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Vol. 57, No. 5 (2008)

2008-03-05
GENERAL
Microwave processes in a RF photoinjector
Yang Zhen-Ping, Li Zheng-Hong
2008, 57 (5): 2627-2632. doi: 10.7498/aps.57.2627
Abstract +
The equivalent-circuit method is adopted to study microwave processes in an RF photoinjector, and the optimized coupling between the input mcirowave system and the RF cavity is theoretically obtained based on the micro-pulse properties of the RF phtoinjector. A CAEP RF photoinjector is theoretically analyzed, and the electron beam energy spread of micro-pulses induced by beam load is also investigated.
Approximate analytic solution of a class of atmosphere-ocean coupled oscillator mechanism for globe climate
Lin Wan-Tao, Mo Jia-Qi
2008, 57 (5): 2633-2637. doi: 10.7498/aps.57.2633
Abstract +
A box model of the interhemispheric thermohaline circulation (THC) in atmosphere-ocean for globe climate is considered. By using the homotopic mapping method, a class of simplified nonlinear model is studied, and the approximate solution is obtained. The homotopic mapping is an analytic method, which gives solutions that can be analytically operated subsequently to show diversified qualitative and quantitative behaviors of corresponding physical quantities.
The dual-resonance characteristic of coupled bistable system affected by two-frequency signal
Lin Min, Fang Li-Min, Zhu Ruo-Gu
2008, 57 (5): 2638-2642. doi: 10.7498/aps.57.2638
Abstract +
Two single bistable systems were constituted into a coupling system by means of nonlinear coupling. One of the bistable systems was considered as controlled system with fixed parameters, and the other as control system with adjustable parameters. Adjusting the coupling coefficients and parameters of the control system can produce stochastic resonance. With a single-frequency signal added to the control system, changing the signal frequency can produce the resonance. Due to the effect of coupling, the resonance of control system will affect the stochastic resonance of the controlled system, and the dual-resonance phenomenon happens in the coupled system, which realizes the usage of one resonance to influence another and make the stochastic resonance of controlled system more intense. This also has been verified using computer simulation.
Noether’s theory for Birkhoffian systems in the event space
Zhang Yi
2008, 57 (5): 2643-2648. doi: 10.7498/aps.57.2643
Abstract +
In this paper, the Noether symmetries and the Noether conserved quantities for Birkhoffian systems in the event space is studied. Firstly, the parametric equations for the Birkhoffian systems are established; secondly, the Noether's theorem and its inverse theorem for the systems are given, which are based upon the invariant properties of the Pfaffian action with respect to the action of the infinitesimal transformation; and finally, an examples is given to illustrate the application of the results.
Parametric equations and its first integrals for Birkhoffian systems in the event space
Zhang Yi
2008, 57 (5): 2649-2653. doi: 10.7498/aps.57.2649
Abstract +
In this paper, the dynamics of Birkhoffian systems in the event space is studied. The Pfaff-Birkhoff-d'Alembert principle and Birkhoff's parametric equations for the Birkhoffian systems are established in the event space of (2n+1) dimensions. The first integrals of the parametric equations and the conditions for their existence are presented.
The homotopy analysis method for solving a class of combustion models
Wu Qin-Kuan
2008, 57 (5): 2654-2657. doi: 10.7498/aps.57.2654
Abstract +
A type of nonlinear combustion model is studied. Using the homotopy analysis method, the approximation solution is obtained.
N-soliton interactions of Bose-Einstein condensates in external potentials
Zong Feng-De, Zhang Jie-Fang
2008, 57 (5): 2658-2668. doi: 10.7498/aps.57.2658
Abstract +
In this paper, a perturbed complex Toda chain has been employed to describe the adiabatic interactions in an N-soliton train of the Gross-Pitaevskii equation. Perturbations induced by weak quadratic and periodic external potentials are analytically and numerically studied. It is found that the perturbed complex Toda chain adequately models the N-soliton train dynamics for both types of potentials. As an application of the developed theory, we consider the dynamics of a train of matter-wave solitons confined in a quadratic trap and optical lattice, as well as tilted periodic potentials. In the last case, we demonstrate that there exist critical values of the strength of the linear or periodic potential for which one or more localized states can be extracted from a soliton train. In addition, some interesting results in the experiments and applications of the Bose-Einstein condensates are also obtained.
A periodic coupled quantum well transport
Yin Wen, Wang Hai-Xia
2008, 57 (5): 2669-2673. doi: 10.7498/aps.57.2669
Abstract +
Using the method developed by Gurvitz S.A for solving Shrodinger equations and numerical calculation, we investigate the driving frequency dependence of the current of periodic coupled quantum wells.The results indicate that the stable current increases with the driving frequency on condition of the driving frequency being smaller than the energy difference between wells. Otherwise, the stable current will decrease with increasing driving frequency. Therefore,the current of the system can be controlled by the driving frequency.
Coherent state of three-particle Calogero-Sutherland model
Li Wen-Bo, Li Mi-Shan, Li Ya-Ling, Wen Xiao-Yang, Yuan Guang-Jun, Zhang Chi, Yang Tao
2008, 57 (5): 2674-2679. doi: 10.7498/aps.57.2674
Abstract +
The three-particle CSM (Calogero-Sutherland model) is solved by the pseudo-angular-momentum method. Analytic expressions of the eigenstate and coherent states are obtained.
Quantum secret sharing of an arbitrary two-particle entangled state via non-maximally entangled channels
Liu Yu-Ling, Man Zhong-Xiao, Xia Yun-Jie
2008, 57 (5): 2680-2686. doi: 10.7498/aps.57.2680
Abstract +
In this paper, a quantum secret sharing scheme is proposed for an arbitrary two-particle entangled state among N agents. The scheme adopts the non-maximally entangled Bell states as quantum channels and the generalized Bell states as the measurement basis. By introducing an auxiliary particle and making selective measurement on it, the receiver can obtain the original quantum state with a probability less than unity.
The entanglement in one-dimensional random XY spin chain with Dzyaloshinskii-Moriya interaction
Shan Chuan-Jia, Cheng Wei-Wen, Liu Tang-Kun, Huang Yan-Xia, Li Hong
2008, 57 (5): 2687-2694. doi: 10.7498/aps.57.2687
Abstract +
In this paper, the entanglement in one-dimensional random XY spin system with Dzyaloshinskii-Moriya interaction is investigated, for which the impurities of exchange couplings and the external magnetic fields are considered as random Gaussian distribution variables. By solving the different spin-spin correlation functions and the average magnetization per spin, the concurrence is found. The results show that the Gaussian distribution and Dzyaloshinskii-Moriya interaction have considerable effect on the entanglement near particular locations of the system. Moreover, the entanglement can be controlled and enhanced by varying the distributions of the impurities, the strength of external magnetic field and Dzyaloshinskii-Moriya interaction.
The effect of Coulomb potential to the decoherence of the parabolic quantum dot qubit
Yin Ji-Wen, Yu Yi-Fu, Wang Zi-Wu, Xiao Jing-Lin
2008, 57 (5): 2695-2698. doi: 10.7498/aps.57.2695
Abstract +
On the condition of electric-LO phonon strong coupling in parabolic quantum dot, we obtained the eigenenergy of the ground state and the first excited state, the eigenfuctions of the ground state and the first excited state by using variational method of Pekar type. This system of quantum dot may be employed as a two-level quantum system-qubit. The phonon spontaneous emission causes the decoherence of the qubit. We discussed the relatoion between the decoherence time and the Coulomb binding parameter,the couping strength, the confinement length, and the conefficient dispersion.
Influences of time delay on logistic growth process driven by colored correlated noises
Han Li-Bo
2008, 57 (5): 2699-2703. doi: 10.7498/aps.57.2699
Abstract +
The small time-delay approach is applied to logistic growth model when time-delayed feedback and colored correlated noises are included in the system. The steady state probability distribution Pst(x) of the tumor cell number is obtained. It is found that a configuration transition of multiple peaks to a single peak occurs due to the variation of delay time τ. An extremum appears in the curves of the mean of the steady-state tumor cell number 〈x〉, the second moment 〈x2〉, and the normalized variance Var versus λ. The positions and the peak values of the extrema can be effected by the time delay.
Detecting faint variation in signal by synchronization of Duffing system
Qin Wei-Yang, Su Hao, Yang Yong-Feng
2008, 57 (5): 2704-2707. doi: 10.7498/aps.57.2704
Abstract +
For nonlinear Duffing system, a derived synchronization system is built and the method is proved. By the synchronization, the faint difference in stimulating signal of Duffing system can be detected. In simulation, when there occurs chaos in the original system, the responses of the original and derived system will exhibit synchronization for identical input signal and non-synchronization for different input signal. When the system is in quasi-periodic motion, the synchronization is still sensitive to the faint variation in the input signal. The simulation results prove the effectiveness of the method.
Chaotic time series prediction based on multi-kernel learning support vector regression
Zhang Jun-Feng, Hu Shou-Song
2008, 57 (5): 2708-2713. doi: 10.7498/aps.57.2708
Abstract +
Multi-kernel learning support vector regression (MKL-SVR) are proposed for chaotic time series prediction to solve the problems of kernel selection and hyper-parameter determination when using the standard SVR. The algorithm is realized through quadratic constrained quadratic programming (QCQP) in the hybrid kernel space, which not only reduces the number of support vectors, but also improves the prediction performance. Finally, it is applied to Mackey-Glass, Lorenz and Henon chaotic time series prediction. The results indicate that the proposed method can effectively increase the prediction precision, accelerate the convergency of cascade learning and enhance the generalization of prediction model.
Narrowband interference suppression in chaos-based communications based on set-membership estimation
Zhang Jia-Shu, Fan Yong-Quan
2008, 57 (5): 2714-2721. doi: 10.7498/aps.57.2714
Abstract +
This paper presents the set-membership estimation for narrowband interference (NBI) suppression in chaos-based communications. The proposed NBI suppression methods under known or unknown model parameters of interference signals are derived in terms of the optimal bounding ellipsoid criteria and the bounded property of chaotic carriers, respectively. Compared to the mean phase space volume (MPSV) based Kalman filtering and the recursive least square (RLS) algorithms, the proposed NBI suppression method estimates interference signals using only a few observations with the selective updating features, so that the computation is effectively reduced. Simulations results on AR and single tone interference suppression in chaotic parameter modulation (CPM) and differential chaotic shift keying (DCSK) communication systems show that the proposed NBI suppression methods can efficiently eliminate the narrowband interference signal in CPM and DCSK communication systems, and the computation is smaller than that of MPSV-based Kalman filtering and RLS algorithms.
The analysis of dynamic structure of silicon content in blast furnace hot metal
Zhao Min, Liu Xiang-Guan, Gao Chuan-Hou
2008, 57 (5): 2722-2727. doi: 10.7498/aps.57.2722
Abstract +
With Si time series of No.7 blast furnace (BF) at Han Iron and Steel Group Co. as sample space, the stationarity of Si time series is tested based on the number of reversed order. A statistical measure of dynamic closeness between two orbits is defined using correlation integral. Divide the Si series into equal-length windows, according to the calculation of the characterization between these windows, the dynamic abrupt changes in BF ironmaking process are detected. Finally the novel DVV (delay vector variance) method is used to examine the predictability of Si time series during the dynamic evolution.
Mechanism of period-doubling bifurcation in DCM DC-DC converter
Zhang Bo, Qiu Dong-Yuan, Wang Xue-Mei
2008, 57 (5): 2728-2736. doi: 10.7498/aps.57.2728
Abstract +
The period-doubling bifurcation in DC-DC converters has been investigated widely. However, the studies main focus on the models of bifurcations and the identification of strange attractors, the essential mechanism causing period-doubling bifurcation was not analyzed. This paper deduces mathematically the conditions of producing the period-doubling bifurcation in discontinuous current mode (DCM) Boost and Buck converters based on voltage feedback control. It exposes the mechanism of the period-doubling bifurcation in DC-DC converters and perfects the theoretical analysis method, puting forward an analytic method for studying the period-doubling bifurcation.
