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Volume 21 Issue 2
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Original Articles
Symmetries and Strong Symmetries of the (3+1)-Dimensional Burgers Equation
LIAN Zeng-Ju, LOU Sen-Yue,
Chin. Phys. Lett. 2004, 21 (2): 219-222 .  
Abstract   PDF(pc) (208KB) ( 541 )
The strong symmetries (recursion operators) and the inverse strong symmetries of a (3+1)-dimensional Burgers equation are given explicitly. Infinitely many symmetries of the considered model are obtained by acting the strong symmetries and the inverse strong symmetries on some seeds. An infinite-dimensional full Lie point symmetry algebra is also given.
Infinite-Parameter Potential Symmetries and a New Exact Solution for the Particle-Cluster Dynamic Equation
ZHANG Shan-Qing, LI Zhi-Bin
Chin. Phys. Lett. 2004, 21 (2): 223-226 .  
Abstract   PDF(pc) (201KB) ( 357 )
The master equation of a one-dimensional lattice-gas model with order preservation where the occupation probabilities of sites corresponding to Bose statistics as a consequence of the prescribed dynamics is studied with the potential symmetry method. The infinite-parameter potential symmetry and a new exact solution are obtained. The result illustrates that there remains the possibility of the above nonlinear equation to a linear partial differential equation by a non-invertible mapping.

Stabilizing Unstable Equilibrium Point of Unified Chaotic Systems with Unknown Parameter Using Sliding Mode Control
GUAN Xin-Ping, HE Yan-Hui
Chin. Phys. Lett. 2004, 21 (2): 227-229 .  
Abstract   PDF(pc) (390KB) ( 762 )
The control problem of a unified chaos is considered. Stabilizing unstable equilibrium point is achieved by a sliding mode controller based on parameter identification. The observer is applied to identify the unknown parameter of a unified chaotic system. Simulations are made and the results verify the validity of the proposed method.
Behaviour of Cubic Nonlinear Schrödinger Equation by Using the Symplectic Method
LIU Xue-Shen, DING Pei-Zhu
Chin. Phys. Lett. 2004, 21 (2): 230-232 .  
Abstract   PDF(pc) (332KB) ( 409 )
The dynamic properties of cubic nonlinear Schrödinger equation are investigated numerically by using the symplectic method. We show that the trajectories in phase space will exhibit different behaviour (elliptic orbit or homoclinic orbit) with the increase of nonlinear perturbation. We illustrate this phenomenon by mean of linearized stability analysis. The theoretical analysis is consistent with the numerical results.

A High-Order Meshless Bhatnagar-Gross-Krook Scheme Based on Point Collocation
SUN Xi-Ming, HE Feng
Chin. Phys. Lett. 2004, 21 (2): 233-236 .  
Abstract   PDF(pc) (384KB) ( 392 )
A point collocation method is combined with the Bhatnagar-Gross-Krook (BGK) scheme. The point collocation method is based on reproducing kernel approximations. The BGK scheme developed is evaluated under the finite difference method framework. After the construction of local equilibrium distribution function, the second-order accurate least-square kinetic upwind method is employed to improve the accuracy. Some test cases are explored to validate this meshless method.
An observation of Relationship between the Fine Structure Constant and the Gibbs Phenomenon in Fourier Analysis
ZHOU Zi-Xiang
Chin. Phys. Lett. 2004, 21 (2): 237-238 .  
Abstract   PDF(pc) (258KB) ( 471 )
A value given by a simple mathematical expression is proposed, which is close to the fine structure constant given by 1998 CODATA recommended values of the fundamental physical constants up to relative accuracy 10-7. This expression is related closely with the value of the overshoot of the Gibbs phenomenon in the Fourier analysis.
Evolution and Collision of Bose-Condensed Gases in an Infinitely Deep Square Well
XU Zhi-Jun, LIU Shu-Juan, HUANG Lin, WU Qiang, XIONG Hong-Wei
Chin. Phys. Lett. 2004, 21 (2): 239-242 .  
Abstract   PDF(pc) (343KB) ( 426 )
The evolution and collision of Bose-condensed gases in one-dimensional optical lattices are investigated in the presence of an infinitely deep square well created by two far-off resonant laser beams. The two far-off resonant laser beams are superimposed on the combined potential consisting of a magnetic trap and one-dimensional optical lattices. After the combined potential is switched off, the analytical result of the evolution of the density distribution of the Bose-condensed gas is given by using the propagator method. The collisions between the condensate and the infinitely deep square well are shown in the present work.
Scale-Free Statistics of Bulletin-Board-System Servers Visiting
WANG Wen-Nai, LEE Jaiyong, MI Zheng-Kun
Chin. Phys. Lett. 2004, 21 (2): 243-245 .  
Abstract   PDF(pc) (303KB) ( 1140 )
The scale-free power-law-like signature of statistics of electronic-bulletin-board-system (BBS) servers visiting is reported. The Tsallis entropy approach was employed to fit data sets acquired from servers sited at three Chinese universities. It was found that the exponent of power-law-like probability distribution function, as well as the factor similar to the Langrange multiplier introduced by the maximum entropy principle, probably depends on the number of discussion forums in BBS servers, while the mathematic expectation does not. It was concluded that statistics of BBS visiting is a good realistic candidates for complex networks studies.
Influences of Modulated Noise on Normalized Intensity Fluctuation in a Single-Mode Laser
WANG Jun, CAO Li, , WU Da-Jin,
Chin. Phys. Lett. 2004, 21 (2): 246-249 .  
Abstract   PDF(pc) (349KB) ( 480 )
The influences of the two forms of modulated noises, i.e., the bias signal-modulated noise and the direct signal-modulated noise, on the normalized intensity fluctuation (NIF) are investigated, and the results of the two forms of modulation are compared detailedly. We find that a minimum for the case of the bias signal modulation appears in the curve of the dependence of the NIF upon the quantum and pump noise intensities when the correlation coefficient between the quantum noise and the pump noise is negative. However, the NIF for the case of the direct signal modulation is independent of the correlation coefficient between the two noises. Moreover, at the same parameter region, the NIF for the bias signal modulation is only one-eighth as much as that for the direct signal modulation.
Identification of Chaotic Systems with Application to Chaotic Communication
FENG Jiu-Chao, QIU Yu-Hui
Chin. Phys. Lett. 2004, 21 (2): 250-253 .  
Abstract   PDF(pc) (429KB) ( 448 )
We propose and develop a novel method to identify a chaotic system with time-varying bifurcation parameters via an observation signal which has been contaminated by additive white Gaussian noise. This method is based on an adaptive algorithm, which takes advantage of the good approximation capability of the radial basis function neural network and the ability of the extended Kalman filter for tracking a time-varying dynamical system. It is demonstrated that, provided the bifurcation parameter varies slowly in a time window, a chaotic
dynamical system can be tracked and identified continuously, and the time-varying bifurcation parameter can also be retrieved in a sub-window of time via a simple least-square-fit method.
Phase Synchronization as a Mechanism of Controlling Spatiotemporal Chaos via External Periodic Signal
SANG Hai-Bo, , HE Kai-Fen,
Chin. Phys. Lett. 2004, 21 (2): 254-257 .  
Abstract   PDF(pc) (848KB) ( 431 )
We find that phase synchronization (PS) is a mechanism in which the spatiotemporal chaos (STC) can be suppressed to a spatially regular (SR) state by applying an external periodic signal in a one-dimensional driven drift-wave system. In the driving wave coordinate, the nonlinear system can be transformed to a set of coupled oscillators moving in a periodic potential. In this multi-dimensional system, the internal modes are slaved one by one through PS by the control signal. Two types of responses of the internal modes to the external periodic signal are observed. For some modes, the stabilization is through frequency-locking; while for the other modes, a special kind of PS without frequency-locking, namely multi-looping PS, is developed.

