基于气流调制的封闭空间高声强次声产生方法研究

基于气流调制技术研究了封闭空间高强度次声产生方法。设计了大流量气流调制器,对调制器和赫尔姆霍兹共振腔组成的高声强次声产生装置的声场特性进行了数值仿真,制作出原理装置,并进行了实验测试。从理论上分析了不同调制频率和不同供气压力下调制器出口的声压幅度,分析了次声产生装置不同调制频率的声压幅度,分析了舱内声场的空间分布特性。实验结果表明:气流调制器设计合理、运行平稳,次声产生装置最大能产生161 dB的次声,测试舱声场均匀、声波信噪比较高,实验结果与数值仿真结果基本一致。      

基于单通道反射型电光调制器实现不同路光同时调制的方法

提出了一种利用单通道反射型聚合物电光调制器同时调制不同路光的方法。衰减全反射结构的电光调制器,其每一个衰减全反射(ATR)峰的位置分别对应于一个导波共振模式。实验系统中利用衰减全反射导膜峰作为调制通道,使其每一路光路的入射角分别对应于不同导波共振模式的工作角,就可以实现利用单通道的电光调制器同时调制不同路光。提出了三种实现两路光同时调制的模式,并给出了三种模式的调制结果。结果表明,作为调制通道的导模阶数越低,调制效率越高。在832 nm光波波长下,采用最低阶导模进行调制时可以获得42.9%的调制效率。     

硅(111)面表面振动模

本文采用硅(111)面组成的平板结构模型,利用解动力学矩阵的方法,计算了不同层数体系的所有振动模。考虑到晶格弛豫后,该体系才可能存在表面模。由于表面模的激活,解释了Okada关于微晶硅的Raman峰向低波数大幅度移动的现象。同时利用杂化轨道理论计算了由于晶格弛豫引起的表面弹性常数的变化,从而得到表面模的频率为469cm^-1与实验中报道的硅的表面模频率430cm^-1接近。 关键词：     

电光调制器的温度特性及其最优化设计

利用线性电光效应的波耦合理论对铌酸锂晶体电光调制器的温度特性进行研究,给出了不同光波波矢和晶体光轴夹角情况下电光效应的温度变化特性,发现可以利用角度调节来克服电光调制器的温度敏感性;在此基础上,进一步对电光调制器进行了最优化设计,得到一个半波电压小(几十伏)、零场泄漏几乎为零(零电压出射光强和入射光强比为0．0027)、消光比达到365．6、温度性能稳定而且不需要透明电极的一个设计。     

Guide/antiguide optical intensity modulator

An electrorefractive index-controllable guide/antiguide optical intensity modulator has been created and characterized. The operating mechanism, beam propagation method simulation, device design and fabrication, and calculated and experimental results of this guide/antiguide modulator are given. The operational principle of the modulator is based on the field-induced waveguide (FIG) concept; that is, electric-field-induced refractive index changes cause the waveguide to be turned on and off electrically. The modulator is formed with a central narrow FIG electrode sandwiched between two antiguide electrodes. The electrooptic effects, along with carrier effects, have been exploited to adjust the refractive index under the guide and adjacent antiguide electrodes by changing reverse biases applied to them. The modulation is determined mainly by changing the lateral refractive index profiles. In the on state, a waveguide is formed under the central electrode, and the input light propagates along this waveguide. To realize the best off state, an antiguide situation is created that causes the light to diffract out of the central guide rapidly. An on/off ratio larger than 23 dB, a propagation loss 1 dB, and a record optical bandwidth from 1.0 to 1.55 m have been obtained for this modulator.     

The Investigation of Plasmon-Longitudinal Optical Phonon Coupling and Surface Polariton Modes in Donor Doped GaAs-Al0.33Ga0.67As Multi Quantum Wells

Infrared Fourier transform spectroscopy has been used to investigate phonon, plasmon, surface polariton and plasma-longitudinal optical phonon coupling in highly donor doped multi quantum wells (GaAs/Al_0.33Ga_0.67As) and direct band gap n- type Al_XGa_1-XAs thin layer on GaAs substrate. Using different samples with different concentration of free carriers. The dispersion equation of coupling modes have been calculated by using the condition which the dielectric functions of samples are zero for longitudinal coupled modes and experimental papameters which have been obtained from the best fit p-polarized oblique incidence far infrared reflection spectra. In MQW samples, the free carriers confined to the well and carriers are quasi two dimensional. So, plasmon- LO phonon coupling occur in the well (GaAs). In n- type Al_XGa_1-XAs thin layer, the coupled modes consist of three branches of the high, intermediate and low frequency modes. Their frequencies depend on both concentration and alloy composition. To analyses the surface polariton modes we carry out attenuated total reflection (ATR) measurements. In order to support our assignment the magnetic field profiles and surface polariton dispersion curves have been calculated.     

