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Volume 23 Issue 6
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Original Articles
On Finding Global Smooth Solutions to the Landau--Lifshitz Equation
CHEN Jian-Qing, GUO Bo-Ling
Chin. Phys. Lett. 2006, 23 (6): 1359-1360 .  
Abstract   PDF(pc) (178KB) ( 504 )
We prove that n-dimensional radial symmetric Landau--Lifshitz equation possesses at least two classes of global smooth solutions with suitable initial-boundary conditions.
Darboux Transformation of a Differential--Difference Equation and Its Explicit Solutions
LI Wen-Min, GENG Xian-Guo
Chin. Phys. Lett. 2006, 23 (6): 1361-1364 .  
Abstract   PDF(pc) (267KB) ( 621 )
The Darboux transformation of a differential--difference equation associated with a 3×3 matrix spectral problem is derived. As an application, explicit soliton solutions of the differential--difference equation are presented.
Exactly Solvable Combinations of Scalar and Vector Potentials for the Dirac Equation Interrelated by Riccati Equations
Axel Schulze-Halberg
Chin. Phys. Lett. 2006, 23 (6): 1365-1368 .  
Abstract   PDF(pc) (185KB) ( 577 )
New classes of solvable scalar and vector potentials for the Dirac equation are obtained, together with the associated exact Dirac spinors. The method of derivation is based on an a priori constraint between the solutions, leading to an interrelation between the scalar and vector potential in the form of a Riccati equation. The present note generalizes a series of former articles.
Discussion on Maximally Entangled States of Two Coupled Two-Level Particles by Coherent State Approximation
ZHANG Zheng-Jie, WANG Ke-Lin,
Chin. Phys. Lett. 2006, 23 (6): 1369-1371 .  
Abstract   PDF(pc) (281KB) ( 422 )
We analyse the best condition for generating the maximally entangled states of the system containing two coupled two-level particles by the coherent approximation method beyond rotating wave approximation. It is found that the maximally entangled states are obtained when the detuning ν and the strength Ω of driving laser satisfy the condition ν/Ω =2.5. The maximum average probability of entangled state pa max(ν, Ω) has the best stability relying on ν and Ω when ν approx 2Ω.
Scheme for Robust Long-Distance Continuous Variable Quantum Key Distribution
ZHANG Yong-Sheng, GUO Guang-Can
Chin. Phys. Lett. 2006, 23 (6): 1372-1374 .  
Abstract   PDF(pc) (173KB) ( 461 )
It is shown that the configuration of phase coding for quantum key distribution with single photon can also be used for continuous variable quantum key distribution. Therefore the robust long-distance high-speed quantum key distribution can be achieved with current technology.
High Efficient Quantum Key Distribution by Random Using Classified Signal Coherent States
LI Jing-Bo, FANG Xi-Ming
Chin. Phys. Lett. 2006, 23 (6): 1375-1378 .  
Abstract   PDF(pc) (235KB) ( 489 )
The decoy-state method is a useful method in resisting the attacks on quantum key distribution. However, how to choose the intensities of decoy states and the ratio of the decoy states and the signal state is still an open question. We present a simple formula to analyse the problem. We also give a simple method to derive the bounds of the necessary counting rates and quantum bit error rates for BB84 and SARG04; the latter was previously proposed by Scarani et al. [Phys. Rev. Lett. 92(2004)057901] We then propose a multi-signal-state method which employs different coherent states either as the decoy state or as the signal state to carry out quantum key distribution. We find our protocol more efficient and feasible.
Theoretical Study of Quantum Bit Rate in Free-Space Quantum Cryptography
MA Jing, ZHANG Guang-Yu, TAN Li-Ying
Chin. Phys. Lett. 2006, 23 (6): 1379-1382 .  
Abstract   PDF(pc) (213KB) ( 492 )
The quantum bit rate is an important operating parameter in free-space quantum key distribution. We introduce the measuring factor and the sifting factor, and present the expressions of the quantum bit rate based on the ideal single-photon sources and the single-photon sources with Poisson distribution. The quantum bit rate is studied in the numerical simulation for the laser links between a ground station and a satellite in a low earth orbit. The results show that it is feasible to implement quantum key distribution between a ground station and a satellite in a low earth orbit.
Secure Quantum Secret Sharing Based on Reusable GHZ States as Secure Carriers
SONG Jie, ZHANG Shou
Chin. Phys. Lett. 2006, 23 (6): 1383-1836 .  