Finite-Temperature Equation of State with Three-Body Force Correlations
LI Zeng-Hua, ZUO Wei, LU Guang-Cheng, YONG Gao-Chan
Chin. Phys. Lett. 2004, 21 (2): 258-261 .  
Abstract   PDF(pc) (512KB) ( 324 )
The equation of state of asymmetric nuclear matter at finite temperature is studied in the framework of the Brueckner-Hartree-Fock approximation which is extended to include three-body force correlations. Due to the additional repulsion produced by three-body force contribution, the proton or neutron potential energy and effective mass are correspondingly enhanced. The symmetry energy gradually becomes more sensitive to the temperature with the increasing density compared with the result that only includes the two hole-line contribution. The asymmetry parameter dependence of symmetry energy is also indicated. It is shown that there is the same linear relation between symmetry energy and β2 as the zero temperature case with β being the asymmetry parameter.
Freestanding a-Si Thin Film Transistor for Room-Temperature Infrared Detection
DONG Liang, YUE Rui-Feng, LIU Li-Tian, ZHANG Wan-Jie
Chin. Phys. Lett. 2004, 21 (2): 262-265 .  
Abstract   PDF(pc) (460KB) ( 406 )
We present the fabrication and characterization of a novel uncooled infrared sensor for room-temperature infrared imaging. The sensitive element of the sensor is a freestanding amorphous silicon thin film transistor (a-Si TFT) with the temperature coefficient of the drain current (TCC) of 0.015-0.08/K. The TCC value is sensitive to the ambient temperature and can be controlled by the gate voltage of the a-Si TFT. The complete procedures based on the porous silicon micromachining technique for fabricating thermally isolated air bridges are described. The isolation structures have a thermal conductance of 5 x 10-6W/K and a thermal capacitance of 4.9 x 10-8J/K. The effects of the gate voltage on the performance figures such as responsivity, noise voltage and detectivity are described and analysed in details. The maximum detectivity reaches 4.33 x 10-8cmHz1/2W-1 at a chopping frequency of 27 Hz and a gate voltage of -15 V.
Ellipsometric Spectra and Optical Properties of Anisotropic SrBi2Ta2O9 Films
MO Dang, LIU Yi, G. D. Hu, J. B. Xu
Chin. Phys. Lett. 2004, 21 (2): 266-268 .  
Abstract   PDF(pc) (341KB) ( 435 )
Ellipsometric spectra of the SrBi2Ta2O9 (SBT) films of (200) and (0010) predominant orientation are measured and analysed in the range of photon energy from 2 to 5 eV. The results show that the oriented SBT films appear to be strongly anisotropic. The ellipsometric spectra of the (200)-predominant SBT films are different from those of the (0010)-predominant films. We suggest an analysis model for these oriented films and perform the fitting of the anisotropic ellipsometric spectra. The refractive index and the extinction coefficient of the ordinary ray and the extraordinary ray for these oriented SBT films are obtained. The ordinary refractive index is larger than the extraordinary one.
Calculation of Energy Levels of Nucleus 127I in the Particle-Triaxial-Rotor Model
SONG Hui-Chao, LIU Yu-Xin, , ZHANG Yu-Hu
Chin. Phys. Lett. 2004, 21 (2): 269-272 .  
Abstract   PDF(pc) (368KB) ( 353 )
Theoretical calculations have been performed for nucleus 127I in the framework of the particle-triaxial-rotor model. The calculated results indicate that both the 5/2+ and 7/2+ bands are oblate deformed bands. Their configurations are associated with the πd5/2[4 0 2]5/2 and πg7/2[4 0 4]7/2 orbitals and the strong mixing between them. Meanwhile a possible explanation of the strong mixing is given.

Direct Radiative Capture of Neutron in Drip-Line Nuclei
LIU Zu-Hua, ZHANG Xi-Zhen, ZHANG Huan-Qiao
Chin. Phys. Lett. 2004, 21 (2): 273-275 .  
Abstract   PDF(pc) (316KB) ( 434 )
The analytic expressions of radial matrix elements < lc = 0|r|lh = 1>, < lc = 1|r|lh = 0> and < lc = 1|r|lh = 2> in a finite square-well potential are derived.Based on these analytic expressions of radial matrix elements the neutron direct radiative capture (DRC) processes leading to bound p-orbit from incident s-wave, and leading to s- and d-orbits from incident p-wave are discussed. For the DRC processes leading to loosely bound orbits, the dominant contributions to the radial matrix elements come from the outer region of nuclear potential radius R.