微纳光纤环形腔海水温度的谐振光谱分析

微纳光纤环形腔作为传感器件,具有灵敏度高、响应快的优点,因而越来越广泛地应用在传感领域。环形腔的谐振光谱直接反映外界环境的变化,因此谐振光谱分析对探测环境参数至关重要。从理论和实验研究了微纳光纤环形腔谐振光谱与海水温度的关系。首先,数值计算了基模(HE₁₁)两个垂直偏振态的传播常数随光纤直径和探测波长的变化关系,计算结果表明传播常数随光纤直径增大而增大,随波长增大而减小,同时计算了传播常数随海水温度的变化,海水温度越高,传播常数越大,表明海水温度的变化会影响到模式的传播常数,因而可以通过测量谐振光谱的变化得知海水温度的变化。其次,搭建了海水温度传感实验系统,获得了微纳光纤环形腔海水温度的谐振光谱,实验发现同时存在两套谐振峰,分别对应基模的TE模和TM模,两个偏振模式的传感灵敏度分别为5.54和5.24 pm·℃-1。最后,探讨了基模两个偏振态谐振光谱的产生原因,由于结型耦合区的扭曲耦合使得两个偏振态分离,并对两个偏振模式的谐振强度进行了分析。两个模式的谐振强度不同,而且随着波长的增加,一个模的谐振强度不断增强,另一个模的谐振强度逐渐减弱。这是由于不同耦合态的耦合系数和衰减决定的,而且他们随着波长而改变。实验结果与理论计算相吻合。     

Computation of collective excitations and elastic constants of expanded trigonal tellurium

The potential function derived from experimental structure factor data gives a repulsive minimum and also an attractive minimum. These two minima correspond to the first and second nearest-neighbour distances. Similar results have been obtained through the use of Percus-Yevick (PY) and hyper-netted chain (HNC) equations. The Hafner molecular dynamics results also show a similar trend. The first, second and third derivatives of the potential function have been obtained from the expression of the potential function. The first and second derivatives have been used to compute the phonon frequencies using Bhatia and Singh's (BS) method. The phonon frequencies obtained from Hubbard and Beeby's (HB) method show similar results. The elastic constants have also been calculated and the values obtained for C₁₁ by different methods are in good agreement. The Grüneisen constant has been calculated by two different methods which are in very good agreement with each other. From the Grüneisen constant the pressure derivative of the diffusion coefficient has been obtained and has been compared with that of Swalin's equation. The results are in excellent agreement with each other.     

Local and gap modes due to a substitutional impurity in alkali halides: One dimensional treatment

Local modes for substitutional impurity H in NaCl, NaBr and KCl have been calculated. Isotope shift for ³⁵Cl and ³⁷Cl substituted in KI has also been calculated. Good agreement with the experimental data has been obtained.     

Phonon dispersion in aluminium arsenide and antimonide

The phonon dispersion curves for aluminium arsenide and antimonide have been investigated by using a deformation bond approximation model. The results obtained from this model are compared with the experimental values wherever it is available. Since there is no complete experimental phonon dispersion curves for AlAs, we could not compare our calculated results, but the results of AlSb have been compared with the inelastic neutron scattering measurements at 15 K. However, we compare the phonon frequencies of AlAs and AlSb at critical points of the Brillouin zone obtained by our calculations and Raman spectroscopy measurements. This model predicts the phonon modes satisfactorily in all the symmetry directions of the Brillouin zone (BZ). The spectrum has similar features as observed in other III–V compound semiconductors.     