The collision of one keyed Hash function based on chaotic map and analysis
Wang Mei-Qin, Wang Ji-Zhi, Wang Ying-Long
2008, 57 (5): 2737-2742. doi: 10.7498/aps.57.2737
Abstract +
The collision of a keyed hash function based on chaotic map is pointed out. Its principle is analyzed in theory. The definition of the nonsingularity is presented based on analyzing digital discrete chaotic sequence. The necessary and sufficient conditions for the nonsingularity is deduced. The period of digital discrete chaotic sequence with variable parameter is discussed. The result shows that the singulartiy of chaotic sequence leads to the collision of the hash function. So the digital method of chaotic map must be chosen carefully to ensure the nonsingularity of chaotic sequence.
A method of detecting the unpredictability of chaotic signals based on periodic orbit statistics
Jin Jian-Xiu, Qiu Shui-Sheng, Xie Li-Ying, Feng Ming-Ku
2008, 57 (5): 2743-2749. doi: 10.7498/aps.57.2743
Abstract +
A method of detecting the unpredictability of chaotic signals is put forward based on periodic orbit statistics. Chaotic time sequences come from analog circuit and numerical simulation respectively. Hot saddle periodic orbits are found and its regression spectrum and regression frequency are investigated. The results show that the method is adequate for detecting the unpredictability of chaotic systems.
A digital watermarking algorithm based on chaos and fractional Fourier transformation
Zou Lu-Juan, Wang Bo, Feng Jiu-Chao
2008, 57 (5): 2750-2754. doi: 10.7498/aps.57.2750
Abstract +
Based on chaotic sequences and discrete fractional Fourier transform, a digital watermarking algorithm is proposed, and its resistance to attacks is simulated. The results show that the algorithm is easy to realize, and is robust to the attacks from JPEG compression, noise perturbation and filtering.
Parameter estimation for chaotic systems based on hybrid differential evolution algorithm
Wang Jun-Yan, Huang De-Xian
2008, 57 (5): 2755-2760. doi: 10.7498/aps.57.2755
Abstract +
Parameter estimation for chaotic systems is one of the important issues in chaotic control and synchronization. Through establishing an appropriate fitness function, the parameter estimation problem is formulated as a multi-dimensional functional optimization problem, which can be solved by using hybrid differential evolution (HDE) algorithm. A numerical simulation on the Lorenz system is conducted and the results demonstrate the effectiveness and robustness of the proposed algorithm, which is shown to be an effective method of parameter estimation for chaotic systems.
Multi-stable synchronization manifold in generalized synchronization of chaos
Yu Xiang, Zhu Shi-Jian, Liu Shu-Yong
2008, 57 (5): 2761-2769. doi: 10.7498/aps.57.2761
Abstract +
The phenomenon of multi-stable synchronization manifold (SM) in generalized synchronization (GS) refers to the coexistence of multiple chaotic response attractors, which all synchronize with the same driving dynamics in the sense of GS. In this paper, the multivalue characteristic of SM is investigated in the general sense on the basis of establishing the functional relationship between the driving and response systems. The stability of SM is studied and the conditions ensuring the existence of the multi-stable SM are deduced. A Genesio-Rssler coupled system and a coupled Duffing system with quadric and cubic nonlinear terms are analyzed as examples and the results show that there exist only one stable SM in the former, while the bifurcation evolves from bistable SM to single-stable SM with the increase of coupling strength in the latter.
Research of fine structure and universal constants of bifurcation in converters
Yang Ru, Chu Li-Li, Zhang Bo
2008, 57 (5): 2770-2778. doi: 10.7498/aps.57.2770
Abstract +
The fine structure and scaling invariability of bifurcation in converters is discussed. Universal constants of converters of one and two dimensions and chaos combination belts have been obtained by numerical simulation. Spectrum structure is used to estimate the system behavior and reveal the structure of solution in the converter. The structure of spectrum also validates the fine structure of bifurcation in the converter. Experiment results illustrate the process of bifurcation to chaos and validate the simulation results.
Synchronization of chaotic Liu system with uncertain parameters
Wang Hua, Han Zheng-Zhi, Zhang Wei, Xie Qi-Yue
2008, 57 (5): 2779-2783. doi: 10.7498/aps.57.2779
Abstract +
Based on the control Lyapunov function (CLF), a method of synchronizing chaotic Liu system with uncertain parameters is proposed. The feedback control law presented does not depend on the parameters but on the boundary of the parameters. It shows that the feedback is simple and robust. Simulation studies on Liu chaotic system also verify the effectiveness of the proposed scheme when the parameters vary largely.
Prediction of chaotic time series based on robust fuzzy clustering
Liu Fu-Cai, Zhang Yan-Liu, Chen Chao
2008, 57 (5): 2784-2790. doi: 10.7498/aps.57.2784
Abstract +
We propose a new method for fuzzy modeling based on a robust fuzzy-clustering algorithm. The induced local spatial similarity improved the system's robustness to noise and outsider and predicted the robustness of the modeling system. Starting from an initial fuzzy partition of input space by a nearest-neighbor clustering method to get the number of rules and the initial clustering center, we can compute and optimize the fuzzy membership and the clustering center with a robust fuzzy-clustering algorithm and get the high precision T-S model. The obtained parameters were identified by the least square method and further optimized by selective recursive least square. The proposed method was applied to simulations of chaotic Mackey-Glass time series modeling and prediction. The results demonstrated the robustness, effectiveness and practicability of the method.
Study on a class of chaotic systems with fractional order
Zhao Pin-Dong, Zhang Xiao-Dan
2008, 57 (5): 2791-2798. doi: 10.7498/aps.57.2791
Abstract +
In this paper, a class of chaotic systems with fractional order is generalized and their topological equivalence is proved. It indicates that the necessary condition for a system with fractional order to generate chaotic attractor is to maintain the stability of the equilibrium points of the system. Numerical simulation shows that, similar to chaotic systems with integer order, the class of chaotic systems with fractional order can also generate a couple of double-scroll chaotic attractors.
Chaotic properties of mechanically and electrically coupled nonlinear dynamical systems
Tian Rui-Lan, Wang Wei, Zhang Qi-Chang
2008, 57 (5): 2799-2804. doi: 10.7498/aps.57.2799
Abstract +
Based on the Silnikov criterion, the chaotic properties of mechanically and electrically coupled nonlinear dynamical systems were discussed. Using Cardano formula and series solution of differential equation, the eigenvalue problem and existence of homoclinic orbit were studied respectively. A rigorous proof of the existence of Silnikov-sense Smale horseshoe chaos was presented and some conditions leading to chaos were obtained. The space trajectory, Lyapunov exponent and Lyapunov dimension were investigated via numerical simulation, which showed that chaotic attractors exist in the non-linear dynamical systems.
Agreement of two entropy-based measures on quantifying the complexity of short-term heart rate variability signals from professional shooters
Zhuang Jian-Jun, Ning Xin-Bao, Yang Xi, Sun Biao, Zou Ming
2008, 57 (5): 2805-2811. doi: 10.7498/aps.57.2805
Abstract +
Using two entropy-based measures, namely the approximate entropy and sample entropy measures, we studied the complexity of heart rate variability signals obtained from professional shooting athletes in the situations of rest and practice match. The results demonstrate that the values of two measures calculated from the resting signals are both greater than those calculated from the training signals, which means that the signals collected during the match are more regular compared to those acquired in a resting state. For a better application of the two methods, we further investigated the influences of two factors: threshold r and data length N, on the performance of the algorithms. Although both approaches have the ability to discriminate the complexity of heart beat interval series from different states of the shooters, provided that the parameters required by the algorithms are chosen within a proper range, it still seems that sample entropy method is more appropriate in quantifying the short-term heart rate variability signals for shooting athletes, especially when the time series are only several hundred points long.
Adaptive projective synchronization and parameter identification of a class of delayed chaotic neural networks
Wang Xing-Yuan, Zhao Qun
2008, 57 (5): 2812-2818. doi: 10.7498/aps.57.2812
Abstract +
This paper deals with the adaptive projective synchronization problem of a class of delayed neural networks. Based on Lyapunov stability theory, a new control method is proposed to achieve parameter identification and projective synchronization simultaneously. Numerical simulations were conducted to verify the effectiveness of this method.
Studies on dual-core-bidirectional optical fiber chaotic secure communication system
Yan Sen-Lin
2008, 57 (5): 2819-2826. doi: 10.7498/aps.57.2819
Abstract +
A dual-core-bidirectional optical fiber chaotic secure communication system is proposed based on coupling-feedback synchronization of chaotic injected multi-quantum well (MQW) laser systems with fiber channels for optical fiber secure communications. A physical model of the system is built using dual-core optical fiber connecting the transmitter and receiver. Chaotic synchronization was theoretically and numerically studied and we found theoretically that self-phase modulation in the fiber would limit the chaotic synchronization. The nonlinear phase shift, power limit and propagation length are formulated. Chaotic synchronization of two long-distance fibers was numerically achieved, and synchronization time varying with fiber propagation length was numerically analysed. Optical fiber chaotic communications and their synchronization errors were numerically simulated in long-distance dual-core-bidirectiond optical fiber chaotic secure communications with an analog signal of modulation frequency 06 GHz, a digital signal of modulation rate 06 bit/s and a bit rate of 005 Gbit/s of chaos keying shift, respectively. The system bandwidth is also numerically analysed. The system has a good security capability of application in dual-core-bidirectional fiber secure communications.
Control of chaos in a delayed feedback semiconductor laser via dual-wedges
Yan Sen-Lin
2008, 57 (5): 2827-2831. doi: 10.7498/aps.57.2827
Abstract +
A method of controlling chaos is presented via dual-wedges in a delayed feedback semiconductor laser. The physical model of the laser dynamics is set up under the condition of the dual-wedges control. The optical-length of the transmission of feedback light in the external cavity can be governed by modulating the dual-wedges while the delay time and feedback intensity of the feedback light are varied. The dual-parameter chaos-control of the delay time and feedback intensity can be physically realized. The chaotic laser can be controlled in periodic states and its mean pulse power increased, as shown by numerical simulations.
Control of spiral wave and turbulence in the time-varied reaction-diffusion system
Yi Ming, Jin Wu-Yin, Ma Jun, Li Yan-Long
2008, 57 (5): 2832-2841. doi: 10.7498/aps.57.2832
Abstract +
We investigated the external electric field-induced transition of the spiral wave and turbulence in a class of time-varied reaction-diffusion systems. In our numerical simulation, a modified Fitzhugh-Nagumo model, which was used to describe the excitable and/or oscillatory media under appropriate parameters, was investigated. The effect induced by the random and/or other uncertain factors (for example, external and interior noise, gas pressure, temperature gradient and deformation of media etc.) was considered. The amplitude of the fluctuations of parameters was selected at appropriate values so that stable rotating spiral wave, meandering spiral wave and turbulence could be observed respectively. The external electric field was introduced into the media after a transient period allowing for parameter fluctuations. It was found that only the breakup of spiral wave was observed and the whole media could not reach homogeneous state when weak electric field and parameter fluctuation were used. It was confirmed that the breakup of spiral wave happens and then the whole media becomes stably homogeneous when appropriately strong intensity of external electric field is applied to the whole media together with the action of parameter fluctuation. The snapshots of the activator are used to investigate the transition of the patterns in the presence of external electric field and under parameter fluctuation, and relevant theoretical discussion is given in the precent paper.