Abstract   PDF(pc) (126KB) ( 503 )
We show that a potential eavesdropper can eavesdrop whole secret information when the legitimate users use secure carrier to encode and decode classical information repeatedly in the protocol proposed by Bagherinezhad S and Karimipour V [Phys. Rev. A 67(2003)044302]. Then we present a revised quantum secret sharing protocol by using the Greenberger--Horne--Zeilinger state as secure carrier. Our protocol can resist Eve’s attack.
Self-Trapping of Two Bose--Einstein Condensates with a Coupling Drive
QIU Jian-Guo
Chin. Phys. Lett. 2006, 23 (6): 1387-1390 .  
Abstract   PDF(pc) (205KB) ( 413 )
We present an approximate analytical solution to the population imbalance of two-component Bose--Einstein condensate with the coupling drive. The dependence of the time evolution of self-trapping upon the radio frequency wave, the Rabi coupling frequency, the initial atom number and relative phase between two condensates are investigated. The lower radio frequency wave, the same atom number and initial relative phase between condensates are beneficial to observe the self-trapping.
Ground State Properties for Bose-Condensed Gas in Anisotropic Traps
XU Zhi-Jun, LI Hai-Bin, XIN Xiao-Tian, LI Zhen, WANG Dong-Mei
Chin. Phys. Lett. 2006, 23 (6): 1391-1394 .  
Abstract   PDF(pc) (242KB) ( 472 )
Based on the energy functional and variational method, we present a new method to investigate the ground state properties for a weakly interacting Bose-condensed gas in an anisotropic harmonic trap at zero temperature. With this method we are able to find the analytic expression of the ground-state wavefunction and to explore the relevant quantities, such as energy, chemical potential, and the aspect ratio of the velocity distribution. These results agree well with previous ground state numerical solutions of the Gross--Pitaevskii equation given by Dalfovo et al. [Phys. Rev. A 53 (1996) 2477] This new method is simple compared to other methods used to solve numerically the Gross--Pitaevskii equation, and one can obtain analytic and reliable results.

Energy--Momentum Pseudo-Tensor of Relic Gravitational Wave of Both the Polarized States
ZHANG Xian-Hong, LI Fang-Yu
Chin. Phys. Lett. 2006, 23 (6): 1395-1397 .  
Abstract   PDF(pc) (181KB) ( 519 )
Unlike usual celestial gravitational waves, the relic gravitational waves (RGWs) form random signals in curved spacetime background. We calculate the energy--momentum pseudo-tensor of a certain component of the RGWs propagating along arbitrary directions in Cartesian coordinates. It is found that the energy density of RGWs is positive definitely, and the momentum density components have reasonable behaviour. Such results may provide a theoretical basis for the detection of RGWs.
Effects of Nonlinear Time-Delay on a Stochastic Asymmetric System
WANG Jiu-Yun, ZHU Chun-Lian, JIA Ya, LI Jia-Rong
Chin. Phys. Lett. 2006, 23 (6): 1398-1401 .  
Abstract   PDF(pc) (225KB) ( 420 )
We numerically investigate the effects of nonlinear time-delay on the stochastic system. With the delay time increasing, it is found that the peak of probability distribution in low steady states is decreased, and the peak of probability distribution in high steady states is increased. The mean of state variable, the normalized variance, and the normalized autocorrelation function which quantifies the concentrated degree are slowly varied for small delay time. However, the mean of state variable is rapidly increased, and the normalized variance and the normalized autocorrelation function is rapidly decreased for large delay time.

Improvement of the Hopfield Neural Network by MC-Adaptation Rule
ZHOU Zhen, ZHAO Hong
Chin. Phys. Lett. 2006, 23 (6): 1402-1405 .  
Abstract   PDF(pc) (212KB) ( 494 )
We show that the performance of the Hopfield neural networks, especially the quality of the recall and the capacity of the effective storing, can be greatly improved by making use of a recently presented neural network designing method without altering the whole structure of the network. In the improved neural network, a memory pattern is recalled exactly from initial states having a given degree of similarity with the memory pattern, and thus one can avoids to apply the overlap criterion as carried out in the Hopfield neural networks.