胞嘧啶分子拉曼光谱研究

本文通过实验测量了胞嘧啶的常规拉曼光谱,有四个弱拉曼峰在以前胞嘧啶的常规拉曼光谱中未检测到。采用密度泛函(Density Function Theory)B3LYP/6-31+G(d,p)计算了胞嘧啶分子的拉曼光谱。结合理论计算结果对实验拉曼光谱振动模式进行了指认,并对其中几个拉曼峰非常弱的原因进行了分析。     

Modeling and simulating of V-shaped piezoelectric micro-cantilevers using MCS theory considering the various surface geometries

Atomic force microscopy (AFM) is widely used as a tool in studying surfaces and mechanical properties of materials at nanoscale. This paper deals with mechanical and vibration analysis of AFM vibration in the non-contact and tapping modes for V-shaped piezoelectric micro-cantilever (MC) with geometric discontinuities and cross section variation in the air ambient. In the vibration analysis, Euler-Bernoulli beam theory based on modified couple stress (MCS) theory has been used. The governing equation of motion has been derived by using Hamilton's principle. By adopting finite element method (FEM), the MC differential equation has been solved. Damping matrix was considered in the modal space. Frequency response was obtained by using Laplace transform, and it has been compared with experimental results. Newmark algorithm has been used based on constant average acceleration to analyze time response of MC, and then time response results in the vibration mode, far from the sample surface have been compared with experimental data. In vicinity of sample surface, MC is influenced by various nonlinear forces between the probe tip and sample surface, including van der Waals, contact, and capillary forces. Time response was examined at different distances between MC base and sample surface, and the best distance was selected for topography. Topography results of different types of roughness showed that piezoelectric MC has been improved in the air ambient. Topography showed more accurate forms of roughness, when MC passes through sample surface at higher frequencies. The surface topography investigation for tapping and non-contact modes showed that using of these two modes are suitable for topography.     

Vibrational Dynamics of Poly(l-asparagine)

The normal modes and their dispersions for poly(l-asparagine) (PLN) in the α-helical form have been obtained in a reduced zone scheme with Wilson's GF matrix method as modified by Higgs. The results indicate that the modes below 1350 cm^?1 show appreciable dispersion. Optically active frequencies corresponding to the zone center and zone boundary are identified and discussed. Some of the characteristic features of the dispersion curves are repulsion accompanied by an exchange of character and von Hove singularities. Amide modes, side chain modes, and mixed modes are reported. The heat capacity calculated from the dispersion curves via density-of-states using Debye's relation is compared with the experimental data in the temperature range of 220–390 K.     

Deformation parameter changes in fission mass yields within the systematic statistical scission-point model

The fission fragment mass-yields are evaluated for pre-actinide and actinide isotopes using a systematic statistical scission point model. The total potential energy of the fissioning systems at the scission point is presented in approximate relations as functions of mass numbers,deformation parameters and the temperature of complementary fission fragments. The collective temperature, Tcoll, and the temperature of fission fragments, Ti, are separated and the effect of collective temperature on mass yields results is investigated. The fragment temperature has been calculated with the generalized superfluid model. The sum of deformation parameters of complementary fission fragments has been obtained by fitting the calculated results with the experimental data. To investigate the transitions between symmetric and asymmetric modes mass yields for pre-actinide and heavy actinides are calculated with this model. The transition from asymmetric to symmetric fission is well reproduced using this systematic statistical scission point model. The calculated results are in good agreement with the experimental data with Tcoll= 2 Me V at intermediate excitation energy and with T_(coll)= 1MeV for spontaneous fission.Despite the Langevin model, in the scission point model, a constraint on the deformation parameters of fission fragments has little effect on the results of the mass yield.     

Coupled mode analysis of light modulation in dielectric waveguides

A detailed analysis of electrooptic light modulation in optical waveguides is presented. Several important problems of a waveguide modulator, such as the difference of waveguide axes from crystalline electrooptic ones, the distribution of transverse and longitudinal field components of light modes, and the traveling-wave property of the modulating field, are discussed. The analysis is based on the coupled mode theory, regarding the modulation as the coupling among sidebands of unperturbed waveguide modes. The coupled mode equation is derived for the modulation in optical waveguides. It can be solved if the normal modes of the waveguide are given. Actually the equation is solved for the modulation in dielectric slab waveguides and the mechanism of modulation is discussed. The results of the analysis are applied to designing two types of waveguide modulators. In an example (10.6 μm modulator with a GaAs slab waveguide) a new efficient crystal orientation is found. The calculated phase retardation with this orientation is 0.13 rad/(V·cm) with a 1 μm thick slab. Another example of a 0.633 μm modulator using a LiTaO₃ crystal as a substrate is also described.     