Reducing frequency phenomenon in Buck converters with one cycle control
Wang Fa-Qiang, Zhang Hao, Ma Xi-Kui
2008, 57 (5): 2842-2848. doi: 10.7498/aps.57.2842
Abstract +
This paper deals with the reducing frequency phenomenon in Buck converters with one cycle control. The critical conditions of its occurrance and operation modes are derived. The results show that the reducing frequency phenomenon occurs because the output voltage of the integrator does not rise to the reference voltage Vref within n clock periods so that the integrator can not be reset in n clock periods but must be reset in the (n+1)th clock period. Furthermore, the converters are stable both in CCM and DCM when the reducing frequency phenomenon occurs. Meanwhile, the ratio of the intervals with the reference voltage Vref between CCM and DCM is held constant. In addition, the ripple of the output voltage is increasing with the decrease of the circuit operating frequency. Finally, these theoretical results are verified by the numerical simulation and circuit experiment.
Coherence resonance in neural networks with small-world connections
Zhou Xiao-Rong, Luo Xiao-Shu
2008, 57 (5): 2849-2853. doi: 10.7498/aps.57.2849
Abstract +
The nonlinear response of small-world biological nerve network in the Hodgkin-Huxley model in the absence of external periodic signal is studied. Simulation results show the ordered degree of spike sequence may reach a maximum when the strength of noise is a certain limited value. Namely, coherence resonance phenomenon is produced in small-world biology nerve network. The number of minima of coherence resonance coefficient cv is more than one. This indicates that coherence resonance may occur in different scales of networks.
Study of modular transfer function-based optieal low-pass filter evaluation model and experiment
Lin Bin, Cao Xiang-Qun, Chen Yu-Qing, Qi Xun-Jun
2008, 57 (5): 2854-2859. doi: 10.7498/aps.57.2854
Abstract +
To evaluate the performance of optical low pass filter (OLPF) accurately, a new 2D digital imaging system model including an OLPF was created for the first time using the modular transfer function (MTF). An evaluation function was also established based on this model. To manifest the model and its evaluation, three typical OLPFs were studied. The results show that the Δ value of each filter undergoes a slow and slight decrease and then rapidly increases when the ideal optical system cutoff frequency is increased. The optieal system embedded with the 2-chip-4-point type OLPF created a better image than those with the other two OLPF's when the F number is greater than 44; whereas the OLPF of 3-chip-8-point type worked best when the F number is lower than 44 When the F number of the optical system is 28, namely, with a spatial cutoff frequency of 649 lp/mm, the filter of 3-chip-8-point type performs better than that of the 2-chip-4-point and 3-chip-4-point types. The Δ value of the first filter is 283% and 375%, lower than that of the other two filters, respeatively. That is, the filter performance is 283% and 375% higher. Finally, spatial frequency test shows that the moiré fringe and false colors can be seen in the last two pictures, while in the first, these effects are well eliminated. The theoretical calculations agree with the experimental results.
Soft X-ray magmeto-optical Faraday rotation measurements with the multilayer polarizer
Zhao Jia, Wang Zhan-Shan, Zhu Jing-Tao, Zhang Zhong, Yan Fen, Cui Ming-Qi, Chen Kai, Sun Li-Juan, Xi Shi-Bo, Zhou Ke-Jin, Zheng Lei, Zhao Yi-Dong
2008, 57 (5): 2860-2865. doi: 10.7498/aps.57.2860
Abstract +
We measured magneto-optical (MO) Faraday rotation around the M2,3 edges (60—70 eV) of Ni film on 3W1B beam line of Beijing Synchrotron Radiation Facility (BSRF) in the soft X-ray region through a versatile polarimeter with mutilayer polarizers, which is mainly composed of polarizer, analyzer, sample frame, round NdFeB permanent-magnet and MCP detector. We used the reflective aperiodic molybdenum/silicon broadband multilayer polarizers as the polarizer and the analyzer in the versatile polarimeter, and obtained a series of Faraday rotation results in the 60—70 eV region. The results demonstrate that the Faraday rotation angles are obviously large around Ni M2,3 edges, the rotation angles are 179±019°(average rotation angle in parallel and antiparallel magnet fields) and -076±009°(average rotation angle in parallel and antiparallel magnet fields) at the energy 655 eV and 68 eV, respectively.
NUCLEAR PHYSICS

EDITOR'S SUGGESTION

Experimental study for neutron-rich exotic nuclei 17B
Hu Zheng-Guo, Wang Meng, Xu Hu-Shan, Sun Zhi-Yu, Wang Jian-Song, Xiao Guo-Qing, Zhan Wen-Long, Xiao Zhi-Gang, Zhang Hong-Bin, Zhao Tie-Cheng, Xu Zhi-Guo, Wang Yue, Mao Rui-Shi, Chen Ruo-Fu, Huang Tian-Heng, Gao Hui, Jia Fei, Fu Fen, Gao Qi, Han Jian-Long
2008, 57 (5): 2866-2870. doi: 10.7498/aps.57.2866
Abstract +
The total reaction cross section of 17B on C target has been measured by using the transmission method at the Radioactive Ion Beam Line in Lanzhou (RIBLL). Assuming 17B consisting of a core 15B plus two halo neutrons, the total cross section of 17B on C target was calculated with the zero-range Glauber model where Gaussian plus HO density distributions were used. It fitted the experimental data very well. A large diffusion was found about the density distribution of 17B. Based on the analysis, the two neutrons halo of 17B was confirmed.
The extraction method for trap parameters in 4H-SiC MESFETs
Che Yong, Lü Hong-Liang, Zhang Yi-Men, Zhang Yu-Ming, Wang Yue-Hu, Chen Liang
2008, 57 (5): 2871-2874. doi: 10.7498/aps.57.2871
Abstract +
The small signal equivalent circuit of SiC MESFETs has been studied and the parasitic and intrinsic elements have been extracted with both numerical and analytical methods. The trapping-emission mechanism is discussed in detail. The proposed model is valuable for the optimization of the device design and processing.
Kinetic theory of a novel THZ gyrotron with three-mirror quasi-optical cavity
Li Wen-Ping, Zhang Ya-Xin, Liu Sheng-Gang, Liu Da-Gang
2008, 57 (5): 2875-2881. doi: 10.7498/aps.57.2875
Abstract +
Based on the linear theory of gyrotron, and using the Laplace transformation and residue theorem, the kinetic theory of a novel gyrotron with three-mirror quasi-optical cavity is developed within the framework of the linearized Vlasov-Maxwell equations. The beam-wave interaction power, frequency shift and starting current have been derived and numerically calculated. The results indicate that this novel gyrotron has high interaction power when operating at high cyclotron harmonics, and has potential application in THZ band.
Gaussian pulse shaping of exponential decay signal based on wavelet analysis
Ji Shi-Yin, Chen Shi-Guo, Liu Wan-Song
2008, 57 (5): 2882-2887. doi: 10.7498/aps.57.2882
Abstract +
Gaussian pulse shaping of exponential decay signal based on wavelet analysis is reported. The peak height of Gaussian shaping signal represents the energy of radiation particle and the peak position represents the time of radiation event occurring, respectively. The experimental results with simulating and sampling signals show that the exponential decay signal has been shaped into Gaussian signal, which indicates that Gaussian pulse shaping based on wavelet analysis is valid. The result may serve as the theoretical basic for studying digital realization of Gaussian pulse shaping.
ATOMIC AND MOLECULAR PHYSICS
The effects of the Breit interaction on electron impact excitation cross sections of the 1s2s3S1 metastable level of He-like ions
Yang Ning-Xuan, Jiang Jun, Xie Lu-You, Dong Chen-Zhong
2008, 57 (5): 2888-2894. doi: 10.7498/aps.57.2888
Abstract +
The electron impact excitation(EIE) cross sections of He atom and He-like Fe24+, Xe52+ and U90+ ions from the metastable 1s2s3S1 to all of 1snl(n=2,3; l=s,p,d) states are calculated systematically by using the fully relativistic distorted-wave (RDWB) program developed by our group recently. The effects of the Breit interaction on the EIE cross sections of He-like isoelectronic sequences ions at different energies of incident electrons is studied, and some important conclusions are summarized, which can be extended to other highly charged ions. Also, comparison of the present calculations for 1s2s3S1→1s2p3P and 1s2s3S1→1s3s3S1 with the available experimental results gave good agreement.
The transformation of ultra-cold Rydberg atom to plasma
Zhao Jian-Ming, Zhang Lin-Jie, Li Chang-Yong, Jia Suo-Tang
2008, 57 (5): 2895-2898. doi: 10.7498/aps.57.2895
Abstract +
Ultra-cold Rydberg atoms are obtained using three-photon excitation in the Cs magneto-optical trap(MOT), and the signals of the plasma are measured through changing the interaction time. The spontaneous evolution and the ionization mechanism are investigated.
Relation of harmonic radiative energy and laser phase in high-order harmonic generation
Ge Yu-Cheng
2008, 57 (5): 2899-2905. doi: 10.7498/aps.57.2899
Abstract +
The behavior of an atom in strong laser field and the dynamic process of high-order harmonic generation (HHG) are analyzed with the quantum theory and saddle-point method. Within a laser optical cycle of a long duration laser, the relations between the radiative energy and the laser phase of HHG show a Gaussian-like distribution which peaks at 7180°. A parameterized formula is deduced to calculate the high harmonic emission duration and the bandwidth of the HHG energy-phase distribution. The peak position, maximum and the bandwidth of a selected energy-phase distribution pulse depend on the laser parameters. Calculations show that a pure single (double) energy-phase distribution pulse(s) can be generated by a 3-cycle laser with a carrier-envelope phase of 175° (105°). A single symmetric energy-phase distribution pulse peaks at the carrier phase of 5386° and spans 5334°. The double energy-phase distribution pulses separated by 17533° have the same height. They peak at -3151° and 14381°, and span 7219° and 7334°, respectively. These results may be useful for researches of ultra-short X-ray generation, pulse separation, measurement and its application.
The rotational excitation partial cross sections for the He-HI collisions
Yu Chun-Ri, Yin Xun-Chang, Wang Rong-Kai, Yang Xiang-Dong
2008, 57 (5): 2906-2912. doi: 10.7498/aps.57.2906
Abstract +
The close coupling approach is used to calculate the elastic and inelastic partial cross sections for collisions of helium atoms with hydrogen iodide molecules based on the intermolecular potential introduced in our previous research. The calculations are performed separately at the incident energies of 40, 75 and 100 meV. This study indicates that the excitation partial cross sections converge faster than the elastic partial cross section for each of the incident energies considered here. The excitation partial cross sections converge more rapidly for the higher excited states, and more slowly for the higher incident energies.
The transfer ionization mechanism in the low charge state ion-atom collisions
Liu Yu-Wen, Chen Xi-Meng, Shao Jian-Xiong, Ding Bao-Wei, Fu Hong-Bin, Cui Ying, Zhang Hong-Qiang, Lu Yan-Xia, Gao Zhi-Min, Du Juan, Chen Lin, Sun Guang-Zhi, Yin Yong-Zhi, Yu De-Yang, Cai Xiao-Hong
2008, 57 (5): 2913-2918. doi: 10.7498/aps.57.2913
Abstract +
In this work, the ionizations involving the charge transfer and single capture processes in low charge state ion-atom collisions in low-to-medium energy region, are investigated by the position sensitive and time-of-flight techniques. For a given charge state of the incoming projectiles, the dependence of the ratio RTS of the transfer ionization to the single capture changing with the projectile velocity is obtained, and the conclusion that the ionized electron in the transfer ionization process comes from the outermost sub-shell of the target atom is confirmed by comparing our theoretical results with the experimental data.