Chaos Synchronization Criterion and Its Optimizations for a Nonlinear Transducer System via Linear State Error Feedback Control
SHEN Jian-He, CHEN Shu-Hui, CAI Jian-Ping
Chin. Phys. Lett. 2006, 23 (6): 1406-1409 .  
Abstract   PDF(pc) (238KB) ( 712 )
Global chaos synchronization of two identical nonlinear transducer systems is investigated via linear state error feedback control. The sufficient criterion for global chaos synchronization is derived firstly by the Gerschgorin disc theorem and the stability theory of linear time-varied systems. Then this sufficient criterion is further optimized in the sense of reducing the lower bounds of the coupling coefficients with two methods, one based on Gerschgorin disc theorem itself and the other based on Lyapunov direct method. Finally, two optimized criteria are compared theoretically.
Synchronization of Coupled Oscillators on Newman--Watts Small-World Networks
GUAN Jian-Yue, XU Xin-Jian, WU Zhi-Xi, WANG Ying-Hai
Chin. Phys. Lett. 2006, 23 (6): 1410-1413 .  
Abstract   PDF(pc) (254KB) ( 513 )
We investigate the collection behaviour of coupled phase oscillators on Newman--Watts small-world networks in one and two dimensions. Each component of the network is assumed as an oscillator and each interacts with the others following the Kuramoto model. We then study the onset of global synchronization of phases and frequencies based on dynamic simulations and finite-size scaling. Both the phase and frequency synchronization are observed to emerge in the presence of a tiny fraction of shortcuts and enhanced with the increases of nearest neighbours and lattice dimensions.
Hexagonal Standing-Wave Patterns in Periodically Forced Reaction--Diffusion Systems
ZHANG Ke, WANG Hong-Li, QIAO Chun, OUYANG Qi
Chin. Phys. Lett. 2006, 23 (6): 1414-1417 .  
Abstract   PDF(pc) (298KB) ( 632 )
The periodically forced spatially extended Brusselator is investigated in the oscillating regime. The temporal response and pattern formation within the 2:1 frequency-locking band where the system oscillates at one half of the forcing frequency are examined. An hexagonal standing-wave pattern and other resonant patterns are observed. The detailed phase diagram of resonance structure in the forcing frequency and forcing amplitude parameter space is calculated. The transitions between the resonant standing-wave patterns are of hysteresis when control parameters are varied, and the presence of multiplicity is demonstrated. Analysis in the framework of amplitude equation reveals that the spatial patterns of the standing waves come out as a result of Turing bifurcation in the amplitude equation.
Projective Synchronization in Time-Delayed Chaotic Systems
FENG Cun-Fang, ZHANG Yan, WANG Ying-Hai
Chin. Phys. Lett. 2006, 23 (6): 1418-1421 .  
Abstract   PDF(pc) (198KB) ( 602 )
For the first time, we report on projective synchronization between two time delay chaotic systems with single time delays. It overcomes some limitations of the previous work, where projective synchronization has been investigated only in finite-dimensional chaotic systems, so we can achieve projective synchronization in infinite-dimensional chaotic systems. We give a general method with which we can achieve projective synchronization in time-delayed chaotic systems. The method is illustrated using the famous delay differential equations related to optical bistability. Numerical simulations fully support the analytical approach.
Anomalously Strong Scattering of Spontaneously Produced Laser Radiation in the First Free-Electron Laser and Study of Free-Electron Two-Quantum Stark Lasing in an Electric Wiggler with Quantum-Wiggler Electrodynamics
S. H. Kim
Chin. Phys. Lett. 2006, 23 (6): 1422-1425 .  
Abstract   PDF(pc) (161KB) ( 344 )
We calculate the scattering cross section of an electron with respect to the spontaneously produced laser radiation in the first free-electron laser (FEL) with quantum-wiggler electrodynamics (QWD). The cross section is 1016 times the Thomson cross section, confirming the result obtained by a previous analysis of the experimental data. A QWD calculation show that spontaneous emission in an FEL using only an electric wiggler can be very strong while amplification through net stimulated emission is practically negligible.
On the Physical Contents of the Light-Cone QCD Effective Hamiltonian on Meson Sector
WANG Shun-Jin, LI Lei, ZHOU Shan-Gui, ZHANG Guang-Biao
Chin. Phys. Lett. 2006, 23 (6): 1426-1429 .  