Concentration‐dependent surface‐enhanced Raman scattering and molecular dynamic study of dimethyl formamide

A concentration‐dependent Raman study of dimethyl formamide (DMF) in Ag nanocolloidal solution was carried out in order to observe the effect of concentration on the surface enhancement mechanism. The Raman spectra in the region 900–2200 cm⁻¹ comprising four prominent Raman modes were measured experimentally and analyzed at five different concentrations: 1, 3, 5, 7, 10 mM , and in neat DMF. In order to find the possible configurations of DMF + Ag complexes, density functional theory (DFT) calculations were carried out taking one, three and five Ag atom clusters. The Raman spectra of unconjugated DMF, DMF + Ag and DMF + 3Ag complexes were calculated theoretically to assign the vibrational modes under consideration more accurately and to understand the wavenumber shift and change in intensity observed in experimental measurements. Water present in the colloidal solution may also conjugate with DMF and its complexes with Ag. In order to see the influence of water on the wavenumber shift and intensity changes, we have also obtained the optimized structures and Raman modes of DMF + water and DMF + water + Ag complexes. Good agreement between the experimental and theoretical wavenumber shifts has been obtained by using B3LYP functional theory and CEP‐31G basis set for the DMF + Ag complex. The experimental results suggest that the SERS enhancement is concentration‐dependent. The concentration‐dependent linewidth shows the existence of the phenomena of motional narrowing and diffusion dynamics in the colloidal solution. Copyright © 2007 John Wiley & Sons, Ltd.     

非简并光学参量振荡腔的经典增益

采用双晶体串接,温度调谐及光楔补偿方法,实现了参量振荡腔内泵浦场与非简并亚谐波场之间的三模同时共振,测定了系统的经典增益,实验结果与半径典理论计算符合.     

Study of Vibronic Spectra of Tetrabenzoporphin Based on Normal-Coordinate Analysis

The quasi-line fluorescence spectra have been measured and analyzed in detail for the molecules of tetrabenzoporphin and its N-deuterated derivative in n-octane. The calculations of the normal modes of these molecules have been carried out with the use of the valence force fields of porphin and phenanthrene. Sufficiently good agreement of the calculated and experimental frequencies of the modes has been obtained without variation of the force constants. Detailed interpretation of the fluorescence spectra is given.     

Resonant magnetopolaron effects in GaAs/AlGaAs multiple quantum well structures

A detailed experimental study of electron cyclotron resonance (CR) has been carried out at 4.2 K in three modulation-doped GaAs/Al_0.3Ga_0.7As multiple quantum well samples in fields up to 30 T. A strong avoided-level-crossing splitting of the CR energies due to resonant magnetopolaron effects is observed for all samples near the GaAs reststrahlen region. Resonant splittings in the region of AlAs-like interface phonon modes of the barriers are observed in two samples with narrower well width and smaller doping concentration. The interaction between electrons and the AlAs interface optical phonon modes has been calculated for our specific sample structures in the framework of the memory-function formalism. The calculated results are in good agreement with the experimental results, which confirms our assignment of the observed splitting near the AlAs-like phonon region is due to the resonant magnetopolaron interaction of electrons in the wells with AlAs-like interface phonons.     

Energy loss straggling of fast charged particles

Energy loss straggling of fast charged particles colliding with atoms have been considered in the eikonal approximation. The result is represented in the form of the Fano formula with a nonperturbative correction. The known nonperturbative Titeica formula (which is transformed to the Fano formula when perturbation theory is applicable) is obtained only under certain approximations in eikonal calculations. It has been shown that straggling calculated with allowance for nonperturbative effects at large charges of the projectile can be significantly different (by an order of magnitude) from the results obtained by Titeica, Fano, and Bohr. Energy loss straggling of fast highly charged ions on hydrogen and copper atoms have been calculated. The latter results are compared to experimental data.