Isotope Effects of Solid Hydrogenic Pellet Ablation
DENG Bai-Quan, PENG Li-Lin, YAN Jian-Cheng, WANG Xiao-Yu
Chin. Phys. Lett. 2004, 21 (2): 276-278 .  
Abstract   PDF(pc) (323KB) ( 668 )
The isotope effects of ablation processes in fusion plasma for five combinations of solid isotopic hydrogenic pellets H2, HD, D2, DT, and T2 have been studied for the first time to our knowledge. The results show that the modifications caused by isotope effects for pellet erosion speeds range from 1 for hydrogen pellet down to 0.487 for tritium pellet and are not negligible in ablation rate calculations. These effects can lead to deeper mass deposition and improved core fueling efficiency.

Momentum Transfer Dependence of Two Types of the Broad Enhancement Phenomena: CO Spectra in the Valence Energy Region
ZHONG Zhi-Ping, HAN Xiao-Ying, ZHANG Wei-Hua, LI Jia-Ming,
Chin. Phys. Lett. 2004, 21 (2): 279-282 .  
Abstract   PDF(pc) (481KB) ( 571 )
Partial generalized oscillator strength densities of CO molecules related to the excitation of a 5σ or 1π electron are calculated by using multi-scattering self-consistent-field methods. Momentum transfer dependence of two types of the broad enhancement phenomena above the threshold with one-electron character, i.e. shape resonance and non-resonance enhancement, is studied. Our calculations show that the energy position of a non-resonance enhancement is related to the momentum transfer K. Therefore, electron impact based experiments can be used to identify the two types of the broad enhancement phenomena.

Application of Time-Dependent Density-Functional Theory to C6
ZHOU Xiao-Lin, BAI Yu-Lin, CHEN Xiang-Rong, YANG Xiang-Dong,
Chin. Phys. Lett. 2004, 21 (2): 283-286 .  
Abstract   PDF(pc) (326KB) ( 586 )
We employ a real-space pseudopotential method to determine the ground state structure of the carbon cluster C6 via simulated annealing and the corresponding optical absorption spectra from the adiabatic time-dependent density-functional theory (TDDFT) and the local density approximation (TDLDA). It is found that the ground state structure of the carbon cluster C6 belongs to a monocyclic D3h structure and the calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations.

Spectra of Highly Ionized Sulfur below 200Å
YANG Zhi-Hu, WANG You-De, MA Xin-Wen, LIU Hui-Ping, SU Hong, ZHANG Yan-Ping, XIAO Guo-Qing
Chin. Phys. Lett. 2004, 21 (2): 287-290 .  
Abstract   PDF(pc) (305KB) ( 503 )
Spectra of carbon-, boron-, beryllium-, lithium-, helium-, and hydrogen-like sulfur ions were obtained and studied for the wavelengths below 200Å and the energy of 80 MeV by using beam-foil method. Thirty-five lines have been identified, in which fifteen lines are newly accurately measured. The spectra were analysed based on the theoretical results and other experimental data.
Optical Transition Probability of Sm3+ Ions in a Polymer Optical Fiber
ZHENG Zhi-Qiang, LIANG Hao, MING Hai, ZHANG Qi-Jin, HAN Xin-Hai, WANG Guan-Zhong, XIE Jian-Ping
Chin. Phys. Lett. 2004, 21 (2): 291-294 .  
Abstract   PDF(pc) (315KB) ( 601 )
We investigate optical absorption and emission spectra of Sm3+ ions in Sm(DBM)3Phen-doped polymethyl methacrylate (PMMA). Based on the Judd-Ofelt theory, the optical intensity parameters are calculated to be Ω2 = 13.76 x 10-20cm2, Ω4 = 3.41 x 10-20cm2, Ω6 = 4.01 x 10-20cm23 Phen-doped polymethyl methacrylate. The optical intensity parameters have been used to calculate the total radiative transition rate (676.57 s-1) and radiative lifetime (147 μs) of the 4G5/2 exciting state. The stimulated emission cross-sections σij and the fluorescence branch ratios for the 4G5/26FJ' and 4G5/26FJ' transitions are also evaluated. The analysis reveals that Sm(DBM)3Phen-doped PMMA is promising for applications in rare-earth-doped polymer devices.

Degenerate Four-Wave Mixing in SO2 in Free Jets
CHEN De-Ying, FAN Rong-Wei, YANG Xin-Ju, ZHENG Qi-Ke, QIN Qi-Zong
Chin. Phys. Lett. 2004, 21 (2): 295-297 .  
Abstract   PDF(pc) (416KB) ( 449 )
A rotational excitation spectrum of SO2 [ A 1A2 (511) ← X1A1 (000)] at about 33331 cm-1 in free jets was observed by using the forward degenerate four wave mixing (DFWM). Twelve lines of the G band and eleven ones of the E band were marked based on the rotational constants according to Hamada's result [Can. J. Phys. 53 (1975) 2555]. The relation between the DFWM signal intensity and the pressure of the buffer gas in free-jets was experimentally investigated.

Generation of a Dark Hollow Beam inside a Cavity
ZHANG Lei, LU Xuan-Hui, CHEN Xu-Min, HE Sai-Ling
Chin. Phys. Lett. 2004, 21 (2): 298-301 .  
Abstract   PDF(pc) (452KB) ( 385 )
A new method is introduced to generate a hollow beam inside a cavity. Using a matrix eigenvalue method, the laser resonator with optical diffraction elements is theoretically analysed and simulated. The hollow beam can be obtained theoretically by controlling the parameters of the diffraction functions. After designed the diffraction components in the cavity, a hollow beam of good quality is realized experimentally using a YAG solid state laser.
Coalescence and Anti-Coalescence Interference of Two-Photon Wavepacket in a Beam Splitter
WANG Kai-Ge, YANG Guo-Jian
Chin. Phys. Lett. 2004, 21 (2): 302-305 .  
Abstract   PDF(pc) (386KB) ( 383 )
We study theoretically the interference of a two-photon wavepacket in a beam splitter. We find that the spectrum symmetry for the two-photon wavepacket dominates the perfect coalescence and anti-coalescence interference. The coalescence interference is unrelated to photon entanglement. Only the anti-coalescence interference has evidence of photon entanglement. We prove that the two-photon wavepacket with an anti-symmetric spectrum is transparent to pass the 50/50 beam splitter, showing perfect anti-coalescence interference.

