含左手材料的——维“啁啾”光子晶体的偏振特性

把“啁啾”函数引入含左手材料的一维光子晶体中,且左手材料的介电常数和磁导率采用Lossy Dryde model,利用传输矩阵法研究了其透射谱.结果表明:在“啁啾”函数对材料几何厚度调制较小时,该光子晶体有完整的禁带,随着调制的加强,禁带宽度增加,但底部逐步抬高.在相同的调制下,磁、电等离子体频率的比值越大,禁带宽度越宽.入射角增加,TE模的禁带宽度不变而TM模的禁带宽度变窄,TE模和TM模均产生了角度隙,此角度隙的宽度随入射角增加而变宽,且TM模的变化大于TE模的.周期数N变化时,角度隙基本不变.nR的变化对禁带和角度隙的位置没有影响,但nR越小,禁带底部越高且圆,角度隙中透射峰峰值越大.     

各向异性圆柱光子晶体中光波的量子效应和带隙

利用光波在一维各向异性圆柱光子晶体中径向受限的条件,研究了光波在其中出现的模式量子效应,并利用特征矩阵法计算了TE波和TM波各模式的禁带随模式量子数、传播方向以及圆柱半径的变化规律.得出了一些一维各向异性圆柱光子晶体带隙的新结构.研究表明:此结构禁带的频率中心和透射角都随模式量子数的增加而增大.同一模式禁带的频率中心随圆柱半径的增加而减小.     

填充比对三角晶格等离子体光子晶体色散关系的影响

采用有限单元法,分别对TE模式、TM模式下三角晶格等离子体光子晶体的色散关系进行了理论计算,分析了等离子体填充比对能带位置和禁带宽度的影响.结果 表明:TM模式下等离子体光子晶体在M-F、X-M两个方向上存在不完全带隙,随填充比的增加,带隙位置向高频移动,禁带宽度增大直至达到一稳定值.TE模式下等离子体光子晶体不仅存在禁带结构,还在低频处形成了表面等离子体波的平带结构.随填充比的增大,TE模式等离子体光子晶体由X-M单一方向的不完全带隙形成了完全带隙,带隙宽度随填充比的增大而增大.本文提供了一种可调谐等离子体光子晶体的有效方法,有望应用于微波、THz波的可调性控制.     

In掺杂ZnO光学性质的第一性原理研究

采用线性缀加平面波的方法,对In元素掺杂ZnO电子结构和光学性质进行研究.计算结果表明:掺In后价带上部分折叠态增加,禁带宽度变窄.不同量In掺杂ZnO与未掺杂时相比,折射率、反射率及消光系数均有明显变化,介电函数虚部向高能量方向移动,而折射率、反射率、吸收系数、消光系数均向低能量方向移动.从理论上指出了光学性质和电子结构之间的联系.     

固-流结构声子晶体中弹性波能带的色散研究

推导出弹性波斜入射固-流结构声子晶体的转移矩阵和色散公式.利用色散公式研究了弹性波在固-流结构声子晶体中的能带特性.结果表明,介质厚度固定时,弹性波中会出现多级禁带,禁带的频率中心随入射角的增加而向高频方向移动,入射角增加到一定值后会分裂出新的禁带,分裂出的禁带频率宽度随级数的增加而增大.入射角固定时,禁带的频率宽度随介质厚度近似成反比变化,分裂出的禁带频率宽度随介质厚度的增加而减小.     

多孔氧化铝/氧化锌组装体的光子带隙和发光性能

从光子晶体的角度研究了AAO/ZnO组装体的光子带隙和发光性能,并解释了该组装体中ZnO发光增强的原因.利用平面波法对AAO及AAO/ZnO组装体的带隙结构进行了研究,得到了该组装体在可见光范围内TE波和TM波的不同的禁带结构特征,讨论了晶格常数、填充比及填充介质的介电常数对带隙结构和禁戒波长的影响,找到了使AAO/ZnO组装体产生与ZnO的缺陷发光峰匹配的完全光子禁带的条件.     

一维光子晶体全方向反射带的研究

设计了由SiO2和Te构成的一维光子晶体结构,对该结构的全向反射带特性进行分析。找到了TE和TM模的全向反射带范围,TE模的反射带在785 nm到1258 nm内变化,TM模的反射带在785 nm到1099 nm范围内变化。讨论了晶格常数,晶格周期对该全向反射带的影响。结果表明,TE模的全向反射带始终比TM模的宽。晶格常数增大,TE和TM模的全向反射带均向归一化频率较高(对应长波)的方向移动。晶体周期增大,TM模的全向反射带会变窄,而TE模的全向反射带变化不大。此外还发现,参数变化对TM模的反射带的影响明显大于对TE模的影响。     

近红外宽带全方向反射镜的设计

研究了一维光子晶体的全方向反射镜.用传输矩阵法分析了影响全反镜全方向反射带带宽和位置的因素.利用带隙展宽理论,构建异质结构光子晶体,设计得到了近红外宽带全反射镜.比较发现,Te/SiO2构成的一维异质结构全向带反射特性优于TiO2/SiO2构成的一维异质结构,该反射镜TE偏振波的全方向反射带分布在近红外波段1 001 ～ 2999 nm范围内,TM偏振波的全向反射带分布在1001 ～2323 nm波段范围内,获得的反射率高于98;,而薄膜层数只需要20层.     

