Open Resonators with Conducting Cylindrical Inserts. 1. Two-Dimensional Model

We present the results of computer simulation of the properties of modes in a two-dimensional open resonator with a conducting cylindrical insert. An increase in the diffraction Q-factor of the fundamental mode by 2–3 orders of magnitude due to the conducting cylindrical insert is found and studied. The prospects of using this phenomenon for controlling the spectrum, frequencies, and Q-factors of excited modes are discussed. The tunability of the open resonator with a conducting cylindrical insert for one (fundamental) mode in a wide frequency range is shown. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 7, pp. 596–604, July 2005.     

Open Resonators with Conducting Cylindrical Inserts. 2. Resonators with Finite-Length Mirrors

We present the results of experimental studies of controlling the spectrum and Q-factors of modes in an open resonator with a conducting cylindrical insert. The phenomenon of an increase in the diffraction Q-factor is experimentally observed for the fundamental TEM_00q mode for two resonant diameters of the conducting cylindrical insert located inside the open resonator. The features of excitation of modes in an open resonator with smooth cylindrical finite-length mirrors and in an open resonator with cutoff bevels at the mirror edges are studied. Prospects for using open resonators with conducting inserts in quasi-optical devices in the millimeter-wave range are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 8, pp. 684–691, August 2005.     

Highly efficient design of spectrally engineered whispering-gallery-mode microlaser resonators

We present an accurate, reliable and versatile method for studying the effect of deformations on the characteristics of the high-Q whispering gallery (WG) modes supported by two-dimensional dielectric resonators (DR). An eigenvalue problem is formulated in terms of contour integral equations and further discretised with the method of analytical regularisation. Such a procedure significantly reduces the number of unknowns whilst providing high and controllable accuracy. Natural frequencies, Q-factors and field patterns of elliptical, flower- and egg-shaped DRs are calculated. Methods to enhance the Q-factors, provide directional light output, and parasitic mode suppression are discussed. The identification of WG modes is simplified by the symmetrical/asymmetrical mode separation included into the formulation of the problem and solution algorithm.     

The linrational modes of H2O molecule in solids

The librational modes of H₂O molecule have been critically discussed. Assuming a simple model for H₂O, equations have been developed to compute the force constants k_H and k_H which primarily determine the frequencies of the modes. It is inferred that these modes should be sensitive to H-bonding and insensitive to metal-oxygen coordination. It is also suggested that the unique assignments of rocking and wagging modes are possible if the nature of H-bonds exhibited by H₂O molecule is correctly known.     

Measurement of the photoconductivity of semiconductors at ultrahigh frequencies

Relations are derived which permit the absolute value of the photoconductivity of a semiconductor to be determined from UHF measurements. The cases considered include various placements of a sample within a cylindrical resonator for the H₀₁₁ and E₀₁₀ modes, and the H_01p modes in a rectangular resonator. The results derived are correct if we consider the random character of light absorption and neglect the diffusion of photo-excited carriers. Working formulas are given for calculating the design of a measuring setup with a re-entrant resonator. All conclusions are accurate in the small-perturbation approximation.     

Natural electromagnetic modes of a resonator formed by cutoff waveguides

A spectral three-dimensional problem is solved to determine the resonant frequencies of a branch formed by the orthogonal intersection of cutoff rectangular waveguides. Expressions for the H _mng and E _mng modes are derived and analyzed. Two classes of free nonradiating modes typical of this structure are identified and analyzed. Numerical calculations are made of the dispersion relations obtained for the different modes. Zh. Tekh. Fiz. 69, 84–88 (April 1999)     

椭圆手征波导的传输特性

首先给出了填充手征媒质的一般柱结构中耦合波方程的解耦过程,然后根据完备本征函数展开对椭圆手征波导中的混合模式进行了详细分析,给出具体的场表达式及色散关系.指出在与椭圆结构相关的耦合问题中,不仅存在TE与TM模式之间的耦合,还存在偶型模与奇型模式的耦合.通过数值计算对椭圆离心率以及手征导纳对色散特性的影响进行了讨论. 关键词： 椭圆手征波导 马丢函数 模式分裂     

Electrostrictive laser-induced gratings for time-resolved observation of translational-rotational energy transfer in H2

Electrostrictive laser-induced gratings (LIG) have been formed in H₂ of various pressures (0.5…5 bar) and with frequencies of the Brillouin modes (sound waves) of about 14 MHz. Under these conditions, the rotational degrees of freedom can only partially follow the temperature variation from the acoustic oscillation. A model is given, which completes the linearized fluid dynamical equations with equations for the rotational state relaxation, separately for the average relaxation of the states for Ortho-H₂ and Para-H₂. Using such a model, the dispersion of sound frequency is reproduced with an accuracy of a few percent. However, the total dissipation of sound and the observed strong alternation in peak heights in the temporal evolution of the LIG intensity is only approximately predicted by the model.     

