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Table of contents

    20 October 2004, Volume 13 Issue 10 Previous issue    Next issue
    GENERAL
    Reduced-order observer of singular system with unknown inputs
    Wu Jian-Rong (吴健荣)
    Chinese Physics, 2004, 13 (10):  1591-1596.  DOI: 10.1088/1009-1963/13/10/001
    Abstract ( 982 )   PDF (148KB) ( 605 )  
    For the general discrete singular system with unknown inputs, a new reduced-order observer is designed. A numerical example is presented to illustrate the design algorithms.
    Electron behaviour in CH4/H2 gas mixture in electron-assisted chemical vapour deposition
    Dong Li-Fang (董丽芳), Ma Bo-Qin (马博琴), Wang Zhi-Jun (王志军)
    Chinese Physics, 2004, 13 (10):  1597-1600.  DOI: 10.1088/1009-1963/13/10/002
    Abstract ( 976 )   PDF (187KB) ( 393 )  
    The behaviour of electrons in CH$_{4}$/H$_{2}$ gas mixture in electron-assisted chemical vapour deposition of diamond is investigated using Monte Carlo simulation. The electron drift velocity in gas mixture is obtained over a wide range of E/P (the ratio of the electric field to gas pressure) from 1500 to 300000 (V/m kPa$^{-1}$). The electron energy distribution and average energy under different gas pressure (0.1-20kPa) and CH$_{4}$ concentration (0.5%-10.0%) are calculated. Their effects on the diamond growth are also discussed. It is believed that these results will be helpful to the selection of optimum experimental conditions for high quality diamond film deposition.
    Phase shift of the population oscillation and population trapping
    Zhang Xian-Zhou (张现周), Jiang Hong-Min (江红民), Rao Jian-Guo (饶建国), Li Bai-Wen (李白文)
    Chinese Physics, 2004, 13 (10):  1601-1605.  DOI: 10.1088/1009-1963/13/10/003
    Abstract ( 1206 )   PDF (215KB) ( 375 )  
    Using our recently developed time-dependent multilevel approach, we have calculated the phase shift of the population oscillation of the excited potassium atom in frequency-modulated fields when the modulation amplitude is suddenly changed. The numerical results are in good agreement with the measurements. A new way of realizing population trapping is suggested.
    The novel multi-solitary wave solution to the fifth-order KdV equation
    Zhang Yi (张翼), Chen Deng-Yuan (陈登远)
    Chinese Physics, 2004, 13 (10):  1606-1610.  DOI: 10.1088/1009-1963/13/10/004
    Abstract ( 1125 )   PDF (164KB) ( 472 )  
    By using Hirota's method, the novel multi-solitary wave solutions to the fifth-order KdV equation are obtained. Furthermore, various new solitary wave solutions are also derived by a reconstructed bilinear B?cklund transformation.
    Lie symmetries and non-Noether conserved quantities for Hamiltonian canonical equations
    Fu Jing-Li (傅景礼), Chen Li-Qun (陈立群), Xie Feng-Ping (谢凤萍)
    Chinese Physics, 2004, 13 (10):  1611-1614.  DOI: 10.1088/1009-1963/13/10/005
    Abstract ( 1098 )   PDF (157KB) ( 496 )  
    This paper focuses on studying Lie symmetries and non-Noether conserved quantities of Hamiltonian dynamical systems in phase space. Based on the infinitesimal transformations with respect to the generalized coordinates and generalized momenta, we obtain the determining equations and structure equation of the Lie symmetry for Hamiltonian dynamical systems. This work extends the research of non-Noether conserved quantity for Hamilton canonical equations, and leads directly to a new type of non-Noether conserved quantities of the systems. Finally, an example is given to illustrate these results.
    Lie symmetries and invariants of constrained Hamiltonian systems
    Liu Rong-Wan (刘荣万), Chen Li-Qun (陈立群)
    Chinese Physics, 2004, 13 (10):  1615-1619.  DOI: 10.1088/1009-1963/13/10/006
    Abstract ( 1204 )   PDF (151KB) ( 571 )  
    According to the theory of the invariance of ordinary differential equations under the infinitesimal transformations of group, the relations between Lie symmetries and invariants of the mechanical system with a singular Lagrangian are investigated in phase space. New dynamical equations of the system are given in canonical form and the determining equations of Lie symmetry transformations are derived. The proposition about the Lie symmetries and invariants are presented. An example is given to illustrate the application of the result in this paper.