太赫兹波在光子晶体波导中的带隙特性研究

为了得到太赫兹波在二维三角晶格光子晶体中的传播特性,研究了填充比、介电常数比、晶格常数三个主要因素对二维三角晶格完全禁带的影响.利用MATLAB软件分别优化计算得到填充比、介电常数比、晶格常数最大完全禁带,以及对应结构参数之间的关系.带隙随着填充比的变化而变化,而对于相同晶格结构,介电常数比越大,完全禁带宽度越大,晶格常数不同,禁带宽度也不同.光子晶体态密度的分布验证了存在光子带隙的范围.研究结果为太赫兹波器件的开发提供了理论依据.     

一维声子晶体的传输特性

推导出一维声子晶体的转移矩阵,研究了一维声子晶体的传输特性.得出:声波在一维声子晶体中传播时会出现一系列禁带,各级禁带的频率中心是等间隔的,各级禁带的频率宽度是相等的.相邻禁带的频率中心的间隔随介质的厚度成反比变化,禁带的频率宽度随介质的厚度成反比变化.禁带的频率宽度随两介质声阻抗的差值的减小而减小.     

Spectrum of natural electromagnetic waves in a periodic ferromagnet-dielectric structure

The specific features of propagation of natural TE waves in a periodic ferromagnet-dielectric structure are investigated in the following geometry: a bias magnetic field is parallel to the ferromagnet/dielectric interface and perpendicular to the wave propagation direction. The transformation matrix for the period of the structure, the dispersion relation, and the energy reflection coefficient are obtained for the case of normal incidence of a wave on a semi-infinite periodic medium by solving the boundary-value problem. It is shown that an external field can be used to control the spectrum and characteristics of reflected waves.     

Linear Optical Properties in Multilayers of Polydiacetylenes

Abstract

The linear optical properties in multilayers of polydiacetylenes (PDA) have been investigated by studying both the transmission/absorption coefficients and the waveguide properties of the thin PDA films (?5000 A). The PDA films were deposited one monolayer at a time by the Langmuir Blodgett technique. The waveguide modes of the PDA waveguide (in an air - PDA film - silver configuration) were coupled via a grating at the air-PDA and/or PDA-Ag interface. Since the diacetylene chains are parallel to the interface, the TE wave/ waveguide modes (i.e., the electronic field is parallel to the PDA film), the system can be treated simply as an isotropic case. For TM wave/waveguide modes, the system has to be treated as an anisotropic one. The results of wavelength dependent linear optical property of PDA films and their impact to the waveguide properties as well as the grating coupling effects in the waveguide system will be discussed.     

固-固结构声子晶体中弹性波的禁带及其转型

引入四维波矢的概念,推导出弹性波斜入射固-固结构声子晶体的转移矩阵以及透射系数公式.利用这些公式计算了纵波和横波斜入射固-固结构声子晶体时纵波和横波的透射系数.结果表明:当纵波斜入射时,在透射波中纵波会出现禁带,并且也出现了纵波向横波的转型,随着入射角的增大转型越明显.当横波斜入射时也会出现类似于纵波斜入射时的现象.这些公式成功地解决了弹性波斜入射固-固结构声子晶体的传输问题和转型问题.     

An analytical model for combined radiative and conductive heat transfer in fiber-loaded silica aerogels

An improved analytical model for the total thermal conductivity of fiber-loaded silica aerogels was developed based on the complex refractive index, size, orientation, volume fraction and morphology of the fibers and silica aerogel. A cubic array of spherical porous secondary nanoparticles and a modified parallel-series model were proposed to model the combined solid and gaseous thermal conductivities. An anomalous diffraction theory (ADT) was used to predict the fiber extinction coefficient. Five common fiber types in the composites were studied including amorphous SiO₂ glass, silicon glass, common float glass, soda lime silica glass and borosilicate glass. The results show that the total extinction coefficient of the silica aerogel system is largest by loading with the common float glass fiber and lowest by loading with the soda lime silica glass among the five fiber types. The model provides theoretic guidelines for material designs with optimum parameters, such as the type, inclination angle, volume fraction and diameter of the fibers as well as the aerogel nanoparticle and pore sizes. The optimum fiber for improved thermal insulation should have a large spectral complex refractive index throughout the infrared region.     