Suppression and Enhancement in Parametric Two-Photon Resonant Nondegenerate Four-Wave Mixing via Quantum Interference
SUN Jiang, MI Xin, YU Zu-He, JIANG Qian, ZUO Zhan-Chun, WANG Yan-Bang, WU Ling-An, FU Pan-Ming
Chin. Phys. Lett. 2004, 21 (2): 306-309 .  
Abstract   PDF(pc) (392KB) ( 413 )
Quantum interference may lead to suppression and enhancement of
the two-photon resonant nondegenerate four-wave mixing signal in a cascade four-level system. Such phenomena are emonstrated in Ba through inducing atomic coherence between the ground state 6s2 and the doubly excited autoionizing Rydberg state 6pnd. This method can be used as a new spectroscopic tool for measuring the transition dipole moment between two highly excited atomic states.

Wide-Band Polarisation-Insensitive High-Output-Power Semiconductor Optical Amplifier Based on Thin Tensile-Strained Bulk InGaAs
WANG Shu-Rong, LIU Zhi-Hong, WANG Wei, ZHU Hong-Liang, ZHANG Rui-Ying, ZHOU Fan, WANG Lu-Feng, DING Ying
Chin. Phys. Lett. 2004, 21 (2): 310-312 .  
Abstract   PDF(pc) (329KB) ( 644 )
A polarization-insensitive semiconductor optical amplifier (SOA) with a very thin active tensile-strained InGaAs bulk has been fabricated. The polarization sensitivity of the amplifier gain is less than 1 dB over both the entire range of driving current and the 3 dB optical bandwidth of more than 80 nm. For optical signals of 1550 nm wavelength, the SOA exhibits a high saturation output power +7.6 dBm together with a low noise figure of 7.5 dB, fibre-to-fibre gain of 11.5 dB, and low polarization sensitivity of 0.5 dB. Additionally, at the gain peak 1520 nm, the fibre-to-fibre gain is measured to be 14.1 dB.

Diode-Pumped Self Q-Switched and Mode-Locking Nd3+, Cr4+:YAG Laser
LI Chun-Yong, LI Ping-Xue, LI De-Hua, FENG Bao-Hua, FU Pan-Ming, ZHANG Zhi-Guo, ZHANG Shi-Wen
Chin. Phys. Lett. 2004, 21 (2): 313-315 .  
Abstract   PDF(pc) (508KB) ( 533 )
Using Nd3+, Cr4+:YAG as a laser crystal and saturable absorber simultaneously, we obtain a self-Q-switched and mode-locking laser at 1.06 μm with straight cavity structure. Self mode-locking phenomenon was observed at an intracavity intensity of only about 2000 W/cm1. More than 90% modulation depth is achieved at an intracavity intensity of less than 3.0 x 104 W/cm2 for the first time. The Q-switched pulse width and repetition rate are found to be connected with the cavity length and the output power.
Design of Synthesized DBRs for Long-Wavelength InP-Based Vertical-Cavity Surface-Emitting Lasers
HUANG Zhan-Chao, WU Hui-Zhen
Chin. Phys. Lett. 2004, 21 (2): 316-319 .  
Abstract   PDF(pc) (393KB) ( 1125 )
We report applications of a metallic film and a phase matching layer (PML) to increase the reflectivity of the cavity mirror in a long-wavelength InP-based vertical-cavity surface-emitting laser (VCSEL). The synthesis of the InGaAsP/InP distributed-Bragg reflector (DBR) with an Au film and the InP PML leads to the decrease of periods of the DBR multilayer stacks from 33 to 20 while keeping the reflectivity of the structure over 99%. The reflectivity over the whole forbidden band is significantly increased and become flatter compared to the bare DBR. The use of smaller DBR periods in a long wavelength VCSEL makes the epitaxial growth well controllable, decrease of the heat resistance, and decrease of the in-series electrical resistance of the devices. This can improve the reliability of the VCSEL growth and possibly cut down the cost of VCSEL devices.

Short-Wavelength Recording Properties of TeOx Thin Films
LI Qing-Hui, GU Dong-Hong, GAN Fu-Xi
Chin. Phys. Lett. 2004, 21 (2): 320-323 .  
Abstract   PDF(pc) (368KB) ( 757 )
We prepare TeOx thin films by vacuum evaporation of TeO2 powder. It is found that the as-deposited TeOx films can represent a two-component system comprising crystalline tellurium particles dispersed in an amorphous TeO2 matrix. Results of the static recording test show that the TeOx films have good writing sensitivity for short-wavelength laser beam (514.5 nm). Primary results of the dynamic recording test at 514.5 nm are also reported. The carrier-to-noise ratio of 30 dB is obtained for the disk using a TeOx film as the recording medium. Atomic force microscopy is used to study the microstructure of recorded marks. Micro-area morphology images show that the marks are mechanically deformed, and depressions and bulges have been imaged in the recorded marks, resulting in the scattering of the reading laser beam. The analytical results of transmission electron microscopy show that there is not obvious difference between the phase states of the tellurium particles before and after laser irradiation. Recording mechanism of the TeOx thin films are discussed based on the experimental results.
Band Gaps of an Amorphous Photonic Materials
WANG Yi-Quan, FENG Zhi-Fang, HU Xiao-Yong, CHENG Bing-Ying, ZHANG Dao-Zhong
Chin. Phys. Lett. 2004, 21 (2): 324-325 .  
Abstract   PDF(pc) (337KB) ( 633 )
A new kind of amorphous photonic materials is presented. Both the simulated and experimental results show that although the disorder of the whole dielectric structure is strong, the amorphous photonic materials have two photonic gaps. This confirms that the short-range order is an essential factor for the formation of the photonic gaps.