Abstract   PDF(pc) (240KB) ( 402 )
To explore the physical contents of the light-cone QCD effective Hamiltonian on meson sector, the mass spectra of flavour off-diagonal mesons consisting of (u,d,s,c,b) quarks and mesons consisting of heavy quarks cc- and bb- are calculated relativistically and nonperturbatively. Numerical results show that the present light-cone QCD effective Hamiltonian without confining potentials and flavour mixing interactions can well describe the ground states but can not apply for the excited states of the mesons. This result may imply that (i) the confining potential is indispensable for the excited states of mesons, (ii) the valence quark qq1 subspace is only valid for ground states but not for excited states. The above information may be significant for improving the light-cone QCD effective Hamiltonian approach, especially showing the urgent need to implement a confining potential and to enlarge the subspace of the meson sector for a more appropriate description of the excited states of the mesons.
Effect of 0h11/2 Level on Shell Model Calculations o 105Sb and 107Sb
Erdal Dikmen
Chin. Phys. Lett. 2006, 23 (6): 1430-1433 .  
Abstract   PDF(pc) (181KB) ( 439 )
The full and reduced shell model calculations have been carried out for the light odd--even 105Sb and 107Sb isotopes. The model space has been chosen as 1d5/2, 0g7/2, 1d3/2, 2s1/2, and 0h11/2 for the full calculations and excluded 0h11/2 for the reduced calculations. The reduced shell model calculations of 105Sb and 107Sb isotopes are presented for the first time. We obtain the energy spectra for the 105Sb and 107Sb isotopes in the full and reduced model space by using CD-Bonn two-body effective nucleon--nucleon interaction. The resulting energy spectra are compared to the experimental results to understand the effect of the 0h11/2 level on the shell model calculations. We draw conclusions about the right model space in the shell model calculations for the isotopes around the N=Z=50 region of the periodic table.
Evaluation of Transmutation of 137Cs(g,n) 136Cs Using Ultra-Intense Lasers in Solid Targets
R. Sadighi-Bonabi, O. Kokabee,
Chin. Phys. Lett. 2006, 23 (6): 1434-1436 .  
Abstract   PDF(pc) (211KB) ( 451 )
Relativistic electrons produced in ultra-intense laser--solid interaction generate highly collimated g-ray beams through Bremsstrahlung that can be used to induce photonuclear reactions. Photonuclear transmutation (of (g,n) type) of 137Cs, one of the hazardous nuclear wastes with half-life of 30.17 years which cannot be transmuted practically with neutron bombardment due to its very low neutron capture cross section, has been considered. Nuclear activity of produced 136Cs with half-life of 13.16 days has been evaluated analytically using available experimental data. With irradiating a 137Cs sample by p-polarized laser light of 1020Wcm-2 and the repetition rate of 10Hz for 30min, the activity of 0.24 Bq is obtained. It is found that intensity has a large effect in yield around 1021Wcm-2. For similar laser with intensity of 5×1021Wcm-2, the activity increases with a factor of 105.

Isotope Dependence of Superheavy Nucleus Formation Cross Section
LIU Zu-Hua, BAO Jing-Dong,
Chin. Phys. Lett. 2006, 23 (6): 1437-1440 .  
Abstract   PDF(pc) (222KB) ( 378 )
The dynamical process in the superheavy nucleus synthesis is studied on the basis of the two-dimensional Smoluchowski equation. Special attention is paid to the isotope dependence of the cross section for the superheavy nucleus formation by means of making a comparison among the reaction systems of 54Fe + 204Pb, 56Fe + 206Pb, and 58Fe + 208Pb. It is found by this comparison that the formation cross section is very sensitive to the conditional saddle-point height and the neutron separation energy of the compound nucleus. Reaction systems with lower height of conditional saddle-point and smaller neutron separation energy are more favourable for the synthesis of the superheavy nucleus.
Pronounced Fluctuations of Target Fragments in Forward Hemisphere Only in Ultra Relativistic Nuclear Collision
Dipak Ghosh, Argha Dev, Samabrata Sarkar, Prabir Kumar Haldar
Chin. Phys. Lett. 2006, 23 (6): 1441-1444 .  
Abstract   PDF(pc) (213KB) ( 917 )
Dynamical fluctuation of target evaporated black particles is investigated in both forward and backward hemispheres within the framework of multi-dimensional factorial moment methodology using the brilliant concept of the Hurst exponent. We analyse the black particles emitted in 32S--AgBr interactions at 200AGeV and it is evident that the dynamical fluctuation in the backward hemisphere is self-affine. In the forward hemisphere, dynamical fluctuation is self-similar but not self-affine. However, study indicates that the fluctuation in the forward hemisphere is more pronounced than that in backward hemisphere.