非截面二维光子晶体排列矩形波导的全模式分析

在对周期性结构进行谐波分析的基础上，导出了非截面二维光子晶体排列矩形波导的本征值方程. 基于此方程，可以对该类光子晶体波导的所有可能模式进行分析. 分析认为，非截面二维光子晶体排列矩形波导内能存在的模式包括E_(y)，TE_y，H_(y)和TM_y模式；改变波导高度，可以实现E_(y)模式和H_(y)模式与其他模式通带的完全分离. 然而改变任一结构参数，都不能使E_(y)和H_(y)的各个模式通带，以及E_(y)1模式和H_(y)1模式的通带完全隔离. 波导单模工作的带宽由E_(y)1和E_(y)2模式的低端截止频率决定. 关键词： 波导 光子晶体 本征值方程 模式     

Free vibrations of laminated composite cylindrical shells with an interior rectangular plate

The free vibration analysis of a laminated composite cylindrical shell with an interior rectangular plate is performed by the analytical and experimental methods. The frequency equations of vibration of the shell including the plate are formulated by using the receptance method. To obtain the free vibration characteristics before the combination of two structures, the energy principle based on the classical plate theory and Love's thin shell theory is adopted. The numerical results are compared with the results from an experiment, as well as a finite element analysis, to validate the current formulation. The influences of the length-to-radius ratio (L_S/a) and radius-to-thickness ratio (a/h_S) of the shell and fiber orientation angles (Θ) of symmetric cross- and angle-ply composite materials on the natural frequencies of a cylindrical laminated combined shell are also discussed in details.     

Natural frequencies and modes of open cylindrical shells with a circumferential thickness taper

An analytical procedure to estimate not only the natural frequencies but also modes of open cylindrical shells with a circumferential thickness taper by the transfer matrix method is presented. The transfer matrix is derived from the non-linear differential equations for the cylindrical shells by numerical integration. The accuracy and convergence characteristics of this method are investigated, and the natural frequencies and modes of open cylindrical shells with a circumferential thickness taper are presented for various curvatures, aspect ratios, boundary conditions and thickness ratios. Furthermore, the influences of thickness variation of the cross-section on the natural frequencies and modes are examined.     

Self-consistent phonon treatment of second-order displacive ferroelectric

The high-temperature Curie-Weiss law of electric susceptibilityχ can be explained by quartic interactions between ak～ 0 optic mode, whose normal mode co-ordinateq ₀ is proportional to the polarization, and acoustic vibrations of the lattice. These interactions will either stabilize q₀ at low temperature, preventing a ferroelectric transition, or else such a transition will occur. To obtain coexisting paraelectric and ferroelectric phases at 0 °K, with distinctχ vs.T curves for each phase as observed bySaifi andCross in SrTiO₃, one must invoke anharmonic interactions between q₀ and low-lying, temperature-dependent optic modes. These interactions are treated by the self consistent phonon method, which introduces an effective harmonic HamiltonianH _h and calculates the Helmholtz functionF to first order inH-H_h. The approximation is optimized by minimizingF with respect to the renormalized optical mode frequencies appearing inH _h, for which a system of integral equations is obtained by the minimization procedure. The condition that there are enough low-lying optic modes to produce coexisting phases leads to a prediction of weak optic dispersion at 0 °K. Under these circumstances, the self-consistent phonon equations can be approximated by a pair of coupled cubic equations. From the solution of these, we conclude thatF has three minima at 0 °K in SrTiO₃, corresponding to paraelectric and two oppositely polarized ferroelectric states. 180° domain walls must be few in number and immobile under a field, except in the presence of a high dislocation concentration.     

TE modes in parallel cylindrical surface waveguides

Dispersion equations for TE and TM modes in width-limited waveguides formed by parallel cylindrical surfaces are derived in adiabatic approximation. It is shown that the dominant TE₀₁ mode is strongly localized in the waveguide center.     