CLASSICAL AREA OF PHENOMENOLOGY
A new synthesis method for synthesizing on-axis flat-topped beams by using a defocusing telescope system
Zhao Bao-Yin, Lü Bai-Da
2008, 57 (5): 2919-2924. doi: 10.7498/aps.57.2919
Abstract +
A new method for synthesizing on-axis flat-topped beams by using a defocusing telescope system is proposed, where the flat-topped multi-Gaussian beam is chosen as the ideal beam. Within the framework of the paraxial approximation and based on the Collins diffraction integral formula, the analytical expressions for the on-axis field and incident field are derived and analyzed physically. The effect of beam order N, flat-top length parameter L, position of the flat-top centre zc and central longitudinal spatial frequency Sc on the on-axis intensity distribution is illustrated by numerical examples. A comparison of our results with the method for simulating the ideal beam by use of the rectangular function shows the advantages of our method.
A novel left-handed material with wire array in a ferrite-filled TE10 rectangular waveguide
Chu Qing-Xin, Gong Jian-Qiang
2008, 57 (5): 2925-2929. doi: 10.7498/aps.57.2925
Abstract +
A novel left-handed material is proposed, which is composed of a metallic wire array in an X-band TE10 rectangular waveguide filled with ferrite. The proposed structure is analyzed by using the transfer function matrix technique and with the full wave simulation tool Ansoft HFSS. The results show that there exist left-handed passband and backward wave propagation phenomenon for the proposed structure in the frequency band in which the effective permeability for the ferrite transversely magnetized is smaller than zero, and the frequency band can be tuned by adjusting the externally imposed magnetic field and the ferrimagnet's magnetization, so we believe such a structure should provide medium-loss and tunable left-handed passband.

EDITOR'S SUGGESTION

High-frequency analysis of scattering from coated targets with electrically large size in half space
Li Xiao-Feng, Xie Yong-Jun, Wang Peng, Yang Rui
2008, 57 (5): 2930-2935. doi: 10.7498/aps.57.2930
Abstract +
The high-frequency method for solving the scattering of electrically large coated targets in half space is presented in this paper. In order to consider the influence of environment, the half-space physico-optical integral equation is deduced by introducing the half-space Green's function into the physico-optical method. Combined with the graphical-electromagnetic computing method, the shadow regions are eliminated quickly and the geometry information is attained by reading the color and depth of each pixel. Meanwhile, we use the impedance boundary conditions to account for the target covered RAM in half space, and the radar cross section of coated targets can be exactly calculated in half space. The numerical results show that this method is efficient and accurate.
A direct discrete-finite-difference time-domain implementation of electromagnetic scattering by magnetized ferrite medium
Yang Li-Xia, Zhao Yue-Hua, Wang Gang, Yan Shu, Ge De-Biao
2008, 57 (5): 2936-2940. doi: 10.7498/aps.57.2936
Abstract +
Based on the constitutive relation between the magnetic permeability and magnetic flux density, the constitutive relation of magnetized ferrite medium in frequency domain is transformed to the time domain by using the corresponding relation between the time-differential operator /t and jω. And the constitutive relation including the time-differential operator /t in time domain is presented. By the introduction of a direct-discrete method, the time-differential operator /t is dispersed. Then direct discrete-finite-difference time-domain(DD-FDTD) iterative formula are derived in the discrete time domain. To exemplify the availability of the algorithm, the backscattering radar scattering section of a magnetized ferrite sphere is computed, and the numerical results are the same as the reference values, and show that the DD-FDTD method is correct and efficient.
Dependence of spectral width of TM-polarization lasing modes on pumping intensity in two-dimensional random media
Wang Ke-Jia, Zhang Qing-Quan, Lü Jian-Tao, Du Ze-Ming, Liu Jin-Song
2008, 57 (5): 2941-2945. doi: 10.7498/aps.57.2941
Abstract +
The spectral width of transverse magnetic (TM) lasing modes in two-dimensional random media is theoretically investigated by using the time-dependent theory. The evolution curve of the spectral width of TM-polarization modes versus the pump intensity is obtained from which one can calculate some characteristic parameters of the emission, e.g. the threshold. The results show that, from the view of spectral width, the emission of the TM-polarization lasing modes have better out-put property than that obtained previously with TE-polarization.
Influence of dopants on nonvolatile holographic storage in lithium niobate
Kong Yong-Fa, Chen Shao-Lin, Zhang Guo-Quan, Liu Xiang-Ming, Shen Yan, Xu Jing-Jun, Fu Bo, Xu Qing-Jun
2008, 57 (5): 2946-2951. doi: 10.7498/aps.57.2946
Abstract +
By studying the ultraviolet-red two-color holographic storage performances of Mg-, Zn- and In-doped lithium niobate crystals, we found that the response time of the two-color recording could be shortened by as much as 3 orders of magnitude compared to that of one-color recording, and the two-color recording sensitivity was improved significantly, which was measured to be 11 cm/J in the crystal doped with Mg of 5 mol.%. Nonvolatile holographic storage was achieved in the crystals with doping concentrations above the damage-resistant threshold value. However, gratings on the deep centers and the shallow centers were out of phase in Mg- or Zn-doped lithium niobate, while those in In-doped lithium niobate were in phase. We consider that different defects induced by different dopants are responsible for the observed results.
Modulation of the azimuth of polarization of reconstruction beam on the diffraction efficiency of anisotropic gratings recorded in bacteriorhodopsin films by two parallel linearly polarized beams
Yao Bao-Li, Wang Ying-Li, Lei Ming, Gao Peng, Han Jun-He, Chen Li-Ju
2008, 57 (5): 2952-2958. doi: 10.7498/aps.57.2952
Abstract +
When the linearly polarized object and reference beams with the same polarization direction are used for recording gratings in bacteriorhodopsin films, the azimuth of polarization of the reconstruction beam has an influence on the diffraction efficiency. By using Jones matrices to analyze this phenomenon, we find that the azimuth of polarization of the reconstruction beam makes a cosine modulation on the diffraction efficiency. The diffracted beam is linearly polarized only when the polarization of the reconstruction beam is parallel or perpendicular to that of the recording beams; otherwise, the diffracted beam becomes elliptically polarized. The azimuth of polarization of the reconstruction beam produces a positive cosine modulation on the peak diffraction efficiency, but a negative cosine modulation on the steady diffraction efficiency (with phase difference π). By adding auxiliary violet light during grating formation, the saturation of the grating can be restrained; as a result, the negative cosine modulation of the steady diffraction efficiency changes to the positive cosine modulation and also the steady diffraction efficiency is increased apparently.
The influence of injection current on transverse mode characteristics of vertical-cavity surface-emitting lasers
Yang Hao, Guo Xia, Guan Bao-Lu, Wang Tong-Xi, Shen Guang-Di
2008, 57 (5): 2959-2965. doi: 10.7498/aps.57.2959
Abstract +
The influence of transverse mode were researched with the injection current changing via experiments conducted with 980nm oxide-confined vertical cavity surface emitting lasers (VCSELs). Based on the spatio-temporal rate equation, the injection parameter dependence of the transverse mode characteristics of weak-index guiding VCSELs were theoretically researched by integrating the spatially dependent part. The result of the experiment indicated that the higher-order modes begin to emerge and exhibit strong competition with the injection current increased when the oxidized aperture was kept unchanged, and the distribution of the carrier transfers from the center to the edge. Furthermore, the main order becomes weaker because of the spatial hole burning. Compared with the appearance of higher-order modes with different oxidized aperture, the small injection aperture exhibits better single mode behavior.
Saturable absorption of Yb3+/Na+ codoped CaF2 crystals at 1050nm
Chai Lu, Yan Shi, Xue Ying-Hong, Liu Qing-Wen, Ge Wen-Qi, Wang Qing-Yue, Su Liang-Bi, Xu Xiao-Dong, Zhao Guang-Jun, Xu Jun
2008, 57 (5): 2966-2970. doi: 10.7498/aps.57.2966
Abstract +
The saturable absorption of Yb3+/Na+ codoped CaF2 crystals at 1050nm has been demonstrated by comparative experiments by inserting the novel Yb3+,Na+:CaF2 crystal with different doping concentrations into a Yb:YAG laser in stable continuous wave operation, which is the cause for the crystals working as the gain material to tend to self-Q-switching at 1050nm. The results show that the dominative element is Yb3+ rather than Na+ for saturable absorption action of the crystals. However, the effect of Q-switching by codoping Na+ into the CaF2 crystals can be greatly improved so that the Yb3+,Na+:CaF2 crystals with optimum concentration and doping ratio can be used as a Q-switching element at 1050nm.
Improving the stability of the Ti: sapphire oscillator
Chai Lu, Wang Qing-Yue, Cao Shi-Ying, Zhang Zhi-Gang
2008, 57 (5): 2971-2975. doi: 10.7498/aps.57.2971
Abstract +
Stability of the pulse intensity and timing jitter of the Ti: sapphire oscillator is analyzed in this paper. The stability, central wavelength and bandwidth of the pulse train from the Ti: sapphire oscillator with and without water cooling plate were experimentally compared. The results show that by introducing a water cooling plate, the stability of the Ti: sapphire oscillator can be improved.
Study on variations of stimulated Brillouin scattering parameters of mixed media with mixing ratio
Lü Zhi-Wei, Liu Shu-Jie, He Wei-Ming, Zhao Xiao-Yan, Zhang Wei, Hasi Wu-Li-Ji
2008, 57 (5): 2976-2980. doi: 10.7498/aps.57.2976
Abstract +
From the relation between the refractive index, viscosity, density, sound velocity and mixing ratio of mixed medium, we deduce the variation of SBS parameters, namely the Brillouin linewidth, phonon lifetime and gain coefficient, with mixing ratio. For the HT-70/FC-72 mixture, the variations of Brillouin linewidth, phonon lifetime and gain coefficient with mixing ratio are numerically simulated, and the variations of absorption coefficient and optic breakdown threshold with mixing ratio are measured in experiment. The results show that the SBS parameters exhibit a monotonic variation with mixing ratio without extrema. The use of mixed medium not only diversifies SBS medium but also optimizes the SBS system.
Bandwidth and gain of optical parametric chirped pulse amplification pumped by non-monochromatic light
Liu Hua-Gang, Zhang Ruo-Bing, Zhu Chen, Chai Lu, Wang Qing-Yue
2008, 57 (5): 2981-2986. doi: 10.7498/aps.57.2981
Abstract +
Laser pulse was decomposed into components of different frequencies using Fourier transform, and the numerical calculation model was built up for coupled equations of optical parametric amplification pumped by non-monochromatic light. Effects of non-monochromatic light on small signal gain, large signal gain and gain bandwidth of optical parametric amplification were investigated. Though non-monochromatic pump light decreases the gain of optical parametric process, it can improve the gain bandwidth. The larger the bandwidth of the pump light, the wider the gain bandwidth. Reasons for parametric gain decrease and gain bandwidth improvement were analyzed with respect to the phase mismatch and the parametric bandwidth.
Theoretical study on the first hyperpolarizabilities of stilbene derivatives
Wang Lei, Hu Hui-Fang, Wei Jian-Wei, Zeng Hui, Yu Ying-Ying, Wang Zhi-Yong, Zhang Li-Juan
2008, 57 (5): 2987-2993. doi: 10.7498/aps.57.2987
Abstract +
Static first hyperpolarizabilities of a series of stilbene derivatives are calculated at the CPHF/6-311G(d) level. the molecules which possess the electron push-pull pair and delocalized conjugated bridge structure have larger first hyperpolarizabilities because of the intramolecular charge transfer. The influence of position of the substitution, strength and number of donors and acceptors, and their coplanarity and asymmetry is discussed. The results indicate that the molecules may have larger first hyperpolarizabilities when the molecules have stronger and more donors and acceptors, large asymmetry of HOMO and LUMO, better coplanarity and higher accentricity. This work attemps at finding out the relationship between the structure and the property, thus providing theoretical basis for designing nonlinear optical molecules.