Absence of Charge-Resonance-Enhanced Ionization in Attosecond Pulse Photoionization: Numerical Result on One-Dimensional H2+
ZHANG Zhe, ZHANG Gui-Zhong, XIANG Wang-Hua, W. T. Hill III
Chin. Phys. Lett. 2006, 23 (6): 1445-1447 .  
Abstract   PDF(pc) (145KB) ( 477 )
We present a numerical result of photoionization rate for the one-dimensional molecular hydrogen ion model exposed to intense light of 1×1016-2×1016W/cm2, 55-as pulse duration, and 800nm wavelength. In contrast to the previous calculation result of charge-resonance-enhanced ionization for lower intensity and much longer pulse, our result exhibits an ionization saturation. The numerical results are interpreted in the field-dressed potential picture as over-the-barrier liberation of electrons. This extremely short pulsewidth and relatively high field phenomenon requests experimental demonstration.
Formation of Charged Particle Tracks in Solids
Mukhtar A. Rana
Chin. Phys. Lett. 2006, 23 (6): 1448-1451 .  
Abstract   PDF(pc) (198KB) ( 938 )
A criterion for formation of etchable tracks in solids is suggested using the well-known concepts of ionization and thermal spikes, diffusion process with useful and justified assumptions, and present or published experimental and theoretical investigations on the same subject. The suggested criterion is useful for a wide spectrum of researchers including development and applications of track recording materials, ions implantation, sputtering and other areas, which include interactions of charged particles with solids.
Average Energy Loss Measured in Single and Double Electron Capture Collisions of He2+ on Ar at Low Velocities
LI Bin, MA Xin-Wen, ZHU Xiao-Long, LIU Hui-Ping, ZHANG Shao-Feng, QIAN Dong-Bin, CHEN Lan-Fang, FENG Wen-Tian, CAO Shi-Ping, SHA Shan, ZHANG Da-Cheng,
Chin. Phys. Lett. 2006, 23 (6): 1452-1455 .  
Abstract   PDF(pc) (254KB) ( 453 )
Employing the recoil ion momentum spectroscopy we investigate the collision between He2+ and argon atoms. By measuring the recoil longitudinal momentum the energy losses of projectile are deduced for capture reaction channels. It is found that in most cases for single- and double-electron capture, the inner electron in the target atom is removed, the recoil ion is in singly or multiply excited states (hollow ion is formed), which indicates that electron correlation plays an important role in the process. The captured electrons prefer the ground states of the projectile. It is experimentally demonstrated that the average energy losses are directly related to charge transfer and electronic configuration
Multiband Terahertz Photonic Band Gaps of Subwavelength Planar Fractals
ZHAO Guo-Zhong, TIAN Yan, SUN Hong-Qi, ZHANG Cun-Lin, YANG Guo-Zhen
Chin. Phys. Lett. 2006, 23 (6): 1456-1458 .  
Abstract   PDF(pc) (221KB) ( 502 )
Optical transmission properties of subwavelength planar fractals in terahertz (THz) frequency regime are studied by means of time-domain spectroscopy. The transmission spectra with multiple pass bands and stop bands are observed. The tunable photonic band gaps are realized by changing the angle between the principle axis of planar fractal and the polarization of THz wave. The possible application of the subwavelength optical component is discussed. We attribute the detected transmittance from subwavelength fractals to localized resonances.
Cascade Grating Structure for Increasing the Channel Number on Holographic Demultiplexer
Jun Won AN
Chin. Phys. Lett. 2006, 23 (6): 1459-1461 .  
Abstract   PDF(pc) (194KB) ( 475 )
The expansion capability of the channel number in the optical demultiplexer using two cascaded photopolymer volume gratings is reported. It could be accomplished by designing of two gratings with different spectral range. As a result of the experiment, a 0.4-nm-spaced 130-channel demultiplexer with the channel uniformity of 3.5dB, the 3dB-bandwidth of 0.12nm, and the channel crosstalk of -20dB is experimentally demonstrated.