Raman and IR spectra of new organic metals (ET)8[Hg4X12(C6H5Y)2] (X, Y=Cl, Br)

The Raman and IR reflectivity spectra of the new organic metals (ET)₈[Hg₄X₁₂(C₆H₅Y)₂] (X, Y=Cl, Br) based on the molecule bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET in abbreviated form) have been investigated. These metals differ from the previously studied compounds, particularly, in the type of ET molecular packing in the quasi-two-dimensional conducting layers. A high reflectivity and a plasma minimum observed in the IR reflectivity spectrum indicate the presence of quasi-free charge carriers (holes), as in other conducting ET salts. However, the A _g vibrational modes in the Raman spectrum are not activated in the IR spectrum, as is the case of conducting ET salts with other packing types. The Raman lines are assigned to the normal vibrations in the ET molecule, and their ionization shifts are determined. It is demonstrated that the frequencies of the most intense line ν₃(A _g) show a linear dependence on the cation charge, which is characteristic of different ET salts. No correlations are revealed between the ν₃(A _g) frequencies and the packing type. The strong background with a broad maximum at a Raman shift of about 3000 cm^?1 is observed in the Raman spectra upon excitation with the 2.54-and 2.41-eV lines of an Ar⁺ laser. The assumption is made that such a background can be associated with the scattering by one-particle and collective electronic excitations.     

Vibrational spectra and normal coordinate analysis of dihalogenated benzenes. II. Out-of-plane vibrations

Assignments of the out-of-plane fundamental modes for D₄-ortho, meta and para fluorochloro and fluorobromo benzenes are given. A normal coordinate analysis, employing the 94 observed frequencies of the H₄ and D₄ molecules is carried out to obtain a 16-parameter Valence Force Feld, with an average difference of ±1.2% between observed and calculated frequencies. Unique assignments are obtained in the spectra of D₄-compounds for several of the weak or overlapping bands assigned as fundamentals in the H₄-compounds.     

柱坐标系中截断光束的广义M2因子

推导出截断圆对称光束二阶矩的传输方程，它们与无截断光束的二阶矩满足相似的传输定律.因此，基于广义截断二阶矩方法，将直角坐标系中截断二维光束的二阶矩特征参数推广到柱坐标系中的截断圆对称光束，类似方法定义的广义M²因子（M²_G因子）是一个传输不变量.对理论的自洽性作了物理解释.推导出柱坐标系中截断超高斯光束的二阶矩参数和M²_G因子.对一些有意义的特殊情况作了讨论，并以数值计算例作了说明. 关键词： 光束描述 截断光束 圆对称性 广义截断二阶矩(GTSM) 2因子（M²_G因子）')" href="#">广义M²因子（M²_G因子）     

Eigenschaften der Lösungen der nichtlinearisierten Ginsburg-Landau-Gleichungen in Zylindersymmetrie

Solutions of the nonlinear Ginzburg-Landau equations in cylindrical symmetry have been computed for a type I superconductor. From these solutions the behaviour of a circular cylinder of infinite length in a magnetic field parallel to its axis has been deduced. For a series of values of the magnetic field solutions are given in two cases. The first case was calculated with the assumption of no fluxoid frozen in (fluxoid quantum number n=0), whereas in the second case a vortex with fluxoid quantum numbern=1 was assumed on the axis of the cylinder. For both series of solutions investigation of the thermodynamic stability was carried out. This and further thermodynamic considerations led to the result that in a gedankenexperiment the transition from the normal to the superconducting state and vice versa can be performed in a reversible manner. The expulsion of the magnetic field from the sample during the reversible transition to the superconducting state (Meissner-Effect) is also described by the solutions. Further results are the existence of a supercooled state down to a magnetic fieldH _c2=κ√2H_cb and of a superheated state up to a fieldH _c1>H _cb. The value ofH _c1 depends on the radius of the cylinder. If a condensation to the superconducting state takes place at a fieldH ₀ whereH _c2<H ₀<H _cb, condensation withn=0 seems to be preferred in comparison to that withn=1.     

Ohmic selection in open coaxial resonators: An experimental study

A study of ohmic selective properties of open coaxial cylindrical resonators has been conducted experimentally and compared with theory. The resonator consists of an inner cylinder made of silicon carbide symmetrically located inside an outer cylindrical, tube shaped waveguide. Several fundamental TE modes were identified over the range 9 to 17 GHz through measurements of the resonant frequencies and the associated quality factors. Mode discrimination is achieved both by exploring selective ohmic effects and examining the electrodynamical properties of the coaxial cylindrical waveguide. The effectiveness of a silicon carbide coaxial insert in providing ohmic mode selection is demonstrated in that the totalQ factors of TE _mp modes with radial indexp2 become well below the quality factors for surface TE _m1 modes. It has been verified that both structure and number of resonant modes are strongly dependent on the diameter and the resistivity of the coaxial insert.