The improvement of fiber parametric amplifier pulse source via modulation of signal light
Yu Jin-Long, Hu Hao, Zhang Ai-Xu, Zhang Li-Tai, Wang Wen-Rui, Yang En-Ze, Jiang Yang
2008, 57 (5): 2994-3000. doi: 10.7498/aps.57.2994
Abstract +
Starting from the four-wave maxing coupled equations, we obtain the optical field expression of a fiber optical parametric amplifier (FOPA) pulse source. Furthermore, we analyze the evolvement of pulse frequency chirp and amplitude when the signal light is phase or intensity modulated. It is concluded that the pulse width has no significant improvement but the extinction ratio is improved when the signal light is intensity modulated; however, when the signal light is phase modulated, the pulse has enhanced positive linear frequency chirp, which means that we may obtain shorter pulse than that of the FOPA based pulse source which has the same pump power but without phase modulation on signal light. Finally, theexperimental results of 10 GHz operation demonstrated the validity of our theoretical analysis. Using the FOPA pulse source with 05 W average pump power and phase modulated signal light, the transform limited pulse is obtained which has 22 dB extinction ratio and 52 ps pulse width, which is 2 ps narrower than that without modulation.
Low temperature emission characteristics of an ytterbium sensitized erbium-doped tellurite glass
Zhang Xiang-Hua, Li Xu-Jie, Nie Qiu-Hua, Dai Shi-Xun, Xu Tie-Feng, Shen Xiang
2008, 57 (5): 3001-3005. doi: 10.7498/aps.57.3001
Abstract +
The 15 μm emission spectrum corresponding to the 4I13/2→4I15/2 transition and upconversion of Er3+ in tellurite glass in the temperature range from 8 to 300K is studied. The emission spectrum of Er3+: 4I13/2→4I15/2 transition is also analyzed using a peak-fit routine, and an equivalent four-level system is proposed to estimate the Stark splitting for the 4I15/2 and 4I13/2 levels of Er3+ in the tellurite glass. The results indicate that the 4I13/2→4I15/2 emission of Er3+ has considerable broadening due to a significant enhancement of the a' and b' emission peaks. Temperature-dependent FWHM are investigated, the results show that a monotonic increase of FWHM is observed for temperatures from 8 to 300K. Intense upconversion emission signals around 529, 545 and 669nm corresponding to the 2H11/2, 4S3/2, and 4F9/2 transitions, respectively, to the 4I15/2 ground state are generated and are measured as functions of temperature in the 8 to 300K range. The most remarkable result is observed in the green upconversion signal around 546 and 669nm which presented a maximum intensity enhancement of 2198 and 1556 times around 80K compared with that around 300K. Monotonic decrease is observed at temperatures above 80K. In the same temperature range the signal at 529nm diminishes to zero with lowering temperature.
Optimized design of phase plates for shaping partially coherent beams based on the adaptive genetic algorithm
Li Jian-Long, Lü Bai-Da
2008, 57 (5): 3006-3010. doi: 10.7498/aps.57.3006
Abstract +
Based on the adaptive genetic algorithm,the optimized design of phase plates for shaping partially coherent beams is performed. Taking the Gaussian Schell-mode beam as an example,the analytical expression for the far-field intensity is derived and the phase plate capable of transforming GSM beams to flat-topped ones is optimized. The effect of spatial coherence on the beam shaping is illustrated by a numerial example. Comparison of the results with the previous work shows the advantages of the adaptive genetic algorithm in shaping partially coherenct beams.
A new analysis method of multi-cladding photonic crystal fibers
Wei Dong-Bin, Zhao Xing-Tao, Yuan Jin-Hui, Meng Jia, Wang Hai-Yun, Zhou Gui-Yao, Hou Lan-Tian
2008, 57 (5): 3011-3015. doi: 10.7498/aps.57.3011
Abstract +
The conventional effective index method can only simulate the photonic crystal fibers with single cladding structure. To solve the problem,an improved effective index method is proposed in this paper. It calculates the propagation properties of multi-cladding photonic crystal fibers. The indices and total dispersions of the guided modes of three-cladding photonic crystal fibers are investigated by this method. The results agree closely with those of the multipole method. Improved effective index method not only extends the application of conventional effective index method,but also provides theoretical support for analyzing and designing multi-cladding photonic crystal fibers with different propagation characteristics.
Study on quantum cryptography using orbital angular momentum states of photons
Su Zhi-Kun, Wang Fa-Qiang, Lu Yi-Qun, Jin Rui-Bo, Liang Rui-Sheng, Liu Song-Hao
2008, 57 (5): 3016-3021. doi: 10.7498/aps.57.3016
Abstract +
We present a simple quantum cryptographic scheme that encodes information in two orthogonal orbital angular momentum states. The states used in this scheme are invariant under rotations of the propagation direction,making this implementation independent of the alignment between the reference frames of Alice and Bob. Besides,since the two orbital angular momentum states are orthogonal,100% use of the photons is attained,which increases the key generation rate of the protocol.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Study on the optical and electrical properties of plasma for the deposition of microcrystalline silicon
Zhang Fa-Rong, Zhang Xiao-Dan, Zhao Ying, Zhao Jing, Amanatides E., Mataras D.
2008, 57 (5): 3022-3026. doi: 10.7498/aps.57.3022
Abstract +
Optical emission spectroscopy and Fourier transform power and impedance analysis have been used to investigate the effects of substrate bias and glow discharge on the plasma optical and electrical properties for the deposition of microcrystalline silicon. Results show that the Hα emission intensity distribution has the same tendency under bias AC,floating and -DC +AC, and their mean sheath lengths are almost located at the same position of the electrode gap. Compared to the above three bias states,Hα emission intensity increases sharply and double layers appear under +DC+AC bias and grounded conditions. Increasing of glow discharge power leads to the rise of Hα emission intensity,both the resistance and reactance decrease,and the plasma becomes more capacitive.
Design and analysis of the Z-pinch loads on the PTS facility
Ding Ning, Zhang Yang, Ning Cheng, Shu Xiao-Jian, Xiao De-Long
2008, 57 (5): 3027-3037. doi: 10.7498/aps.57.3027
Abstract +
In this paper,a method for designing and optimizing the wire-array loads used on the PTS facility is presented. Both ZP-0D code (shell model) and MARED-1D code (MHD model) are used for the simulation. By comparing results from each code,the characteristics of the Z-pinch implosion plasma driven by the PTS facility are investigated,and the load parameters are optimized. It is found that,a 15nH concentrator inductance is efficient for PTS facility to work at load currents up to 10MA. And an optimized tungsten wire-array load is able to produce an X-ray radiation with peak power up to 100TW and a highest efficiency of conversion for the wall-plug power of about 10%. By further investigation and comparison with experimental data,we suppose that the PTS facility will have similar X-ray radiation productivity as the Saturn facility operating in the long-pulse mode.
Second harmonic generation by the Kelvin-Helmholtz instability for two-dimensional incompressible fluid
Ye Wen-Hua, Wang Li-Feng, Li Ying-Jun
2008, 57 (5): 3038-3043. doi: 10.7498/aps.57.3038
Abstract +
A model of second harmonic generation by Kelvin-Helmholtz (KH) instability is presented. Weakly nonlinear theoretical results of the growth of the second harmonic agree well with the results of the LARED-S code. Nonlinear threshold of the KH instability for the single mode perturbation is determined by two-dimensional simulation.
Study on the focus performance of micro-focus Fresnel zone plate
Dong Jian-Jun, Cao Lei-Feng, Chen Ming, Du Hua-Bing, Xie Chang-Qing
2008, 57 (5): 3044-3047. doi: 10.7498/aps.57.3044
Abstract +
The performance of micro-focus Fresnel zone plate(MFZP) with the outermost width of 150nm is tested using the Ti spectral line. Experimental data indicates that the image of pinhole with diameter of 125μm fully responses to a pixel of the X-ray CCD camera. Furthermore,the X-ray focal spot is tested with a magnification of 66 by using laser striking the Ti planar target. The MFZP's point spread function is simulated with the integral formula of Fresnel-Kirchhoff diffraction. The simulated results indicate that the MFZP strongly focuses at double foci. The same results are obtained when the object distance and image distance change but keeping the relation of the lens unchanged. The simulation and the experiment indicate that MFZP can be applied to point-to-point imaging of X-ray to realize high spatial resolution imaging for the laser plasmas.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Numerical simulation of microstructure evolution during directional solidification of Ti-45at.%Al alloy
Guo Jing-Jie, Li Bang-Sheng, Wang Kuang-Fei, Mi Guo-Fa, Fu Heng-Zhi
2008, 57 (5): 3048-3058. doi: 10.7498/aps.57.3048
Abstract +
The microstructural evolution of Ti-45at.%Al alloy during directional solidification was simulated by applying a solute diffusion controlled solidification model,and the results have showed that under high thermal gradient the stable primary spacing can be adjusted by branching or competitive growth,irrelevant of the initial seed spacing. In addition,under a given pulling speed,increasing thermal gradient decreases primary cell/dendrite spacing,and under a given thermal gradient,increasing pulling velocity,we have observed a cell/dendrite transition region consisting of cells and dendrites,and which varies with the thermal gradient in a contradicting way,i.e. increasing the thermal gradient leading to the decrease of the range of the transition region. The simulated results agree reasonably well with experiment results.
Conductance enhancement phenomenon of graphene ribbons on highly oriented pyrolytic graphite surfaces studied by scanning probe microscopy
Wang Qi, Zhao Hua-Bo, Zhang Zhao-Hui
2008, 57 (5): 3059-3063. doi: 10.7498/aps.57.3059
Abstract +
Based on comparative observations with the conducting atomic force microscope and the scanning tunneling microscope,conductance enhancement phenomenon of graphene ribbons on highly oriented pyrolytic graphite surfaces has been studied. According to measured data of local resistance on the samples,the phenomenon is attributed to the state of point contact of the conducting tip on the sample surface. It was demonstrated that the conductance of the point contact is proportional to the local density of electrons in the contacting surface area,so we conclude that the conductance enhancement phenomenon results from the high density of electrons on the graphene ribbons.
Prevention of misfit dislocations by using nano pillar crystal array substrates
Zhou Nai-Gen, Zhou Lang
2008, 57 (5): 3064-3070. doi: 10.7498/aps.57.3064
Abstract +
Three-dimensional molecular dynamics simulations of epitaxial growth of aluminum film on substrates of nano pillar crystal array have been carried out. The embedded atom method (EAM) potential was employed for computing atomic interaction in aluminum. The results show that,the nano pillar crystal array substrate can release the misfit strain in the epitaxial film without forming any misfit dislocations,achieving a high quality epitaxial crystal film. However,two conditions must be met: 1) the cross sectional size of pillar crystal should be larger than the critical size of thermal stability,which is 19nm for aluminum at 700K;2) the height-space interval ratio of pillar crystals should be higher than 076. The latter ensures that the epitaxial layers on the neighboring pillar crystals can bridge with each other,and form a continuous film free of misfit dislocations.
Experimental investigation of superhydrophobic properties of the surface constructed by nanoparticles
Gu Chun-Yuan, Di Qin-Feng, Shi Li-Yi, Wu Fei, Wang Wen-Chang, Yu Zu-Bin
2008, 57 (5): 3071-3076. doi: 10.7498/aps.57.3071
Abstract +
Two kinds of micro- and nano-structural surfaces were constructed with hydrophobic nanoparticles(HNPs)directly. One of the surfaces was formed by compressing the nano powder to a smooth slice, the other was made by adsorbing the nanoparticles on the surface of rock wafer. The contact angles between water drops and the surfaces were measured and the rolling process of a water drop on the nanoparticles-adsorbed rock surface was pictured. The scanning electron microscope(SEM) was used to observe the microstructure of these surfaces also. The results show that the inorganic nanoparticles modified by weak hydrophobic material could have strong hydrophobic property, even though it was strongly hydrophibic initially. The measured contact angles of water drop on the nanoparticle-adsorbed rock surface are always greater than 120°and the rolling angles are less than 7°. These data means that these surfaces are superhydrophobic apparently. The SEM pictures show that these surfaces are air-solid compound interfaces with irregular micro- and nano-structure. It is these special structures that lead to the formation of superhydrophobic surfaces, which are in agreement with the Cassie-Baxter model.