Anomalous Behaviour of Photorefractive Grating Erasure Owing to Existence of both Negative and Positive Carriers
ZHU Rong, LIU De-An, GUO Yuan-Jun, CHAI Zhi-Fang, LIU Li-Ren
Chin. Phys. Lett. 2006, 23 (6): 1462-1465 .  
Abstract   PDF(pc) (225KB) ( 391 )
In LiNbO3:Fe, anomalous behaviour of grating erasure is observed with different wavelengths, i.e. rapid grating erasure in the short wavelength range, which deviates from the results predicted by the electron transport band model. The deviation is related to the coexistence of electrons and holes in photorefraction, and charge-transfer process including electrons and hole has been proposed. The electron and hole contributions to photoconductivity have been identified by experiments. We also give the theoretical dependence of electron photo-excitation coefficient S of the Fe centre on the wavelength.
Generation of Two-Atom Cluster State via Cavity QED
XIANG Shao-Hua, SONG Ke-Hui
Chin. Phys. Lett. 2006, 23 (6): 1466-1469 .  
Abstract   PDF(pc) (212KB) ( 593 )
We propose a physical scheme for generating a two-atom cluster state through the simultaneous interaction of two two-level atoms with a single-mode cavity field prepared initially in an odd-coherent state under a large-detuned limit. The influence of the dissipation constant, the intensity of the field and the imperfect manipulation on the preparation scheme are investigated. It is shown that when the intensity of the cavity is large enough, the influence of the cavity decay is efficiently suppressed. The possible error in the implementation of the cluster state is negligible when the time difference between two atoms crossing the cavity axis is small. It is suggested that the scheme can be realized by current technologies.
WG-Like Modes Selectivity in a Square Cavity with Posts
CHEN Qin, HUANG Yong-Zhen
Chin. Phys. Lett. 2006, 23 (6): 1470-1472 .  
Abstract   PDF(pc) (213KB) ( 442 )
We investigate the characteristics of Whispering-Gallery(WG)-like modes in a square cavity with posts by employing the two-dimensional (2D) finite-difference time-domain (FDTD) technique combined with the effective index method. The results indicate that the posts can result in mode selection in the WG-like modes. The WG-like modes with odd mode numbers are not much sensitive to the sizes of the posts. However, the quality factor (i.e. Q-factor) of the WG-like modes with even mode numbers decreases sharply with the increasing size of the posts. The decreasing Q-factor is attributed to mode leakage and scattering loss due to the presence of the post. The mode selection increases the mode spacing of square cavity twice in an optimized structure.
Multiwavelength Dispersion-Tuned Actively Mode-Locked Erbium-Doped Fibre Ring Laser with Gain Competition Suppression
PAN Shi-Long, LOU Cai-Yun
Chin. Phys. Lett. 2006, 23 (6): 1473-1475 .  
Abstract   PDF(pc) (186KB) ( 535 )
Multiwavelength dispersion-tuned actively mode-locked erbium-doped fibre ring laser is demonstrated by incorporating a section of highly nonlinear fibre (HNLF) in the laser cavity. The HNLF and the time gate element (modulator) in the fibre laser successfully suppress the gain competition in the erbium-doped fibre, and thus enable multiwavelength operation. Simultaneous generation of 10GHz pulses up to eight different wavelengths is achieved. Wavelength, spacing and modes number tuning are investigated by changing fibre cavity length, dispersion, and erbium-doped fibre amplifier power, respectively.
High Power Photonic Crystal Fibre Raman Laser
YAN Pei-Guang, RUAN Shuang-Chen, YU Yong-Qin, GUO Chun-Yu, GUO Yuan, LIU Cheng-Xiang
Chin. Phys. Lett. 2006, 23 (6): 1476-1478 .  
Abstract   PDF(pc) (195KB) ( 597 )
A cw Raman laser based on a 100-m photonic crystal fibre is demonstrated with up to 3.8W output power at the incident pump power of 12W, corresponding to an optical-to-optical efficiency of about 31.6%. The second order Stokes light, which is firstly reported in a cw photonic crystal fibre Raman laser, is obtained at 1183nm with an output power of 1.6W and a slope efficiency of about 45.7%.
Generation of 2.1W Continuous Wave Blue Light by Intracavity Doubling of a Diode-End-Pumped Nd:YAG Laser in a 30mm LBO
CHEN Ya-Hui, HOU Wei, PENG Hai-Bo, GENG Ai-Cong, ZHOU Yong, CUI Da-Fu, XU Zu-Yan
Chin. Phys. Lett. 2006, 23 (6): 1479-1481 .  