Compact First-Order Polarization Mode Dispersion Compensator Based on Birefringent Crystals
YANG Chang-Xi, LI Shi-Guang, MIAO Hou-Xun, TIAN Yu, ZHANG En-Yao, JIN Guo-Fan
Chin. Phys. Lett. 2004, 21 (2): 326-328 .  
Abstract   PDF(pc) (441KB) ( 612 )
We report a new first-order polarization-mode-dispersion (PMD) compensator based on birefringent crystals and magneto-optic polarization controllers. The compensator shows the response time of 150μs, insertion loss smaller than 3 dB, and maximum differential group delay of 44.6 ps. Compared to the first-order PMD compensators reported so far, our PMD compensator exhibits fast response time, low insertion loss, compact size, broad bandwidth, and immunity to environmental vibrations.
Characterization of Amplified Spontaneous Emission from Er3+-Doped Tellurite Fiber
DAI Shi-Xun, ZHANG Jun-Jie, LI Shun-Guang, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2004, 21 (2): 329-331 .  
Abstract   PDF(pc) (352KB) ( 416 )
We present the characterization of amplified spontaneous emission (ASE) from newly fabricated Er3+-doped tellurite fibers. When pumped at 980 nm, a very broad erbium ASE in the range 1450-1650 nm is observed. The changes of ASE with regard to fiber lengths and pumping power were measured. The output of 2 mW from an Er3+-doped tellurite fiber ASE source is obtained with the pump power of 540 mW.

A New Method for Filter Design Based on Long-Period Fiber Grating
CHEN Kai, SHENG Qiu-Qin, DONG Xiao-Yi
Chin. Phys. Lett. 2004, 21 (2): 332-334 .  
Abstract   PDF(pc) (392KB) ( 475 )
We present a simple method to induce mechanically a long-period fiber grating in a general sing mode fiber. The transmission spectrum of the new type of grating can be tailored by changing the external applied pressure or by introducing a phase-shift in the grating. The tunability this kind of gratings exhibit will be particularly useful for the filter design.

Measurement of Root-Mean-Square Phase Errors in Arrayed Waveguide Gratings
ZHENG Xiao-Ping, CHU Yuan-Liang, ZHAO Wei, ZHANG Han-Yi, GUO Yi-Li
Chin. Phys. Lett. 2004, 21 (2): 335-336 .  
Abstract   PDF(pc) (320KB) ( 454 )
The interference-based method to measure the root-mean-square phase errors in SiO2-based arrayed waveguide gratings (AWGs) is presented. The experimental results show that the rms phase error of the tested AWG is 0.72 rad.

Time Reversal Self-Focusing in a Solid-Plate Waveguide
ZHANG Bi-Xing, WU Hao, WANG Cheng-Hao
Chin. Phys. Lett. 2004, 21 (2): 337-340 .  
Abstract   PDF(pc) (512KB) ( 422 )
Acoustical self-adaptive focusing in a solid-plate waveguide is theoretically and experimentally studied. The multi-path effect exists in the solid plate. A pulse will be widened into a pulsed train and the waveform is distorted. The time-reversal mirrors are applied to study the self-adaptive focusing. The time-reversal effect can be characterized by the focusing gain and the ratio of the principal to the second lobe. It is found theoretically and experimentally that the time reversal mirrors can compensate automatically for the waveform distortion caused by the multi-path effect.

Visual-Width of an Ultrasonic Gaussian Beam on the Schlieren Photograph and Explanation to the Nonspecularly Reflected Sound Field
ZHU Guo-Zhen, SUN Yao, FU De-Yong
Chin. Phys. Lett. 2004, 21 (2): 341-344 .  
Abstract   PDF(pc) (300KB) ( 524 )
On the schlieren photograph, a continuous ultrasonic Gaussian beam and its nonspecularly reflected beams [Chin. Phys. Lett. 16 (1999) 819] always have limited visual-width, although the theoretical spatial distribution of the sound field is a continuous function. To study this problem, the first step is to investigate the visual-width of the beam on the photograph related to the sound pressure at the centre of the beam by the threshold of the optical system caused by the refraction of light; the second step is to explain the visual-width of nonspecularly reflected field. By applying a relevant threshold, checked by the visual width of the incident beam, to cut the theoretical curves of the reflected sound field, one can find the visual-width of the two reflected beams and the gap between them are correspondent to that on the schlieren photograph.

Freezing-Thawing Characteristics of Botanical Tissues and Influence of Water Morphology
WU Hai-Ling, MA Yuan, PENG Xiao-Feng
Chin. Phys. Lett. 2004, 21 (2): 345-347 .  
Abstract   PDF(pc) (325KB) ( 383 )
A series of visualization experiments were conducted to investigate the transport phenomena and interface behaviour during the freezing-thawing process of typical botanical tissues. Attentions were paid to the growth of ice crystals and the advancing of the phase-change interface. The comparison was made to identify the freezing/thawing behaviour for different tissues under various freezing conditions. Based on the experimental observation, analyses were conducted to explore the influence of water morphology on the freezing/thawing characteristics.
Inner Structure of Boiling Nucleus and Interfacial Energy Between Nucleus and Bulk Liquid
WANG Xiao-Dong, TIAN Yong, PENG Xiao-Feng, WANG Bu-Xuan
Chin. Phys. Lett. 2004, 21 (2): 348-351 .  
Abstract   PDF(pc) (267KB) ( 437 )
A model of two-region structure of a nucleus is proposed to describe nucleus evolution. The interfacial tension between bulk liquid phase and nucleus is dependent on the density gradient in the transition region and varies with the structure change of the transition region. With the interfacial tension calculated using this model, the predicted nucleation rate is very close to the experimental measurement. Furthermore, this model and associated analysis provide the solid theoretical evidences to clarify the definition of nucleation rate and understand nucleation phenomenon with the insight into the physical nature.