    The Lie symmetrical non-Noether conserved quantity of holonomic Hamiltonian system
    Fang Jian-Hui (方建会), Liao Yong-Pan (廖永潘), Peng Yong (彭勇)
    Chinese Physics, 2004, 13 (10):  1620-1622.  DOI: 10.1088/1009-1963/13/10/007
    Abstract ( 1103 )   PDF (135KB) ( 953 )  
    In this paper, we study the Lie symmetrical non-Noether conserved quantity of a holonomic Hamiltonian system under the general infinitesimal transformations of groups. Firstly, we establish the determining equations of Lie symmetry of the system. Secondly, the Lie symmetrical non-Noether conserved quantity of the system is deduced. Finally, an example is given to illustrate the application of the result.
    Surface waves in a vertically excited circular cylindrical container
    Jian Yong-Jun (菅永军), E Xue-Quan (鄂学全), Zhang Jie (张杰), Meng Jun-Min (孟俊敏)
    Chinese Physics, 2004, 13 (10):  1623-1630.  DOI: 10.1088/1009-1963/13/10/008
    Abstract ( 1036 )   PDF (2647KB) ( 382 )  
    The nonlinear free surface amplitude equation, which has been derived from the inviscid fluid by solving the potential equation of water waves with a singular perturbation theory in a vertically oscillating rigid circular cylinder, is investigated successively in the fourth-order Runge-Kutta approach with an equivalent time-step. Computational results include the evolution of the amplitude with time, the characteristics of phase plane determined by the real and imaginary parts of the amplitude, the single-mode selection rules of the surface waves in different forced frequencies, contours of free surface displacement and corresponding three-dimensional evolution of surface waves, etc. In addition, the comparison of the surface wave modes is made between theoretical calculations and experimental measurements, and the results are reasonable although there are some differences in the forced frequency.
    Instability of the vertically forced surface wave in a circular cylindrical container
    Jian Yong-Jun (菅永军), E Xue-Quan (鄂学全)
    Chinese Physics, 2004, 13 (10):  1631-1638.  DOI: 10.1088/1009-1963/13/10/009
    Abstract ( 1254 )   PDF (448KB) ( 432 )  
    The nonlinear amplitude equation, which was derived by Jian Yongjun employing expansion of two-time scales in inviscid fluids in a vertically oscillating circular cylindrical vessel, is modified by introducing a damping term due to the viscous dissipation of this system. Instability of the surface wave is analysed and properties of the solutions of the modified equation are determined together with phase-plane trajectories. A necessary condition of forming a stable surface wave is obtained and unstable regions are illustrated. Research results show that the stable pattern of surface wave will not lose its stability to an infinitesimal disturbance.
    Using symbolic computation to construct travelling wave solutions to nonlinear partial differential equations
    Li Wei (李伟), Xie Fu-Ding (谢福鼎)
    Chinese Physics, 2004, 13 (10):  1639-1643.  DOI: 10.1088/1009-1963/13/10/010
    Abstract ( 1196 )   PDF (159KB) ( 622 )  
    Based upon the symbolic computation and the coupled projective Riccati equation, the tanh function method is further improved. As its applications, Wu-Zhang equation (which describes a (2+1)-dimensional dispersive long wave) and the (1+1)-dimensional dispersive long wave equation obtained from Wu-Zhang equation by scaling transformation and symmetry reduction are chosen to illustrate the validity of the proposed approach.
    Preparation of arbitrary n-particle d-dimensional superposition states using only single qubit operations and CNOT gates
    Wang Yan-Hui (王艳辉), Fang Mao-Fa (方卯发)
    Chinese Physics, 2004, 13 (10):  1644-1648.  DOI: 10.1088/1009-1963/13/10/011
    Abstract ( 984 )   PDF (169KB) ( 406 )  
    In this article, using only single qubit operation and a CNOT gate, we propose a scheme for creating arbitrary n-particle d-dimensional superposition states including entangled states and give the relevant circuits for realizing this scheme.