Anharmonic phonon coupling and phonon confinement in nanocrystalline anatase TiO2
Zhao Jian-Hua, Chen Bo, Wang De-Liang
2008, 57 (5): 3077-3084. doi: 10.7498/aps.57.3077
Abstract +
A temperature-dependent Raman scattering study of the Eg(1) mode was carried out at 83 to 723K for nanocrystalline anatase TiO2 with different sizes of 194,86 and 56nm. By means of a combined model of anharmonic coupling and phonon confinement,the Eg(1) Raman spectra were fitted and calculated. The results show that,the temperature-dependent lattice vibration fundamentals are essentially the same for the three samples. The blue shift of Raman frequencies mainly comes from the contribution of three-phonon processes. In order to get good fittings,both the three- and four-phonon processes need to be considered. With increasing temperature,the four-phonon process becomes more important and counteracts the effect of the three-phonon process. The anharmonic-decay-related phonon lifetime increases as nanocrystalline size decreases,and the smaller nanoparticles have slower anharmonic decay. At low temperatures,the phonon confinement is responsible for a much shorter phonon lifetime for the 56-nm nanocrystals. The phonon confinement induces a blue shift of the Eg(1) mode and an asymmetrical broadening at high frequencies. It has a relatively larger effect on the linewidth broadening than on the peak shift.
The optical and nonlinear optical properties of Au:TiO2 and Au:Al2O3 composite films
Qian Shi-Xiong, Zhu Bao-Hua, Wang Fang-Fang, Zhang Kun, Gu Yu-Zong, Guo Li-Jun, Ma Guo-Hong
2008, 57 (5): 3085-3092. doi: 10.7498/aps.57.3085
Abstract +
On the basis of measurement and theoretical analysis,optical and nonlinear optical properties of the Au:TiO2 and Au:Al2O3 composite films with different Au nanoparticle size and different substrates were investigated. The relationship between the Au nanoparticle size and substrates and the surface plasmon resonance (SPR) of Au composite films were characterized by UV-VIS-NIR spectroscopy,and the dependence of third-order nonlinear susceptibility of the composite films on Au nanoparticle size and substrates was investigated by picosecond Z-scan technique with different exciting wavelengths (532nm and 1064nm). The analysis of optical properties of these films was carried out using the theories of surface plasmon resonance and localized field enhancement,respectively. The experimental and theoretical results revealed the dependence of third-order nonlinear susceptibilities χ(3) on Au nanoparticle size and substrates. For Au nanoparticle of size around 35nm embedded in TiO2 substrate with larger permittivity and the exciting wavelength at 532nm close to the surface plasmon resonance (618nm—632nm),the third-order nonlinear susceptibility χ(3) showed a maximum value of 25×10-9esu.
Staging effects on the structural and energetic properties of fast ionic conductor LixTiS2
Jiang En-Yong, Song Qing-Gong, Kang Jian-Hai
2008, 57 (5): 3093-3099. doi: 10.7498/aps.57.3093
Abstract +
A series of cell models for stage-2 ordered LixTiS2(x=1/8,1/6,1/4,1/3,3/8,1/2)system were constructed according to concentration-wave theory. Geometry optimizations and total energy computations were carried out for the stage-2 ordered systems and stage-1 ordered LixTiS2(x=0,1/4,1/3,1/2,2/3,3/4,1)system by plane-wave pseudopotential method. The results of stage-2 ordered systems were compared with that of stage-1 ordered systems. It turns out that there is a similar increment tendency in lattice parameters c(d) of stage-2 cell and 2c0(d) of stage-1 cell. Furthermore,there are extra expansions of c1(d),i.e. the space between two sandwiches with intercalated ions in stage-2 system,compared with c0(d),i.e. the space between two sandwiches in stage-1 system,and the corresponding c2(d),i.e. the space between two sandwiches without intercalated ions in stage-2 system, is compressed. The extrc expansion of c1(d) is complementary to the compression of c2(d) to a certain extent. Staging has remarkable effect on the atomic structure of TiS2 sandwiches. The formation energy of stage-2 ordered Li1/2TiS2 is distinctly higher than that of stage-1 ordered Li1/2TiS2,indicating that the latter is more stable than the former,which is well in accordance with the experimental results reported. The lower formation energy of stage-2 ordered Li1/4TiS2,compared with stage-1 ordered Li1/4TiS2,predicts a new ordered structure.
Characteristics of acoustic phonon transport and thermal conductance in quasi-one-dimensional quantum waveguides with semi-circular-arc cavity
Yao Ling-Jiang, Wang Ling-Ling
2008, 57 (5): 3100-3106. doi: 10.7498/aps.57.3100
Abstract +
By using the scattering matrix method,the transmission coefficient and thermal conductance of acoustic phonon through a quantum waveguide with semi-circular-arc cavity under both stress-free and hard-wall boundary conditions at low temperatures are studied. The results show that the transmission spectra and thermal conductance exhibit different characteristics under two different boundary conditions. Under the stress-free boundary condition,the universal quantum thermal conductance can be observed regardless of the geometry details in the limit T→0. The quantized plateau is observed only on assuming that the quantum wire is perfect (uniform). For quantum structures with semi-circular-arc cavity,the plateau is destroyed due to the additional scattering induced by the nonuniform waveguide widths to the phonon. When the hard-wall boundary condition is applied,the universal quantum thermal conductance disappears. The thermal conductance increases with the increase of temperature. Moreover,it is found that both the transmission coefficient and thermal conductance can be adjusted by changing the radius of the semi-circular-arc cavity.
The effect of infrared laser-induced micro/nano photothermal expansion and the novel method of photothermal actuation
Zhang Dong-Xian, Liu Chao, Zhang Hai-Jun
2008, 57 (5): 3107-3112. doi: 10.7498/aps.57.3107
Abstract +
This paper presents a novel asymmetric microactuator based on photo-thermal expansion. It has an asymmetric structure consisting of two thin expansion arms with different widths. When a beam of infrared laser irradiates the arms,the different increases in temperature and photo-thermal expansion controlled by the different rates of specific surface area causes a magnified lateral deflection. In the paper,the thermodynamic model is introduced,and the computing formula of lateral deflection is given. A prototype microactuator of 750μm length has been manufactured by using the excimer laser micromaching system Optec Promaster with an infrared laser diode (998nm) as the external power source to activate the microactuator. Then we carried out feasibility experiments by using a monitored control system made by our laboratory,and measured the relationship between the lateral deflection and laser power. The experiment results demonstrate that the deflection of the microactuator reached 258μm at 16mW infrared laser power. The photo-thermal microactuator has the advantages of simple structure,adjustable deflection,no electromagnetic interference,easy integrating and remote controlling. It will be quite useful for applications in the fields of micro/nano-technology and micro-electro-mechanical systems (MEMS).
Spectroscopic ellipsometer (SE) studies of a novel cyanine dye in Langmuir-Blodgett films
Zeng Hao, Gao Feng, Ma Shi-Hong
2008, 57 (5): 3113-3119. doi: 10.7498/aps.57.3113
Abstract +
The optical properties of the HQ Langmuir-Blodgett films (Y-type) have been studied in the range of ultraviolet-visible light (λ=2755—8266nm) by using the spectroscopic ellipsometer. The high absorption of the LB films in different frequency ranges have been discussed. We have also carried out the theoretical computation and numerical value fitting by using the Lorentz oscillator model for the films and the fitting results were in agreement with the experiment data.
Theoretical study of native point defects on anatase TiO2 (101) surface
Ma Xin-Guo, Jiang Jian-Jun, Liang Pei
2008, 57 (5): 3120-3125. doi: 10.7498/aps.57.3120
Abstract +
First-principles plane-wave pseudopotential calculations were performed to study the energetics and the geometical structures of intrinsic vacancies and interstitials on the anatase TiO2 (101) crystal surface. Firstly,we analyzed the effects of point defects on the geometrical structures. For the O vacancy,all the nearest-neighbor Ti atoms move away from the vacancy toward the other O neighborhood. As Ti1 or Ti2 is missing here,O1 atom spontaneously and strongly binds with nearest-neighbor O on the lattice site to form an O2 molecule. The results also show that interstitial Tii2 affects little host lattice and the interstitial Oi would spontaneously bind to lattice oxygen. By investigating the calculated defect formation energies,we found that under the O-rich condition,the VTi1 and Oi formation are favorable,however,under the Ti-rich condition,although the point defects of Tii2 and VO1 easily appear,the formation energy of the Tii2 is lower than that of the VO1. Finally,to determine the relative stability of the point defects,the formation enthalpies of several point defects were considered.
Study on thermal conductivity of hydrogenated amorphous silicon films
Li Shi-Bin, Wu Zhi-Ming, Yuan Kai, Liao Nai-Man, Li Wei, Jiang Ya-Dong
2008, 57 (5): 3126-3131. doi: 10.7498/aps.57.3126
Abstract +
The thermal conductivity of hydrogenated amorphous silicon (a-Si:H) film was measured using platinum metal as heating resistance. The films are prepared by plasma enhanced chemical vapor deposition (PECVD) and the thickness of them is in the range of 300—370nm. The dependence of thermal conductivity of the films on substrate temperature was studied. The influence of substrate temperature on the growth rate of a-Si:H films was obtained by spectra ellipsometer (SE). Fourier-transform infrared spectrometer (FTIR) was used to characterize the infrared spectra of films deposited on KBr substrate. The thermal absorption duc to vibrational mode of Si-H bond decrease the thermal conductivity of the films. Kinetic theory was used to analyze the result that the thermal conductivity of the films increases with the increasing of mean temperature. The effects of phonon propagation and free electrons displacement on thermal conductivity was also compared.
Dependence of growth and property of YBa2Cu3O7-x coated conductors on the thickness of CeO2 buffer layer
Wang Jing, Liu Jun, Yu Ben-Fang, Guo Dong-Yun, Li Mei-Ya, Zhao Xing-Zhong
2008, 57 (5): 3132-3137. doi: 10.7498/aps.57.3132
Abstract +
Biaxially textured MgO templates were grown on un-textured metal substrates by inclined-substrate-deposition and YBa2Cu3O7-x films were epitaxially grown on these substrates by pulsed laser deposition. Yttria-stablized-zirconia and CeO2 were deposited in turn as buffer layers prior to YBa2Cu3O7-x growth. The biaxial alignment features of the films were examined by X-ray diffraction 2θ-scan,pole-figure,-scan and rocking curve of Ω angles. The Raman spectroscopy,scanning electron microscopy and atomic force microscopy were used to characterize the orientation order,morphology and surface roughness of the YBa2Cu3O7-x films,respectively. The influence of the thickness of CeO2 on the properties of the YBa2Cu3O7-x films were investigated and the singnificant and unique dependence of the properties of YBa2Cu3O7-x films on the thickness of CeO2 were revealed. The possible mechanisms for this dependence were discussed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
First principles study of In-N codoped ZnO
Chen Kun, Fan Guang-Han, Zhang Yong, Ding Shao-Feng
2008, 57 (5): 3138-3147. doi: 10.7498/aps.57.3138
Abstract +
The electronic structure of pure N-doped and In-N codoped wurtzite ZnO has been calculated by using first-principles ultra-soft pseudo-potential approach of the plane wave based upon the density functional theory,and the structure change,bandstructure,density of states,difference charge density and the influence of In-N codoped wurtzite ZnO by H atom were studied. The calculation results revealed that N-doped wurtzite ZnO caused formation of deep N acceptor levels in the band gap and the carriers (hole) were localized near the top of the valence band. But the codoping calculation revealed that the acceptor level shifted toward the lower-energy region and shallow acceptor level were fomed,which was broadened and showed delocalizing characters, owing to which the concentration of impurities and the stability of the system were enhanced. Our conclusions accord with the results of experiments, which confirms the fact that In-N codoping in wurtzite ZnO helps the formation of p-type ZnO. In addition, it was also pointed out that the presence of H atom reduces the efficiency of doping markelly,which should be avoided as much as possible.