A Stationary Vortex Phenomenon above a Low-Aspect-Ratio Wing
TANG Jian, ZHU Ke-Qin, TAN Guang-Kun
Chin. Phys. Lett. 2004, 21 (2): 352-355 .  
Abstract   PDF(pc) (955KB) ( 496 )
A stationary vortex phenomenon above a nondelta low-aspect-ratio wing was obtained in three-dimensional unsteady numerical simulation. Flow visualization is conducted in water-channel using hydrogen bubbles. The results verify that there is a vortex trapped above the low-aspect-ratio wing and the stationary vortex is consisted of two semi-balls and anti-rotation vortices which are different from the leading edge vortices on the delta wing.
Effects of Liquid Second Viscosity in High-Amplitude Sonoluminescence
Ahmad Moshaii, Rasool Sadighi-Bonabi, Mohammad Taeibi-Rahni, Mehdi Daemi
Chin. Phys. Lett. 2004, 21 (2): 356-359 .  
Abstract   PDF(pc) (508KB) ( 457 )
The well-known Rayleigh-Plesset (RP) equation is the base of nearly all hydrodynamical descriptions of sonoluminescence (SL) phenomenon. A major deficiency of this equation is that it accounts for viscosity of an incompressible liquid and compressibility, separately. By removing this approximation, we have modified the RP equation considering effects of liquid second viscosity. This modification exhibits its importance at the end of an intense collapse, so that the new model predicts appearance of a new picosecond bouncing during high amplitude sonoluminescence radiation. This new bouncing produces very sharp (sub-picosecond) peaks on the top of sonoluminescence pulse. These new behaviors are more remarkable for higher driving pressures and lower ambient temperatures.
Sawtooth-Stabilization and Snake-Excitation during LHCD on the HL-1M
LIU Yi, QIU Xiao-Ming, DONG Yun-Bo, GUO Gan-Cheng, ZHONG Yun-Ze, FU Bing-Zhong, LIU Yong
Chin. Phys. Lett. 2004, 21 (2): 360-363 .  
Abstract   PDF(pc) (650KB) ( 871 )
Lower-hybrid current drive (LHCD) experiments were carried out in the HL-1M hydrogen plasmas. The suppression of sawtooth instabilities by LHCD has been observed in the sawtoothing discharges, an improvement in the global energy confinement time of up to 20% is observed. There is an optimal rf-power range for the complete suppression of the central MHD instabilities. Possible mechanisms for the stabilization of the sawtooth instability are discussed from the measurement of internal inductance and current profile reconstruction using an equilibrium code. A large long-lived snake-like oscillation is newly observed at the end of sawtooth-stabilization phase of the LHCD operation in the HL-1M tokamak. It is evident that such perturbation is due to a temperature depression caused by impurity accumulation during LHCD.

Secondary-Electron Emission Effects in Plasma Immersion Ion Implantation with Dielectric Substrates
LI Xue-Chun, WANG You-Nian
Chin. Phys. Lett. 2004, 21 (2): 364-366 .  
Abstract   PDF(pc) (325KB) ( 478 )
Using a dynamic sheath model, we have studied the secondary-electron emission effects at one-dimensional planar dielectric surface in plasma immersion ion implantation. The temporal evolution of the sheath thickness, the surface potential of dielectric, and the ions dose accumulated on the dielectric surface are obtained. The numerical results demonstrate that the charging effects is greatly enhanced by the secondary electron emission effects, so the sheath thickness becomes thinner, the surface potential of dielectric decreases fast and the ions dose accumulated on the dielectric surface significantly increases.
CdZnTe Energy Levels Induced by Doping of Indium
LI Guo-Qiang, JIE Wan-Qi, GU Zhi, YANG Ge, WANG Tao
Chin. Phys. Lett. 2004, 21 (2): 367-369 .  
Abstract   PDF(pc) (260KB) ( 408 )
Photoluminescence (PL) and infrared transmission spectra are used to characterize the In-doped Cd0.9Zn0.1Te (CdZnTe:In). The PL spectrum reveals that there are two other strong emissions situated at 1.54 eV and 1.62 eV except the near band edge emission. This indicates that the doped In can lead to two donor levels of 0.12 eV and 0.04 eV in the CdZnTe band construction, respectively. The IR transmission spectra show that when the wavenumber is larger than 1000cm-1, the CdZnTe:In was almost opaque to the IR emission. Then its IR transmission rapidly increases to 52% when the wavenumber is decreased to 350cm-1 and then keeps to be constant. This confirms the existence of the donor level of 0.12 eV.

Dynamic Localization Condition of Two Electrons in a Strong dc-ac Biased Quantum Dot Molecule
WANG Li-Min, DUAN Su-Qing, ZHAO Xian-Geng, LIU Cheng-Shi
Chin. Phys. Lett. 2004, 21 (2): 370-373 .  
Abstract   PDF(pc) (277KB) ( 350 )
We present a perturbation investigation of dynamic localization condition of two electrons in a strong dc-ac biased quantum dot molecule. By reducing the system to an Hubbard-type effective two-site model and by applying Floquet theory, we find that the dynamical localization phenomenon occurs under certain values of the large strength of the dc and ac field. This demonstrates the possibility of using appropriate dc-as fields to manipulate dynamical localized states in mesoscopic devices, which is an essential component of practical schemes for quantum information processing. Our conclusion is instructive to the field of quantum function devices.

Low Temperature Specific Heat of the Underdoped La2-xSrxCuO4 Single Crystals
LIU Zhi-Yong, YANG Hai-Peng, LU Xi-Feng, ZHOU Fang, WEN Hai-Hu
Chin. Phys. Lett. 2004, 21 (2): 374-377 .  
Abstract   PDF(pc) (696KB) ( 606 )
We report the low-temperature specific heat of La2-xSrxCuO4 (x = 0.063) single crystals before and after annealing in the temperature region of 2-10 K and magnetic fields up to 12 T. The data confirm the √H dependence of the linear term coefficient γ predicted for d-wave paring in the Volovik theory at T = 0 K. However, the data do not satisfy the proposed Simon-Lee scaling law at finite temperatures, i.e., CDOS/(T2) = f(T/√H), where f is an unknown scaling function and CDOS is the extra specific heat contributed by the nodal quasiparticles due to the Doppler effect. Possible reasons for this failure are presented.