    Coherent Landau states with gauge invariance
    Tian Xu (田旭), Zhao Zhong-Yun (赵中云), Li Ming-Fa (黎明发)
    Chinese Physics, 2004, 13 (10):  1649-1651.  DOI: 10.1088/1009-1963/13/10/012
    Abstract ( 1116 )   PDF (126KB) ( 352 )  
    Coherent states for the Landau system (planar charged particle moving in a uniform magnetic field) are developed. It is convenient to use these states to describe the circular motion of the charged particle. The results obtained do not depend on gauges.
    A Mössbauer study of the magnetic coupling in iron phosphorous trisulfides
    Dai Yao-Dong (戴耀东), Wang Lin (王林), Yang Ya-Xin (杨亚新), He Yun (何云), Huang Hong-Bo (黄红波), Xia Yuan-Fu (夏元复)
    Chinese Physics, 2004, 13 (10):  1652-1656.  DOI: 10.1088/1009-1963/13/10/013
    Abstract ( 915 )   PDF (206KB) ( 535 )  
    The polycrystalline sample of layered compound FePS$_3$ has been investigated by using Mössbauer spectroscopy (12K to 300K), magnetic susceptibility measurements, x-ray diffraction and FTIR spectroscopy. The antiferromagnetic order exists below $T_{\rm N}$=120.5±1K. The Mössbauer spectra below $T_{\rm N}$ indicate that the magnetization axis is perpendicular to the layer of FePS$_3$, and the divalent iron cations are in their high spin configurations. By fitting the hyperfine field parameters near the Néel temperature, we obtain information on the nature of magnetic interactions in the material. The results show that the magnetic coupling can be treated by the two-dimensional Ising model, and it can be interpreted on the basis of a crystal-field effect.
    NUCLEAR PHYSICS
    Lattice-Boltzmann simulation of particle-laden flow over a backward-facing step
    Chen Sheng (陈胜), Shi Bao-Chang (施保昌), Liu Zhao-Hui (柳朝晖), He Zhu (贺铸), Guo Zhao-Li (郭照立), Zheng Chu-Guang (郑楚光)
    Chinese Physics, 2004, 13 (10):  1657-1664.  DOI: 10.1088/1009-1963/13/10/014
    Abstract ( 1051 )   PDF (298KB) ( 532 )  
    This paper deals with the numerical simulation of gas-solid two-phase flows in an Eulerian-Lagrangian scheme. The particle tracks are calculated using a recently developed exponential Lagrangian scheme, and the approach presently used for the computation of fluid phase is based on a modified Lattice-BGK model. Different from earlier publications, the present study employs a two-way coupling mechanism to handle the interactions between carrier phase and dispersed phase in the model. This new model is applicable to simulating gas-solid two-phase flows. For example, based on the scheme, we have recaptured some phenomena of planar laminar particle-laden flow over a backward-facing step in this research, and found a new interesting phenomenon.
    Lie algebraic analysis for the nonlinear transportof intense pulsed beams in electrostatics lenses
    Lü Jian-Qin (吕建钦), Li Jin-Hai (李金海)
    Chinese Physics, 2004, 13 (10):  1665-1668.  DOI: 10.1088/1009-1963/13/10/015
    Abstract ( 1000 )   PDF (157KB) ( 362 )  
    The Lie algebraic method is applied to the analysis of the nonlinear transport of an intense pulsed beam in cylindrically symmetrical electrostatic lenses, and particle orbits in a six-dimensional phase space ($x, p_x, y, p_y, \tau, p_{\tau}$) are obtained in the second order approximation. They can also be acquired in the third or higher order approximation if needed. In the analysis, we divide the electrostatic lenses into several segments. Each segment is considered as a uniform accelerating field, and each dividing point is treated as a thin lens. The particle distribution in a three-dimensional ellipsoid is of Gaussian type.