Abstract   PDF(pc) (218KB) ( 614 )
A folded four-mirror cavity with a composite Nd:YAG rod is optimized to obtain high efficient cw 473nm blue output. The laser could operate stably in the region of the thermal-lens focal length from 20mm to 70mm. LBO is used for intracavity frequency doubling of the 946nm transition of Nd:YAG and the optimum LBO length is investigated. A maximum output power of 2.1W in the blue spectral range at 473nm is achieved with 30-mm-long LBO, corresponding to an optical conversion efficiency of 9.1%.
Lengthening the Lifetime of Long Plasma Channel in Air Generated by Femtosecond Laser Pulse
CHEN Xiao, JIANG Hong-Bing, GONG Qi-Huang
Chin. Phys. Lett. 2006, 23 (6): 1482-1485 .  
Abstract   PDF(pc) (224KB) ( 367 )
We theoretically investigate the lifetime of self-guided plasma channel in air by launching an auxiliary delayed long-pulsed laser beam following an ultrashort laser. A detailed model makes the electron--ion recombination, the attachment of electrons on neutral particles, and particularly the impact ionization and electron-detachment mechanism incorporate. The calculated results show that the temporal evolution of electron density is greatly flattened and broadened. When the auxiliary laser intensity exceeds the threshold 3.32×104Wcm-2, the channel lifetime is distinctly prolonged from nanosecond to microsecond, or even longer due to the electrical field enhancement. Furthermore, with the laser intensity up to 109Wcm-2, the impact ionization overwhelms the detachment in effect. Thus, it is an effective way to extend the channel lifetime and provides a real opportunity for applications.
Poled Silica/DR1 Films with Thermally Stability and Large Electro-Optic Coefficient Applying in External Probe Tip
LIU Hong-Fei, HOU A-Lin, LIU Yun-Tao, ZHANG Da-Ming, CHUAI Xiao-Hong, YI Mao-Bin, SUN Wei
Chin. Phys. Lett. 2006, 23 (6): 1486-1489 .  
Abstract   PDF(pc) (209KB) ( 425 )
Sol-gel-processed silica films doped with Disperse Red 1(DR1) were prepared at 80°C aging temperature and 120°C baking temperature with corona poling to obtain stable and large electro-optic (EO) coefficient and film strength. A large EO coefficient of γ33=56pm/V was measured for the film of 0.5-μm thickness at the wavelength of 1300nm, and the value was unvaried at room temperature. Moreover, an external EO probe tip using the film was fabricated for the first time, and a signal voltage level corresponding to the EO signal was calibrated successfully.
Enhancement of Bichromatic High-Order Harmonic Generation by a Strong Laser Field and Its Third Harmonic
PI Liang-Wen, SHI Ting-Yun, QIAO Hao-Xue
Chin. Phys. Lett. 2006, 23 (6): 1490-1493 .  
Abstract   PDF(pc) (214KB) ( 536 )
We investigate high-order harmonic generation (HHG) in a linearly polarized bichromatic field composed of a fundamental laser field with frequency ω and an additional laser field with frequency 3ω. The numerical results show that it is possible to enhance the intensity of most high harmonics in orders of magnitude. A most striking feature in the enhancement is that the intensity of several special high harmonics is practically impaired as compared with that in the monochromatic case. The qualitative explanation to the great enhancement is that the additional high-frequency field can provide new transition paths for electrons to reach the continuum. The relative phase between the fundamental field and its third harmonic field also affects the intensity of high-order harmonics near the cutoff efficiently.
A 4.8-W M2=4.6 Continuous-Wave Intracavity Sum-Frequency Diode-Pumped Solid-State Yellow Laser
BO Yong, GENG Ai-Cong, LU Yuan-Fu, YANG Xiao-Dong, PENG Qin-Jun, CUI Qian-Jin, CUI Da-Fu, XU Zu-Yan
Chin. Phys. Lett. 2006, 23 (6): 1494-1497 .  