Effect of side groups on the electronic transport properties of molecular devices
Xia Cai-Juan, Fang Chang-Feng, Hu Gui-Chao, Li Dong-Mei, Xie Shi-Jie, Zhao Ming-Wen, Liu De-Sheng
2008, 57 (5): 3148-3154. doi: 10.7498/aps.57.3148
Abstract +
Basing on ab initio methods and nonequilibrium Green's function(NEGF) theory, we have investigated the electronic transport properties of 4-4′-dimercaptodibenzene molecular which have been functionalized with different side groups. Numerical results show that the same side group on different site does not strongly affect the resonances responsible for current flow through the molecular. But different side groups on the same site will have a stronger effect on the energetics of the molecular device than on the orbitals responsible for current transport. So functionalization has a significant effect on the interactions within the molecular, and the molecular with NO2 side group exhibit local minima associated with twisted conformations of the molecular device which can induce the molecular memory effect.
First principle study on the electron life span of degenerate anatase phase TiO2 semi-conductor with high concentration of oxygen vacancies
Hou Qing-Yu, Zhang Yue, Zhang Tao
2008, 57 (5): 3155-3159. doi: 10.7498/aps.57.3155
Abstract +
Plane wave ultrasoft pseudopotential technique based on the density functional theory was used to study the effect of high concentration of oxygen vacancies on the electron life span. Using first-principle theory, the structure of anatase TiO2 was optimized, then the state density was calculated. The result showed that at a constant temperature and with high oxygen vacancy concentration, the life span of electrons in anatase TiO2 declines with the increase of the O vacancy concentration, while the electron concentration has no effect on the electron lifes pan. Meanwhile, the Mott phase transformation takes place when the concentration of oxygen vacancies in anatase TiO2 is high.
Study of friction between hydrocarboxylic acid Langmuir-Blodgett films and its mechanism using molecular dynamics simulation
Zhang Zhao-Hui, Han Kui, Li Hai-Peng, Tang Gang, Wu Yu-Xi, Wang Hong-Tao, Bai Lei
2008, 57 (5): 3160-3165. doi: 10.7498/aps.57.3160
Abstract +
Molecular dynamics simulation has been used to study the friction and structure mechanism of Langmuir-Blodgett films of hydrocarboxylic acid (C15H31COOH) deposited on the SiO2 substrates at different sliding velocities. The results show that, for a certain monolayer, the shear pressure between the monolayers increases when the sliding speed is below 60m/s and decreases when the sliding speed exceeds 60m/s. The molecular tilt angle decreases as the velocity increases. The molecular clusters formed in the monolayers by the hydrogen-bond caused the long shear periods, but there is no hydrogen-bond between the monolayers.
Role of contacts in the conherent transport
Zhang Li, Yu Ya-Bin, Cai Meng-Qiu, Liu Yi-Xing, Quan Jun
2008, 57 (5): 3166-3170. doi: 10.7498/aps.57.3166
Abstract +
In order to study the role of contacts in the coherent transport of mesoscopic structure systems, a 2D-1D-2D model of nano-sized single-barrier system is considered, which includes a single-barrier structure conductor with two reservoirs. Basing on the scattering-matrix method and the Thomas-Fermi approximation, we have calculated the transmission probability and the distribution of internal potential when a dc voltage is applied to the system. The results show that: (1) the contacts can produce significant effects on the transmission probability; (2) the behaviors of conductance and the distribution of internal potential differ from the usual transport conductance give by the Kirchhoff's laws. Therefore we conclude that since contacts and the mesocopic systems are quantum coherent, the role of contacts is important for in-depth investigation of the transport in mesoscopic systems.
Analysis of structure parameters and current conduction mechanisms of AlGaN/GaN Schottky contacts
Wang Xin-Juan, Zhang Jin-Feng, Zhang Jin-Cheng, Hao Yue
2008, 57 (5): 3171-3175. doi: 10.7498/aps.57.3171
Abstract +
An investigation on the current conduction mechanisms of AlGaN/GaN Schottky contacts is presented in this paper. The ideality factor and the barrier height of Schottky contact on AlGaN/GaN heterostructure are calculated by I-V measurement in a wide temperature range. By subtraction of generation-recombination, tunneling and leakage currents from the total current, the “pure" Schottky barrier height can be evaluated with higher physical relevance. After analyzing the variational rules of Schottky contact characteristics on AlGaN/GaN heterostructure at 300—550K, it is concluded that surface leakage current plays an insignificant role in producing the gate leakage current of AlGaN/GaN HEMT.
Change in stress of GaN light-emitting diode films during the process of transferring the film from the Si(111) growth substrate to new substrate
Xiong Chuan-Bing, Jiang Feng-Yi, Fang Wen-Qing, Wang Li, Mo Chun-Lan
2008, 57 (5): 3176-3181. doi: 10.7498/aps.57.3176
Abstract +
InGaN multiple-quantum-well(MQW) light-emitting diode(LED) thin films were successfully transferred from the original Si(111) substrate to new Si substrate, and then the vertical structure LEDs were fabricated. After the original substrate removal, the residual tensile stress in GaN layer of the transfferred film is partially relaxed, while the compressive stress in InGaN well layer is increased. When the buffer layer of the transferred LED film was eliminated, the tensile stress in GaN layer was shown to increase. However, the compressive stress in InGaN well layer was kept unvaried. The performance of the vertical LEDs was significantly improved compared with the lateral LEDs.
Electronic Raman scattering and the second-order Raman spectra of the n-type SiC
Han Ru, Yang Yin-Tang, Chai Chang-Chun
2008, 57 (5): 3182-3187. doi: 10.7498/aps.57.3182
Abstract +
The Raman scattering spectra of the nitrogen doped n-SiC is studied. The theoretical line shape analysis indicates that, compared with 4H-SiC, the shift of the LO phonon-plasma coupled mode in 6H-SiC with free carrier concentration is smaller. From the electronic Raman spectra, which were obtained with laser excitation at 5145nm, there are four spectral lines in 6H-SiC and two lines in 4H-SiC, which correspond to the 1s(A1) to 1s(E) valley orbit transitions at the inequivalent k site. The explanation of the high-frequency signals of 6303 and 635 cm-1 is that they are velated with transitions at active deep level of defect. Finally, the second-order Raman features of 6H- and 4H-SiC are identified using the selection rules for second-order scattering in wurtzite structure.
The study of ZnO varistor doped with ferromagnetic manganese oxide
Yang Xin-Sheng, Zhao Yong
2008, 57 (5): 3188-3192. doi: 10.7498/aps.57.3188
Abstract +
ZnO varistor doped with ferromagnetic manganese oxide (La07Sr03MnO3) was prepared by conventional electric ceramic technique. There are secondary phases, La07Sr03MnO3 and LaMnO3, existing at the grain boundaries. The content of insulating phase of LaMnO3 obviously affects the electrical properties of the samples. The samples still remained ferromagnetism after doping. Applied magnetic filed could change the electrical property. The resistance increased when magnetic field was applied, showing a positive magnetoresistance (PMR) phenomenon. The existence of PMR is due to the broadening of barrier at the grain boundaries caused by the magnetic field.
Optically transparent band-pass frequency selective surface
Feng Xiao-Guo, Gao Jin-Song, Li Xiao-Qiu
2008, 57 (5): 3193-3197. doi: 10.7498/aps.57.3193
Abstract +
Effects of the conductivity of transparent conductive film on the optically transparent band-pass frequency selective surface (FSS) are investigated by using Galerkin's method in the spectral domain. According to the results of the calculation and measurement, it is found that the conductivity of transparent conductive film mainly affects the transmission coefficient at the resonance frequency in radar wave band. The optically transparent band-pass frequency selective surface can transmit optical band and reflect radar wave band, however, it can also selectively transmit the radar wave.
Resonant transmission of the terahertz pulse through a subwavelength metallic slit
Meng Kuo, Chen Long-Wang, Zhang Yan, Wang Yan-Hua
2008, 57 (5): 3198-3202. doi: 10.7498/aps.57.3198
Abstract +
The transmission property of a single thin metallic slit with different widths has been investigated by terahertz (THz) time-domain spectroscopy. The experiment results show that in the effective spectroscopic range (02—26THz), the Fabry-Perot-like behavior was observed when the slit width decreases to a certain value. According to the theory of surface plasmon subwavelength optics, this resonant phenomenon was analyzed.
Transport of electrons through an asymmetric T-shaped quantum waveguide in a magnetic field
Tang Li-Ming, Wang Ling-Ling, Wang Ning, Yan Min
2008, 57 (5): 3203-3211. doi: 10.7498/aps.57.3203
Abstract +
We investigate transport properties of electrons through an asymmetric T-shaped magnetic quantum structure by the mode-mathcing technique and solution of the single electron Schrdinger equation. The results show that the changes of structural factors and magnetic field affect the electron scattering behavior and result in various patterns of electron transmission. When different magnetic configurations and structural factors are used, the transmission exhibits various patterns such as wide valley, sharp peak, resonant reflection, resonant transmission, and so on. Our results show that one may control the transmission property to design interferential quantum devices by adjusting magnetic configurations and or structural parameters.
Optimizing polymorphous silicon back surface field of a-Si(n)/c-Si(p) heterojunction solar cells by simulation
Zhao Lei, Zhou Chun-Lan, Li Hai-Ling, Diao Hong-Wei, Wang Wen-Jing
2008, 57 (5): 3212-3218. doi: 10.7498/aps.57.3212
Abstract +
Back surface field (BSF) effect of polymorphous silicon with different band gaps on a-Si(n)/c-Si(p) heterojunction solar cell was simulated and analyzed by utilizing AFORS-HET software. It was predicted that the polymorphous silicon capable of producing the optimal BSF effect is the microcrystalline silicon with band gap of 16 eV,the doped concentration of 1018cm-3 and the thickness about 5nm. Such microcrystalline silicon BSF is easy to realize in practice. It makes the efficiency of solar cell much higher than that using the conventional Al BSF with the same doping concentration.
Negative charging process of a grounded insulating thin film under low-energy electron beam irradiation
Li Wei-Qin, Zhang Hai-Bo
2008, 57 (5): 3219-3229. doi: 10.7498/aps.57.3219
Abstract +
The negative charging process and its mechanism caused by low-energy electron beam (e-beam) irradiation have been clarified for an insulating thin film with a grounded conductive substrate. Numerical simulation is performed by considering both electron scattering and electron transport, in combination with the Monte Carlo method and the finite difference method. The internal space charge, leakage current, surface potential and their time-evolution under e-beam irradiation are eventually obtained under different e-beam conditions and for different SiO2 film parameters. Results show that owing to the drift produced by mobility and diffusion, incident electrons can go beyond the conventional scattering region and arrive at the substrate after a certain transit time, forming negative space charge and leakage current. The transient negative charging process tends to equilibrium as the leakage current increases. In the equilibrium state, the leakage current increases with the energy and intensity of the e-beam. Meanwhile, the amount of net negative charge and the absolute value of surface potential increase with the film thickness, decrease with the increase of electron mobility, and both exhibit a maximum value with variation of the e-beam energy.