    ATOMIC AND MOLECULAR PHYSICS
    Absorption spectroscopy of cold caesium atoms confined in a magneto-optical trap
    Yan Shu-Bin (闫树斌), Liu Tao (刘涛), Geng Tao (耿涛), Zhang Tian-Cai (张天才), Peng Kun-Chi (彭堃墀), Wang Jun-Min (王军民)
    Chinese Physics, 2004, 13 (10):  1669-1673.  DOI: 10.1088/1009-1963/13/10/016
    Abstract ( 1634 )   PDF (202KB) ( 540 )  
    Absorption spectra of cold caesium atoms confined in a magneto-optical trap are measured around $D_2$ line at 852nm with a weak probe beam. Absorption reduction dip due to electromagnetically induced transparency (EIT) effect induced by the cooling/trapping field in a V-type three-level system and a gain peak near the cycling transition are clearly observed. Several mechanisms mixed with EIT effect in a normal V-type three-level system are briefly discussed. A simple theoretical analysis based on a dressed-state model is presented for interpretation of the absorption spectra.
    Preparation and spectral characterization of new Er3+-doped TeO2-B2O3-WO3-ZnO-ZnS glasses
    Wang Guo-Nian (汪国年), Zhang Jun-Jie (张军杰), Xu Shi-Qing (徐时清), Dai Shi-Xun (戴世勋), Hu Li-Li (胡丽丽), Jiang Zhong-Hong (姜中宏)
    Chinese Physics, 2004, 13 (10):  1674-1678.  DOI: 10.1088/1009-1963/13/10/017
    Abstract ( 1350 )   PDF (222KB) ( 506 )  
    Erbium-doped TeO$_2$-based oxysulfide glasses have been prepared in argon atmosphere in graphite crucibles. The results of thermal analysis and spectroscopic properties of Er$^{3+}$ have been studied in terms of sulfide influence. As a function of composition, we have measured principally the optical absorption, spontaneous emission, and lifetime of the materials. Judd-Ofelt theory was introduced to calculate bandwidth and emission cross-section of Er$^{3+}$. The results demonstrate that addition of sulfide in tellurite glasses results in broad emission spectra, with high emission cross-section, slightly low emission lifetime and a comparatively high thermal stability as pure oxide glasses.
    Transfer ionization of the isocharge sequence ion and Ar collisions
    Cai Xiao-Hong (蔡晓红), Yu De-Yang (于得洋), Cao Zhu-Rong (曹柱荣), Lu Rong-Chun (卢荣春), Yang Wei (杨威), Shao Cao-Jie (邵曹杰), Chen Xi-Meng (陈熙萌)
    Chinese Physics, 2004, 13 (10):  1679-1683.  DOI: 10.1088/1009-1963/13/10/018
    Abstract ( 1101 )   PDF (176KB) ( 481 )  
    The ratios of transfer ionization to single capture for isocharge C$^{q+}$, N$^{q+}$, O$^{q+}$, Ne$^{q+}$ ions on Ar atoms are measured by using position-sensitive and time-of-flight techniques. It is found that the ratio $R_{1}$ increases with nuclear charge $Z$ in a $q=4$ sequence, and the ratio $R_{1}$ sequences have the minimum values at $Z=7$ and $Z=8$ in $q=5$ and $q=6$ sequences, respectively, and the ratio $R_{1}$ decreases with the increase in the nuclear charge $Z$ in a $q=7$ sequence. The results may be explained within the frame of the statistical model. It may be concluded that the transfer ionization depends remarkably upon the electronic structure of the projectile. The projectiles used in this study have the same charge state and velocity, but different electronic structures. The dependence of the ratio $R_{1}$ on q is studied for Ne$^{q+}$-Ar collisions. The ratio $R_{1}$ is found to increase as q increases for Ne$^{q+}$-Ar collisions. The measured dependence of the ratio $R_{1}$ on q is compared with the calculation using the molecular Coulomb over-barrier model.
    Electron impact ionization of large krypton clusters
    Li Shao-Hui (李邵辉), Li Ru-Xin (李儒新), Ni Guo-Quan (倪国权), Xu Zhi-Zhan (徐至展)
    Chinese Physics, 2004, 13 (10):  1684-1688.  DOI: 10.1088/1009-1963/13/10/019
    Abstract ( 1172 )   PDF (201KB) ( 402 )  
    We show that the detection of ionization of very large van der Waals clusters in a pulsed jet or a beam can be realized by using a fast ion gauge. Rapid positive feedback electron impact ionization and fragmentation processes, which are initially ignited by electron impact ionization of the krypton clusters with the electron current of the ion gauge, result in the appearance of a progressional oscillation-like ion spectrum, or just of a single fast event under critical conditions. Each line in the spectrum represents a correlated explosion or avalanche ionization of the clusters. The phenomena have been analysed qualitatively along with a Rayleigh scattering experiment of the corresponding cluster jet.