Polariton spectrum of a bounded antiferromagnet with a center of antisymmetry in an external electric field oriented normally to the surface

The features of transmission of TE and TM polaritons through an interface between magnetic and nonmagnetic media and their localization at the interface in an external dc electric field have been studied. This field is directed along the hard magnetization axis. The magnetic medium is an easy-plane tetragonal antiferromagnet; it is odd with respect to inversion. A magnetic plate and a 1D magnetic photonic crystal in an external dc electric field, oriented normally to the interface, are considered.     

Thiol-ene/hyperbranched polymer hybrid thin films: Cure behavior and gas barrier properties

In this work, novel thiol-ene (TE)/hyperbranched polymer(HBP) hybrid thin films have been prepared by a simple photopolymerization method and the TE/HBP system was also investigated in terms of thermocuring behavior and gas barrier properties. The effect of added HBP on thermal curing (cross-linking) of TE polymer was examined with dynamic and isothermal differential scanning calorimeter (DSC) and compared with photocuring reaction of identical system. The structure of prepared TE/HBP hybrid thin film was analyzed by X-ray diffraction (XRD). Themomechanical analysis (TMA) provided extensive data on the coefficient of linear thermal expansion (CTE), dimensional change upon heating, and isothermal profile of TE/HBP hybrid thin films. Light transmittance as well as water/oxygen permeability of the resulting TE/HBP hybrid thin film was also measured depending on the HBP content.     

X-ray diffraction pattern of a Gulyaev-Bleustein surface acoustic wave in grazing geometry

The X ray diffraction pattern of a Gulyaev-Bleustein surface acoustic wave (SAW) under grazing angles of incidence in noncoplanar symmetric Laue geometry has been considered. It is supposed that the propagation direction of an SAW makes a small angle with the diffraction vector. It is shown that small deviations from the Bragg angle (～0.01″ induced by the SAW and do not affect the reflection coefficient lead to the formation of diffraction satellites both in the cases of standing and traveling SAWs. It has been established that the recorded diffraction pattern, which is a time-averaged intensity distribution, has characteristic profiles for odd and even satellites.     

Optical investigations of germanium nanoclusters – Rich SiO2 layers produced by ion beam synthesis

In this work, refractive index and extinction coefficient spectra of germanium nanoclusters – rich SiO₂ layers have been determined using variable angle spectroscopic ellipsometry (VASE) in the 250–1000 nm range. The samples were produced by Ge⁺ ion implantation into SiO₂ layers on Si substrates and subsequent annealing at temperatures from 700 to 1100 °C. It is known from previous investigations of similar samples that the Ge nanoclusterization process starts already at 800 °C and spherical Ge nanocrystallites 5–8 nm in diameter are observed in the SiO₂ layers after annealing for 1 h at even higher temperatures of 1000–1100 °C. Rutherford backscattering spectrometry (RBS) was employed to measure the Ge atom concentration depth profiles in the studied samples. The RBS results helped us choose realistic models for the VASE analysis which were necessary for a proper interpretation of the VASE data. It has been found that the refraction index value for the SiO₂/Si layer increases after Ge implantation. This effect can be explained by a defect-dependent compaction of ion-bombarded layers. A band’s tail in the extinction coefficient spectra for all the samples is observed which originates from a strong ultraviolet absorption band at 6.8 eV due to a Germanium Oxygen-Deficiency Center (GeODC) and/or a Ge-E’center in SiO₂. The annealing process results in the emergence of weaker extinction coefficient bands in the 400–600 nm region, associated with direct band-to-band transitions in Ge nanostructures. Transformation of these bands, including their blue-shift with the increasing annealing temperature could be explained via a quantum-confinement mechanism, by size and structural changes in Ge nanostructures.     

On the estimation of X-ray extinction changes due to randomly distributed dislocations in crystals

A procedure proposed by Ivanov, Klimanek and Skakov for the quantitative estimation of X-ray extinction in crystals containing randomly distributed dislocations is established without restriction concerning the defect density on the basis of stochastic geometry. The dependence of the extinction coefficient of a X-ray diffraction peak obtained in this way agrees very well with experimental observations.     

The features of identifying lines in a diffraction image formed by a widely divergent X-ray beam

A method for identifying lines in a diffraction image formed by a widely divergent X-ray beam and a technique for measuring the crystal structure parameters in the case of asymmetric crystal position have been developed. It is established that, once the distances between a crystal and a photographic plate and between the points of intersection of the hyperbola branches in a diffraction image are known, one can determine the angle between the crystal’s zone axis and the wave vector, which leads to multiwave diffraction. Relations linking this angle with the parameters of two atomic planes are obtained. It is found that, to measure the parameters of atomic planes belonging to a given zone, one can use different sets of crossed hyperbolas formed by radiations K _α and K _β. The measurements and calculations performed for the same sample (Si crystal), mounted symmetrically and asymmetrically, confirm the reliability of the proposed method.