Phase Diagrams and Tricritical Behaviour of the Spin-2 Ising Model in a Longitudinal Random Field
Chin. Phys. Lett. 2004, 21 (2): 378-381 .  
Abstract   PDF(pc) (380KB) ( 707 )
Within the framework of the effective-field theory with correlations, we study the ferromagnetic spin-2 random-field Ising model (RFIM) in the presence of a crystal field on honeycomb (z = 3), square (z = 4) and simple cubic (z = 6) lattices. The effects of the crystal field and the longitudinal random field on the phase diagrams are investigated. Some characteristic features of the phase diagrams, such as the tricritical phenomena, reentrant phenomena and existence of two tricritical points, are found.

Effects of Ag Doping on Magnetoresistance of La0.833K0.167MnO3 Polycrystalline Perovskite Manganites
WU Jian, ZHANG Shi-Yuan
Chin. Phys. Lett. 2004, 21 (2): 382-385 .  
Abstract   PDF(pc) (644KB) ( 521 )
The microstructure, magnetic and transport properties of the heterogeneous system with a nominal composition (1/m)Ag2O-La0.833K0.167MnO3 (1/m is molar ratio with m = 32, 16, 8, 4, and 2) have been studied. The x-ray diffraction patterns show that all the samples are the two-phase composite and consist of a magnetic La0.833K0.167MnO3 (LKMO) perovskite phase and a nonmagnetic metal Ag phase. The room-temperature magnetoresistance (MR) effect is enhanced significantly due to the addition of Ag. For the m = 4 sample, we obtain the MR values up to 32% under a lower field of 0.5 T and 67% under a higher field of 5.5 T at the temperature of 300 K, which are much larger than the corresponding MR values (10% and 35%) of the LKMO sample without Ag. In the low temperature range from 4.2 K to 250 K, the MR values of the Ag-added samples however decrease with the increasing Ag content in the samples. The effect is discussed qualitatively by using the relative contribution from the intrinsic MR effect and the extrinsic MR effect including the spin-polarized-tunneling and spin-dependent scattering effects in different temperature regions.
Synthesis and Magnetic Properties of the Intercalation Compound FePS3(CoCp2)0.40
LIN Jun, DAI Yao-Dong, HE Yun, HUANG Hong-Bo, XIAO Fan, XIA Yuan-Fu
Chin. Phys. Lett. 2004, 21 (2): 386-388 .  
Abstract   PDF(pc) (335KB) ( 402 )
Intercalation compound FePS3(CoCp2)0.40 (CoCp2 = cobaltocene) was synthesized, and the crystal structure and magnetic properties were studied by x-ray diffraction, magnetic susceptibility measurement, and Mössbauer spectroscopy. The crystal structure was indexed to monoclinic unit cell with a = 5.996Å, b = 10.106Å c = 12.511Å, β = 105.916°, and about 5.6Å expansion at the c direction compared to pure FePS3. The Mössbauer spectra indicate that there are three kinds of divalent irons with high spin state in the intercalation compound, which implies that charge transfer from guest to the Fe-S e*g anti-bonding orbits of host lattice. No cationic vacancies are formed in the intercalation compound. The ferromagnetism at low temperature originates from the spin canting of divalent irons.
Numerical Calculation of Kerr Spectra for Magnetic Granular Films
LIN Ying-Bin, HUANG Zhi-Gao, DU You-Wei
Chin. Phys. Lett. 2004, 21 (2): 389-392 .  
Abstract   PDF(pc) (728KB) ( 453 )
Based on the 4 x 4 matrix method, we present theoretical calculations of the magneto-optic polar Kerr effect with the incident energy in granular films. It is found that the simulated results are in good agreement with experimental ones. In addition, Kerr rotation and ellipticity as functions of incident angle and magnetic film thickness have been computed. The calculated results indicate that the Kerr spectra as a function of the incident angle reveal maximum at certain incident angles and the Kerr spectra appear a periodical and damped oscillation with the magnetic thickness, which is important for design of the materials in the future.

Cathodoluminescence and Magnetic Properties of Mn+ Implanted AlN
LI Ming-Kai, LI Cheng-Bin, LIU Chuan-Sheng, FAN Xiang-Jun, FU De-Jun, SHON Yun, KANG Tae-Won
Chin. Phys. Lett. 2004, 21 (2): 393-395 .  
Abstract   PDF(pc) (384KB) ( 429 )
The III-V wide band gap semiconductors show the potential in applications for dilute magnetic semiconductors. AlN films are implanted with 20-keV Mn+ ions with a dose of 5 x 1016cm-2. The cross section of as-implanted AlN are investigated by field-emission scanning electron microscopy and the energy dispersive spectra. The result confirms that the implantation depth is about 100 nm. Cathodoluminescence measurements show that the main peak at 2.6 eV attributed to a donor-to-Mn2+ transition. It is argued that the Mn element in AlN can act as a p-type dopant peak at 2.07 eV. The magnetic measurement shows a transition temperature of 100 K in the implanted AlN annealed at 500°C for 30 min. Clear ferromagnetic hysteresis was observed at 77 K, with a coercive field of 212.7 Oe.
Structure, Electrical, and Optical Properties of Nb-doped BaTiO3 Thin Films Grown by Laser Molecular Beam Epitaxy
GUO Hai-Zhong, LIU Li-Feng, LU Hui-Bin, FEI Yi-Yan, XIANG Wen-Feng, ZHOU Yue-Liang, CHEN Zheng-Hao
Chin. Phys. Lett. 2004, 21 (2): 396-399 .  
Abstract   PDF(pc) (449KB) ( 653 )
Structure, electrical, and optical properties of Nb-doped BaTiO3 (Nb:BTO) thin films on MgO substrates grown by laser molecular beam epitaxy with the increasing Nb content were investigated. The Nb:BTO thin films with high crystallinity are epitaxially grown on MgO substrates. With more Nb-doped content, the impurity phases are found in Nb:BTO thin films. Hall measurement at room temperature confirms that the charge carriers of the Nb:BTO thin films are n-type. When the Nb-doped content increases, the carrier concentration and carrier mobility increase. Meanwhile the optical transmittance decreases with the increase of the Nb-doping, and the width of the forbidden band in each group is not affected by the presence of Nb in the samples. Raman spectra show that the structural phase transition may occur with the increase of the Nb-doping content, in the meantime more defects and impurities exist in the Nb:BTO thin films.
Structural and Electrical Properties of Amorphous Hydrogen Carbon-Nitrogen Films
SUO Da-Cheng, LIU Yi-Chun, LIU Yan, QI Xiu-Ying, ZHONG Dian-Qiang
Chin. Phys. Lett. 2004, 21 (2): 400-402 .  
Abstract   PDF(pc) (319KB) ( 446 )
Amorphous hydrogenated carbon-nitrogen (a-C:H:(N)) films with different nitrogen contents have been deposited by using rf-sputtering of a high purity graphite target in an Ar-H2-N2 atmosphere. Transmittance and reflectance spectra are used to characterize the Tauc gap and absorption coefficients in the wavelength range 0.185-3.2μm. The temperature dependence of conductivity demonstrates a hopping mechanism of the Fermi level in the temperature range of 77-300 K. The density of state at the Fermi level is derived from the direct current conductivity. The photoluminescence properties of a-C:H:N films were investigated. The photoluminescence peak has a blue shift with increasing excitation energy. These results are discussed on the basis of a model in which the different sp2 clusters dispersed in sp3 matrices.