    CLASSICAL AREAS OF PHENOMENOLOGY
    Oscillation conditions of cw simultaneous dual-wavelength Nd:YAG laser for transitions 4F3/2-4I9/2 and 4F3/2-4I11/2
    Li Ping-Xue (李平雪), Li De-Hua (李德华), Li Chun-Yong (李春勇), Zhang Zhi-Guo (张治国)
    Chinese Physics, 2004, 13 (10):  1689-1693.  DOI: 10.1088/1009-1963/13/10/020
    Abstract ( 1084 )   PDF (186KB) ( 425 )  
    The operating condition of a cw simultaneous dual-wavelength Nd:YAG laser for both $^4$F$_{3/2}$-$^4$I$_{9/2}$ (quasi-three-level system) and $^4$F$_{3/2}$-$^4$I$_{11/2}$(four-level system) transitions is studied. According to this condition, the cw simultaneous dual-wavelength at 1.06μm and 946 nm in Nd:YAG crystal has been realized experimentally through an adaptive coating design of the cavity mirrors. A total power output of 2.5W of the dual-wavelength at 946nm and 1.06μm has been achieved with an optical conversion efficiency 14.3%. The experimental results are in good agreement with the theoretical analysis.
    Nonlinear cascade-configuration multi-wave mixing scheme based on electromagnetically induced transparency
    Li Jia-Hua (李家华), Yang Wen-Xing (杨文星), Peng Ju-Cun (彭菊村)
    Chinese Physics, 2004, 13 (10):  1694-1699.  DOI: 10.1088/1009-1963/13/10/021
    Abstract ( 1088 )   PDF (229KB) ( 426 )  
    A nonlinear optical cascade-configuration multi-wave mixing (CCMWM) scheme is presented and analysed for the generation of coherent light in a six-level atomic system in the context of electromagnetically induced transparency (EIT). A detailed semi-classical study of the propagation of the generated mixing and probe fields is demonstrated. We show by numerical simulations that EIT is capable of suppressing linear and nonlinear photon absorption. The analytical dependence of the generated mixing field on the probe field and the respective detuning is also predicted. Such a nonlinear optical process can be used for generating coherent short-wavelength radiation.
    Preparation of multicomponent motional coherent and squeezed coherent states of a trapped ion
    Li Jia-Hua (李家华), Yang Wen-Xing (杨文星), Peng Ju-Cun (彭菊村)
    Chinese Physics, 2004, 13 (10):  1700-1706.  DOI: 10.1088/1009-1963/13/10/022
    Abstract ( 1067 )   PDF (188KB) ( 343 )  
    In this paper, we present a scheme for preparation of multicomponent motional coherent and squeezed coherent states of the quantized centre of mass of an ion trapped in a one-dimensional harmonic potential and driven by two travelling-wave laser beams tuned to the nth red and blue vibrational sidebands, respectively. In addition, our scheme also provides experimental possibility for quantum state engineering.
    Measurement of the decoherence of a mesoscopic superposition of motional states of a trapped ion
    Zheng Shi-Biao (郑仕标)
    Chinese Physics, 2004, 13 (10):  1707-1710.  DOI: 10.1088/1009-1963/13/10/023
    Abstract ( 1027 )   PDF (138KB) ( 421 )  
    We propose a scheme to observe the decoherence of a mesoscopic superposition of two coherent states in the motion of a trapped ion. In the scheme the ion is excited by two perpendicular lasers tuned to the ion transition. The decoherence is revealed by the decrease of the correlation between two successive measurements of the internal state of the ion after relevant laser-ion interaction.