Study of the LC resonance giant magneto-impedance effect
Pan Hai-Lin, Cheng Jin-Ke, Zhao Zhen-Jie, He Jia-Kang, Ruan Jian-Zhong, Yang Xie-Long, Yuan Wang-Zhi
2008, 57 (5): 3230-3236. doi: 10.7498/aps.57.3230
Abstract +
CoP/Insulator/BeCu composite wire incorporating a capacitor was prepared by chemical deposition. This new type of composite wire functions as an LC resonance circuit element by itself, in which large LC resonance giant magneto-impedance (LCR-GMI) effect was observed when the driving frequency approached to the LC resonance frequency. The properties of LCR-GMI in the composite wire with a length of 95 cm were investigated. Its LCR-GMI ratio and field sensitivity are 4875% and 046%/A·m-1 at the resonance frequency of 29 MHz, respectively, which are higher than those of the ordinary composite wire. When the carrier frequency deviates from the resonance frequency, LCR-GMI ratio decreases obviously, showing distinct selectivity of frequency. Meanwhile, we proposed an equivalent circuit model based on the characteristics of the LC resonance composite wire, and simulated the experimental curves. The simulation results agreed well with the experimental data. Using the equivalent circuit model, we analyzed the physical mechanisms of LCR-GMI and the influence of wire length on the LCR-GMI effect.
Elastomechanical study of interface coupling in magnetoelectric bilayers
Cao Hong-Xia, Zhang Ning
2008, 57 (5): 3237-3243. doi: 10.7498/aps.57.3237
Abstract +
A theoretical model is introduced to derive the ME voltage coefficients of bilayer in free state according to the constitutive equations of magnetostrictive and piezoelectric phases. Using this model, the ME voltage coefficients of La07Sr03MnO3(LSMO)-PZT and Tb1-xDyxFe2-y (TDF)-PZT bilayers have been calculated and analyzed using the corresponding material parameters of individual phases. The results show that the ME voltage coefficient increases to a maximum at a given volume fraction of piezoelectric phase. With increasing interface coupling parameter k, an approximately linear increase of the maximum ME voltage coefficient have been observed. The maximum ME voltage coefficient for TDF-PZT bilayer reaches 19Vcm-1Oe-1, while for LSMO-PZT bilayer, the maximum value is only 165mVcm-1Oe-1. The theoretical results of ME voltage coefficients versus bias magnetic field for LSMO-PZT bilayer have been found to agree well with the measured data when k=02. Analysis shows that large magnetostriction, appropriate volume fraction and adequate interface coupling are key facters for obtaining excellent ME performance.
Analysis of the dynamics of upconversion in erbium-doped transparent lead lanthanum zirconate titanate ceramic
Li Xiao-Yan, Zheng Zhi-Qiang, Feng Zhuo-Hong, Liu Jing, Jiang Cui-Hua, Kong Ling-Kai, Ming Hai
2008, 57 (5): 3244-3248. doi: 10.7498/aps.57.3244
Abstract +
The absorption and upconversion fluorescence spectra of Er3+ ions in Er3+ doped transparent lead lanthanum zirconate titanate(PLZT)ceramic were measured at room temperature. The radiative transition probabilities of the Er3+ ions were calculated using the absorption spectrum of Er3+ doped PLZT. Strong upconversion emission was observed in the upconversion luminescence of Er3+ doped PLZT. The green emission intensities at 540nm and 564nm were stronger than the red emission intensity at 678nm. The upconversion rate equations describing the dynamic process of the system have been deduced. The upconversion coefficients were estimated by numerically solving the rate equations and fitting the simulated curves to the measured data. The coefficients C22and C33 obtained are 091×10-18cm3/s and 1823×10-18cm3/s, respectively. The results show that evident upconvesion phenomenon can be observed in Er3+: PLZT transparent ceramics, which is consistent with our observation.
Study of complete bandgap of two-dimensional columnar photonic crystals
Cheng Xu-Pan, Cao Quan-Xi
2008, 57 (5): 3249-3253. doi: 10.7498/aps.57.3249
Abstract +
Plane wave expansion method was employed to study the relation between the bandgap of two-dimensional columnar photonic crystals and the filling ratio and dielectric constant ratio. It is shown that the complete bandgap does not increase monatonically with the dielectric constant ratio, but has a peak value instead.
Investigation of the charge-transfer spectra of Ce4+-doped Ca2SnO4 with one-dimensional structure
Fu Shi-Liu, Chai Fei, Chen Jie, Zhang Han-Yan
2008, 57 (5): 3254-3259. doi: 10.7498/aps.57.3254
Abstract +
Ca2Sn1-xCexO4 and Ca2-ySrySn1-xCexO4 with one-dimensional structures were prepared by the solid-state reaction method. The X-ray photoelectron spectra of Ce4+-doped Ca2SnO4 showed the existence of two oxidation states of O2- ions with binding energy peaks at 5277 eV and 5293 eV. The former corresponds to the terminal O2- ions in the SnO6 octahedra while the latter corresponds to the equatorial O2- ions of the octahedra. The luminescence from Sr2CeO4 and Ca2Sn1-xCexO4 phosphors with one-dimensional structures originates from a ligand-to-metal Ce4+ charge transfer (CT) and it is generally accepted that there exist two excitation peaks in the ultraviolet excitation band. However, it was found from the Ca2-ySrySn1-xCexO4 sample that the excitation band of Ca2Sn1-xCexO4 was actually comprised of three excitation peaks which were centered at about 31000, 34500 and 37400cm-1. When Sr2+ ions were doped in Ca2Sn1-xCexO4, three excitation components peaking at about 31200, 34700 and 38400cm-1 were observed apparently, whose locations exhibited a blue shift as compared with those of Ca2Sn1-xCexO4. However, the substitution of Ca2+ by Sr2+ had no influence on the shape of the emission spectrum. The excitation spectrum of Sr2CeO4 can also be deconvoluted into three Gassian components which are centered at about 29300, 33400 and 37000cm-1, respectively.
Optical property of modulated n-doped ZnSe/BeTe type-Ⅱ quantum wells
Akimoto Ryoichi, Ji Zi-Wu, Kojima Eiji, Takeyama Shojiro, Mino Hirofumi
2008, 57 (5): 3260-3266. doi: 10.7498/aps.57.3260
Abstract +
We report the optical properties of the modulated n-doped ZnSe/BeTe/ZnSe type-Ⅱ quantum wells. The reflection spectra have shown typical negatively charged exciton features only in a doped sample. The luminescence spectra and the polarization anisotropy depend strikingly on both the n-doping into the barrier layers and an applied external electric field perpendicular to the layer. These are explained by screening of the built-in electric field with n-doping and Stark effects due to the applied electric field. The electron density as well as the mass was determined in high magnetic field (up to 160 T) cyclotron-resonance measurements. It was found that the observed indirect PL transition occurs via the charged excitons in a type-II quantum configuration.
Study of photoluminescence and energy transfer properties of an organic dye salt doped thin films
Xu Deng, Ye Li-Hua, Cui Yi-Ping, Xi Jun, Li Li, Wang Qiong
2008, 57 (5): 3267-3270. doi: 10.7498/aps.57.3267
Abstract +
The photoluminescence and energy transfer properties based on an organic salt trans-4-[p-(N-ethyl-N-(hydroxylethyl)amino)phenylstyryl]-N-(hydroxyethyl)pyridinium iodide (ASPI) doped PVK thin film were investigated by steady-state and time-resolved fluorescent spectra. We observed that the emission intensity and the fluorescent lifetime of PVK reduced with increasing ASPI doping concentration due to the Forster energy transfer from PVK to ASPI, which is strongly correlated with an efficient spectral overlap between ASPI absorption and PVK emission. We also added some Alq3 into the doping system as energy carriers in order to increase the energy transfer efficiency from PVK to ASPI at low concentration, or there will be an evident decrease in photoemission efficiency due to the concentration quenching at high concentration. The dynamical process of energy transfer is discussed.
Analysis of positron annihilation in carbon allotropes
Chen Xiang-Lei, Kong Wei, Weng Hui-Min, Ye Bang-Jiao
2008, 57 (5): 3271-3275. doi: 10.7498/aps.57.3271
Abstract +
Superposed-neutral-atom model and the finite-difference method (SNA-FD) are used to calculate the positron annihilation lifetime in graphite, diamond and C60 We find that in graphite with laminar structure,the main place where the positron exists and annihilation takes place is the space between graphite layers. Positron lifetime of graphite is calculated to be 208ps, which agrees with the published experimental result. In diamond, the main place where positron exists and annihilation takes places is the space between carbon atoms. Positron lifetime of diamond is calculated to be 1150ps, which agrees with the published experimental result. In C60 with a fcc structure, the main area where positron exits is the space near the spherical molecule shell of C60 and the space between molecules. The main area where positron annihilation takes place is the space between molecules. Positron lifetime of C60 is calculated to be 352ps, which falls in the range of positron lifetime of C60 published in literature.
Study of one-dimensional spatial distribution of the plasma luminous radicals during depositing silicon films
Chen Fei, Zhang Xiao-Dan, Zhao Ying, Wei Chang-Chun, Sun Jian
2008, 57 (5): 3276-3280. doi: 10.7498/aps.57.3276
Abstract +
One-dimensional spatial distribution of the plasma luminous radicals during depositing silicon films and its online monitoring were studied using optical emission spectroscopy. The results indicated that there existed an evident luminous zone in the middle of the plasma and a dark zone near the two electrodes. The intensity of SiH* and Hα* peak increased with the increase of silane concentration, power, and the incorporation of borane. Crystalline volume fraction of thin films decreased with the increase of borane flow rate, but the ratio of I[Hα*]/I[SiH*] was also increased. The ratio of I[Hα*]/I[SiH*] varied in different ways at different positions with the variation of silane concentration. However, an unigue variation of the ratio all over the plasma is observed with the variation of the discharge power or the borane flow rate.
Steered molecular dynamics investigation of force-induced detachment of adsorbed single polymer chains
Wang Yu, Zhang Lin-Xi
2008, 57 (5): 3281-3286. doi: 10.7498/aps.57.3281
Abstract +
The dynamics of the detachment of single polyethylene (PE) chain from a strongly adsorbing surface in vacuum is investigated by steered molecular dynamics method. When the chain is pulled from the monomer of N/3 (here N is the chain length), there are two force plateaus for the curve of the average force 〈f〉 probed by the ideal spring as a function of pulling distance Z,which agrees well with the experimental results. There are four different stages during the detachment of single polyethylene (PE) chains. As the chains are pulled in an inclined direction from one end, there exist always a linear relationship for average force probed by the ideal spring vs inclination angle θ for θ>20 degrees Furthermore, the slope of the line increases with the pulling velocity. However, for θ<20 degrees, the average force probed by the ideal spring tends to a fixed value of 780pN.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Air bubble entrainment by breaking waves and estimation of the related statistical quantities
Zhang Shu-Wen
2008, 57 (5): 3287-3292. doi: 10.7498/aps.57.3287
Abstract +
Based on the experiments, the energy loss from wave breaking εed, the bubble plume penetration depth zb, the rate of air entrainment Q(z), and the turbulent kinetic energy dissipation rate εT(z) are estimated in this study. As a consequence, a simple bubble size spectrum model N(a,z) is proposed and the rate of energy dissipation due to air bubble entrainment and bubble fragment Hinze scale and bubble size spectrum are investigated under different sea states. It is indicated that the rate of energy dissipation due to air bubble entrainment ranges from 01 to 06 in low and moderate sea states, but may be negligible in the high sea state. Bubble fragment Hinze scale downshifts to the lower-frequency band as wind speed increases. Bubble size spectrum not only depends on the rate of air entrainment, the breaking rate, and the turbulent kinetic energy dissipation rate, but also strongly on the wind and sea state.
Numerical simulation of ozone generation in oxygenic plasmas
Ouyang Jian-Ming, Shao Fu-Qiu, Lin Ming-Dong
2008, 57 (5): 3293-3297. doi: 10.7498/aps.57.3293
Abstract +
The generation processes of ozone in oxygen plasmas and atmospheric plasmas were numerically simulated in this paper. It is concluded that the generation of ozone is closely correlated with free oxygen atoms, and the maximum number density of ozone is correlated with the initial electron number density. The best discharge interval is the time when the number density of oxygen atoms is maximal.