梳状分支数的增加而增加. 这种滤波性质将在可调的高集成光子滤波器件中具有潜在的应用.     

单层石墨烯水分子吸附对其光学性质的影响

用基于第一性原理中的密度泛函理论MS软件对水分子吸附在单层石墨烯表面进行计算,使用广义梯度近似和周期性平面模型,得到不同数量的水分子吸附在石墨烯表面上的吸附能,并且计算了相对应的光学性质.得到的结果是吸附能很小,主要是范德瓦尔斯相互作用.石墨烯具有高疏水性,水分子在石墨烯表面对石墨烯的电子结构几乎没有作用,吸附不同个数的水分子后对石墨烯的光学性质有一定影响,其中吸附单个水分子后变化并不明显,吸附2或3个水分子后吸收率和光电导率略有下降;折射率和消光率下降不明显,说明吸附水对石墨烯的透明度影响不大;介电函数的实数部分变化趋于平缓,虚数部分有明显下降;能量损失增加.     

单层石墨烯水分子吸附对其光学性质的影响

用MS软件对水分子吸附在单层石墨烯表面进行计算,采用第一性原理中的密度泛函理论。使用广义梯度近似和周期性平面模型,得到不同数量的水分子吸附在石墨烯表面上的吸附能,并且计算了相对应的光学性质。得到的结果是吸附能很小,主要是范德瓦尔斯相互作用。石墨烯具有高疏水性,水分子在石墨烯表面对石墨烯的电子结构几乎没有作用,吸附不同个数的水分子后对石墨烯的光学性质有一定影响,其中吸附单个水分子后变化并不明显,吸附2或3个水分子后吸收率和光电导率略有下降;折射率和消光率下降不明显,说明吸附水对石墨烯的透明度影响不大;介电函数的实数部分变化趋于平缓,虚数部分有明显下降;能量损失增加。     

Optical and structural parameters of the ZnO thin film grown by pulsed filtered cathodic vacuum arc deposition

Transparent conductive ZnO film was deposited on glass substrate by pulsed filtered cathodic vacuum arc deposition (PFCVAD). Optical parameters such as absorption coefficient α, the refractive index n, energy band gap E_g and dielectric constants have been determined using different methods. Kramers-Kronig and dispersion relations were employed to determine the complex refractive index and dielectric constants using reflection data in the ultraviolet-visible-near infrared regions. The spectra of the dielectric coefficient were used to calculate the energy band gap and the value was 3.24 eV. The experimental energy band gap was found to be 3.22 eV for 357 nm thick ZnO thin film. The envelope method was also used to calculate the refractive index and the data were consistent with K-K relation results. The structure of the film was analyzed with an x-ray diffractometer and the film was polycrystalline in nature with preferred (002) orientation.