    Effect of relaxation rate on population distribution, EIT and refraction in $\varLambda$ and V systems
    Sun Qing-Qing (孙庆青), Gu Ying (古英), Gong Qi-Huang (龚旗煌)
    Chinese Physics, 2004, 13 (10):  1711-1716.  DOI: 10.1088/1009-1963/13/10/024
    Abstract ( 1296 )   PDF (237KB) ( 418 )  
    In the three-level Λ-type and V-type systems, we find that the same pump-effect parameter $R(=\frac{2|V_c|^2\gamma}{(\omega_{ac}-\omega_c)^2+\gamma^2})$ determines the population distributions, while the probe field leads to population fluctuations near the absorption peaks. With the increasing of the relaxation rate $\gamma$, the population distributions are shifted and their fluctuation amplitudes decrease. At the same time the electromagnetically induced transparency window becomes a broadened absorption peak, and the dispersion at the zero probe detuning changes from positive to negative. Large population fluctuation and non-fluctuation observed in different systems are attributed to the different relaxation rates.
    Output power spectrum of a single-mode laser driven by coloured pump and quantum noises with coloured correlation
    Han Li-Bo (韩立波), Cao Li (曹力), Wu Da-Jin (吴大进)
    Chinese Physics, 2004, 13 (10):  1717-1721.  DOI: 10.1088/1009-1963/13/10/025
    Abstract ( 950 )   PDF (371KB) ( 407 )  
    By using the linear approximation method, the output power spectrum is calculated for a single-mode laser driven by coloured pump and quantum noises with coloured correlation. We have observed that the configuration of the output power spectrum is complicated: that is, it can be of single peak, two peaks or three peaks. The configurations of the power spectrum can be transformed from one into another by changing the cross-correlation time, the cross-correlation coefficient between the two noises, and pump noise intensity.
    Quantum interference effects on the probe amplification without and with inversion in a four-level system
    Zhang Bing (张冰), Xu Wei-Hua (徐卫华), Zhang Hui-Fang (张惠芳), Gao Jin-Yue (高锦岳)
    Chinese Physics, 2004, 13 (10):  1722-1727.  DOI: 10.1088/1009-1963/13/10/026
    Abstract ( 966 )   PDF (222KB) ( 408 )  
    A four-level system driven by two coherent fields is considered. It is shown that in the presence of an incoherent pump, the probe gain at a short wavelength can be achieved due to the quantum interference. Our density matrix calculation provides the conditions for probe amplification from different origins, including gain without population inversion on any state basis, gain with population inversion on the dressed-state basis, and gain with population inversion on the bare-state basis. Also, by controlling the Rabi frequency of the coupling field a total change from non-inversion to inversion can be achieved which does not depend on the intensity of the incoherent pump.
    Analysis of the laser performance of Tm3+: ZBLAN glass at 1.47μm wavelength
    Huang Li-Lei (黄莉蕾), Cao Guo-Xi (曹国熹), Zhang Lun (张伦), Luo Hong-Lei (罗宏雷)
    Chinese Physics, 2004, 13 (10):  1728-1732.  DOI: 10.1088/1009-1963/13/10/027
    Abstract ( 1128 )   PDF (143KB) ( 407 )  
    A formula for the threshold energy of a four-level-system laser in Tm$^{3+}$ doped fluoride glass is derived. The formula contains the parameters of the interaction between the ions and the up-conversion rate of the pump-light. It is discussed that the Tb$^{3+}$ ions and the up-conversion pump-light have an influence on the laser performance of Tm$^{3+}$ ions around 1.47μm wavelength. We draw the following two conclusions. (1) The laser threshold descends obviously due to the doping of Tb$^{3+}$ ions, but the descending gradually flattens out with the increase of the content of Tb$^{3+}$ ions. Its suitable content is (1-2)×10$^{20}$cm$^{-3}$. (2) When pump-lights both from the up-conversion and from the ground state excite simultaneously the single-doped Tm$^{3+}$ ions, the threshold energy can reduce and the output energy can increase. In this paper, the energy conversion efficiency from the up-conversion pump-light to the output energy of laser is estimated.