An Experimental Analysis of Residual Stress Measurements in Porous Silicon Using Micro-Raman Spectroscopy
LEI Zhen-Kun, KANG Yi-Lan, HU Ming, QIU Yu, XU Han, NIU Hong-Pan
Chin. Phys. Lett. 2004, 21 (2): 403-405 .  
Abstract   PDF(pc) (314KB) ( 1146 )
Micro-Raman spectroscopy of porous silicon films of micrometers and on silicon bulk substrates is carried out. The practical information is given for applications of stress measurements in the films which were obtained with electrochemical etching technique. Higher residual stress (reached GPa) in the etched area falls continuously through the transitional area to the un-etched area of the sample. However, the stress gradient is smaller in the etched or un-etched area and increases in the transitional area between the two areas. Using atomic force microscopy to investigate surface appearance of porous silicon films, micro-cavity structure is expected to relate to the distribution of residual stress.

Induced Nucleation of Diamond Films on ZnS Substrates Precoated with Ceramic Interlayer
GAO Xu-Hui, LU Fan-Xiu, TONG Yu-Mei, GUO Hui-Bin, TANG Wei-Zhong, LI Cheng-Ming, CHEN Guang-Chao, YU Huai-Zhi, CHENG Hong-Fan, YANG Hai
Chin. Phys. Lett. 2004, 21 (2): 406-409 .  
Abstract   PDF(pc) (432KB) ( 492 )
We attempt to coat a multi-spectrum chemical-vapor-deposition ZnS substrate with smooth crystalline diamond films on the top of properly designed ceramic interlayer, which provides protection for ZnS against corrosion by the H2-CH4 microwave plasma and mitigates the thermal expansion coefficient mismatching between diamond and ZnS. However, difficulties in the homogenous diamond nucleation on a ceramic interlayer were encountered. It was found that high rate nucleation of diamond could be induced by a metal or semiconductor mask placed on the top of ZnS.
Two-Step Growth of MgO Films on Sapphire (0001) Substrates by Radio Frequency Plasma-Assisted Molecular Beam Epitaxy
MEI Zeng-Xia, DU Xiao-Long, ZENG Zhao-Quan, GUO Yang, WANG Jian, JIA Jin-Feng, XUE Qi-Kun
Chin. Phys. Lett. 2004, 21 (2): 410-413 .  
Abstract   PDF(pc) (368KB) ( 894 )
We report on the growth of rock salt MgO films on sapphire (0001) substrates by rf plasma-assisted molecular beam epitaxy. A two-step method, i.e., high temperature epilayer growth after low-temperature buffer layer growth, was adopted to obtain the single crystal MgO film. The epitaxial orientationship between the MgO epilayer and the sapphire (0001) substrate was studied by using in-situ reflection high energy electron diffraction and ex-situ x-ray diffraction, and it is found that the MgO film grows with [111] orientation. The role of the low temperature buffer layer in the improvement of crystal quality of the MgO epilayer is discussed based on the cross-sectional scanning electron microscopy.
Analysis and Optimal Design of a Novel SiGe/Si Power Diode for Fast and Soft Recovery
GAO Yong, MA Li
Chin. Phys. Lett. 2004, 21 (2): 414-417 .  
Abstract   PDF(pc) (453KB) ( 729 )
We propose a novel p+ (Si1-xGex-n--n+ hetero-junction power diode with three-step gradual changing doping concentration in the base region, and the structure mechanism is analysed. The fast and soft reverse recovery characteristics have been obtained and the optimal design of the changing doping concentration gradient and the percentage of Ge is carried out. Compared to the conventional structure of p+ (Si1-xGex-n--n+ with a constant doping concentration, the softness factor S increases nearly two times, the reverse recovery time and the peak reverse current are reduced over 15% for the device with the optimized concentration gradient, while the forward drop is almost unchanged. Taking into account of the improvement of the whole characteristics of the novel device, we obtain the optimal percentage of Ge to be 20%.
Orbital Phase Dependence of Globular Cluster’s Tidal Radii
WU Zhen-Yu, ZHOU Xu, MA Jun
Chin. Phys. Lett. 2004, 21 (2): 418-420 .  
Abstract   PDF(pc) (285KB) ( 340 )
The orbits for a sample of 45 galactic globular clusters are calculated using positions and spatial velocities based on recent compilations as well as new measurements of their absolute proper motions. The perigalactic positions of each cluster are used to determine their theoretical tidal radii in the given galactic model. The orbital phase dependence between the theoretical and observed tidal radii is evidenced.

57 articles