    Investigation of stimulated Brillouin scattering for broadband KrF laser
    Wang Xiao-Hui (王晓慧), Lü Zhi-Wei (吕志伟), Lin Dian-Yang (林殿阳), Wang Chao (王超), Zhao Xiao-Yan (赵晓彦), Tang Xiu-Zhang (汤秀章), Zhang Hai-Feng (张海峰), Shan Yu-Sheng (单玉生)
    Chinese Physics, 2004, 13 (10):  1733-1737.  DOI: 10.1088/1009-1963/13/10/028
    Abstract ( 1080 )   PDF (208KB) ( 527 )  
    Stimulated Brillouin scattering (SBS) numerical mode for broadband multimode KrF laser pump with optical breakdown has been built up in this paper. The basic premises of the model are that KrF spectrum is composed of a number of lines and SBS arises from these lines with coupling to some extent. The broadband SBS threshold strongly depends on pump bandwidth. SBS and optical breakdown occur nearly simultaneously when broadband SBS and breakdown have the same threshold. The decrease of saturation reflectivity for broadband pump radiation is explained with this model. Experimental results agree well with the model.
    Grey-grey incoherently coupled spatial soliton pairs in guest-host photorefractive polymers
    Hou Chun-Feng (侯春风), Yao Feng-Feng (姚凤凤), Zhou Zhong-Xiang (周忠祥), Pei Yan-Bo (裴延波), Sun Xiu-Dong (孙秀冬)
    Chinese Physics, 2004, 13 (10):  1738-1741.  DOI: 10.1088/1009-1963/13/10/029
    Abstract ( 940 )   PDF (173KB) ( 464 )  
    We show that incoherently coupled grey-grey spatial soliton pairs can be established in guest-host photorefractive polymers under steady-state conditions, provided that their carrier beams have the same polarization, wavelength, and are mutually incoherent. The properties of these soliton pairs, such as their width and polarization, are discussed in detail.
    Study of the surface and far fields of terahertz radiation generated by large-aperture photoconductive antennas
    Zhang Tong-Yi (张同意), Cao Jun-Cheng (曹俊成)
    Chinese Physics, 2004, 13 (10):  1742-1746.  DOI: 10.1088/1009-1963/13/10/030
    Abstract ( 1080 )   PDF (219KB) ( 632 )  
    We have studied analytically the temporal characteristics of terahertz radiation emitted from a biased large-aperture photoconductive antenna triggered by an ultrashort optical pulse. We have included the effects of the finite lifetime and transient mobility dynamics of photogenerated carriers in the analysis. Succinct explicit expressions are obtained for the emitted radiation in the surface field and in the far field. The dependence of the waveforms of the radiated field on the fluence and duration of triggering optical pulse, carrier relaxation time and carrier lifetime are discussed in detail using the obtained expressions.
    RT instability in cylindrical implosion of jelly ring
    Yang Li-Bing (杨礼兵), Liao Hai-Dong (廖海东), Sun Cheng-Wei (孙承纬), Ouyang Kai (欧阳凯), Li Jun (李军), Huang Xian-Bin (黄显宾)
    Chinese Physics, 2004, 13 (10):  1747-1752.  DOI: 10.1088/1009-1963/13/10/031
    Abstract ( 1086 )   PDF (1690KB) ( 423 )  
    The interfacial RT instability experiments on imploding jelly liners in cylindrically convergent geometry have been performed. The liner's instability growth was observed clearly with a high-speed framing camera. Jelly liners have different initial perturbation forms on their inner and outer interfaces, being either smooth or sinusoidal. The initial perturbations also have different magnitudes and spatial frequencies (for example, mode n=5, 10, 20). The experimental results show that the growth and coupling of perturbations on inner and outer surfaces are remarkably different. Meanwhile, the relevant 2-D numerical simulation of hydrodynamics combined with Level Set method has been performed. Using the numerical code, we can design the parameters of imploding jelly liner, and predict the experimental results. The results of simulation are demonstrated to be in good agreement with the measured data in a series of experiments.
    CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
    Raman spectra of ZnSe nanoparticles synthesized by thermal evaporation method
    An Hui-Zhi (安辉芝), Zhao Qing (赵清), Du Wei-Min (杜为民)
    Chinese Physics, 2004, 13 (10):  1753-1757.  DOI: 10.1088/1009-1963/13/10/032
    Abstract ( 1657 )   PDF (269KB) ( 508 )  
    ZnSe nanoparticles were synthesized by using a thermal evaporation method for a vapour phase reaction of zinc and selenium sources. The sample was characterized by XRD, TEM, HRTEM and Raman spectroscopy. Raman spectra of longitudinal-optical (LO) like mode was analysed by a macroscopic continuum dielectric model. Large broadening of LO-mode is homogeneous and comes from the relaxation of the phonons at the interface and contribution of defects. Surface modes give the main contribution to the asymmetry of the lineshape.
    Thermalization time of thin metal film heated by short pulse laser
    Xu Hong-Yu (徐红玉), Zhang Yuan-Chong (张元冲), Song Ya-Qin (宋亚勤), Chen Dian-Yun (陈殿云)
    Chinese Physics, 2004, 13 (10):  1758-1765.  DOI: 10.1088/1009-1963/13/10/033
    Abstract ( 1103 )   PDF (357KB) ( 487 )  
    Based on the hyperbolic two-step heat conduction model, using the Laplace transform and numerical inverse transform method (Riemann-sum approximation method), the thermal behaviour of thin metal films has been studied during femtosecond pulse laser heating. Also the thermalization time, which is the time for the electron gas and solid lattice to reach thermal balance, has been studied in detail. The values of thermalization time for silver (Ag), gold (Au), copper (Cu) and lead (Pb) are obtained. The effects of material parameters of the thin metal film on the thermalization time are considered for the four kinds of metals by changing one of the parameters and regarding the other parameters as constant. For a typical metal material, the order of the thermalization time is of the order of hundreds of picoseconds. The thermalization time decays exponentially with the increase of phonon-electron coupling factor or electron gas thermal conductivity, and it increases linearly with the increase of the ratio of lattice heat capacity to electron gas heat capacity. However, the relaxation time of the electron gas has very little effect on the thermalization time.
    CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
    Quantum fluctuation of mesoscopic distributed parameter circuits
    Luo Hai-Mei (罗海梅), Liu Gang (刘刚), Xu Lin (徐林), Ji Ying-Hua (嵇英华)
    Chinese Physics, 2004, 13 (10):  1766-1769.  DOI: 10.1088/1009-1963/13/10/034
    Abstract ( 1048 )   PDF (151KB) ( 338 )  
    Under the Born-von-Karmann periodic boundary condition, we propose a quantization scheme for a non-dissipative distributed parameter circuit (a uniform transmission line). Quantum fluctuations of charge and current in the vacuum state are investigated by adopting the canonical transformation and unitary transformation method. Our results indicate that in distributed parameter circuits, quantum fluctuations, which also have distributed properties, are related to both the circuit parameters and the positions and the mode of signals.
    GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
    Numerical solution of Helmholtz equation of barotropic atmosphere using wavelets
    Wang Ping (汪萍), Dai Xin-Gang (戴新刚)
    Chinese Physics, 2004, 13 (10):  1770-1776.  DOI: 10.1088/1009-1963/13/10/035
    Abstract ( 967 )   PDF (366KB) ( 383 )  
    The numerical solution of the Helmholtz equation for barotropic atmosphere is estimated by use of the wavelet-Galerkin method. The solution involves the decomposition of a circulant matrix consisting up of 2-term connection coefficients of wavelet scaling functions. Three matrix decompositions, i.e. fast Fourier transformation (FFT), Jacobian and QR decomposition methods, are tested numerically. The Jacobian method has the smallest matrix-reconstruction error with the best orthogonality while the FFT method causes the biggest errors. Numerical result reveals that the numerical solution of the equation is very sensitive to the decomposition methods, and the QR and Jacobian decomposition methods, whose errors are of the order of $10^{-3}$, much smaller than that with the FFT method, are more suitable to the numerical solution of the equation. With the two methods the solutions are also proved to have much higher accuracy than the iteration solution with the finite difference approximation. In addition, the wavelet numerical method is very useful for the solution of a climate model in low resolution. The solution accuracy of the equation may significantly increase with the order of Daubechies wavelet.
ISSN 1674-1056   CN 11-5639/O4
, Vol. 13, No. 10

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