Abstract   PDF(pc) (230KB) ( 538 )
A yellow continuous wave with beam quality M2 = 4.6 and output power of 4.8W at 589nm is generated by intracavity sum-frequency mixing of 1064nm and 1319nm radiations of a Nd:YAG laser. To achieve high beam quality at high power, thermally near-unstable flat--flat resonators with two-rod birefringence compensation are designed to obtain the large fundamental mode size inside the Nd:YAG rods and the same beam width inside the KTP crystal. The optimal intracavity power ratio of both 1064nm and 1319nm beams is also considered. The output power fluctuation of the yellow laser remains less than 5% in four hours.
Correlation between Post-LASIK Starburst Symptom and Ocular Wavefront Aberrations
LIU Yong-Ji, MU Guo-Guang, WANG Zhao-Qi, WANG-Yan
Chin. Phys. Lett. 2006, 23 (6): 1498-1500 .  
Abstract   PDF(pc) (217KB) ( 380 )
Monochromatic aberrations in post laser in-situ keratomileusis (LASIK) eyes are measured. The data are categorized into reference group and starburst group according to the visual symptoms. Statistic analysis has been made to find the correlation between the ocular wavefront aberrations and the starburst symptom. The rms aberrations of the 3rd and 4th orders for the starburst group are significantly larger than those for the reference group. The starburst symptom shows a strong correlation with vertical coma, total coma, spherical aberrations. For 3-mm pupil size and 5.8-mm pupil size, the modulation transfer function (MTF) of the starburst group are lower than those of the reference group, but their visual acuities are close. MTF and PSF analyses are made for two groups, and the results are consistent with the statistical analysis, which means the difference between the two groups is mainly due to the third- and fourth-order Zernike aberrations.
Optical Planar Waveguides in KTiOPO4 Crystals by MeV Oxygen Ion Implantation
CHEN Feng, WANG Xue-Lin, WANG Ke-Ming, WANG Lei, JIAO Yang, WANG Liang-Ling, LU Qing-Ming, MA Hong-Ji, NIE Rui
Chin. Phys. Lett. 2006, 23 (6): 1501-1503 .  
Abstract   PDF(pc) (217KB) ( 516 )
We report on the optical planar waveguide formation in KTiOPO4 crystals by single or double oxygen ion implantation at energies of 2.4--3.0MeV and doses of 1015ions/cm2. The dark-line spectroscopy properties are investigated by a prism-coupling method. With an effective refractive index method, the refractive index profiles of the waveguides are reconstructed. The program code TRIM’98 (transport of ions in matter) is used to simulate the implantation process of oxygen ions into the KTiOPO4 crystal. It is found that an inherent relationship exists between the nuclear damage and the refractive index changes induced by the ion-beam implantation.
Pit Depth and Width Modulation Multilevel Run-Length Limited Read-Only Optical Storage
SONG Jie, PEI Jing, XU Duan-Yi, XIONG Jian-Ping, CHEN Ken, PAN Long-Fa
Chin. Phys. Lett. 2006, 23 (6): 1504-1506 .  
Abstract   PDF(pc) (207KB) ( 575 )
When the techniques of integrating the variation of the pit depth and width simultaneously are adopted to conventional DVD, the high-density multilevel run-length limited read-only optical storage method is achieved. The dynamic range of readout signal is greatly enlarged in comparison with keeping one parameter varied, and the recording levels number can be obviously increased. The discs can be manufactured using standard photoresist mastering and replication techniques with great compatibility to conventional binary read-only discs. Experimental results show that eight-level read-only optical disc can be realized and the capacity can be increased to 20GB.
Determination of Zero-Dispersion Wavelength by Four-Wave Mixing
JIN Xiao-Feng, ZHANG Xian-Min
Chin. Phys. Lett. 2006, 23 (6): 1507-1510 .  
Abstract   PDF(pc) (228KB) ( 660 )
We present an improved approach to determine the zero-dispersion wavelength by measurement of the four-wave mixing (FWM) effect employing the two-tunable-laser scanning method. The FWM behaviour of combined fibres with two different zero-dispersion wavelengths is investigated theoretically and experimentally. The results are compared with those by regular zero-dispersion wavelength test instrument using phase shift technique. The theoretical and experimental results confirm the feasibility of determination of zero-dispersion wavelength by FWM.
Heat Conduction and Characteristic Size of Fractal Porous Media
WANG Wei-Wei, HUAI Xiu-Lan, TAO Yu-Jia
Chin. Phys. Lett. 2006, 23 (6): 1511-1514 .  
Abstract   PDF(pc) (188KB) ( 728 )
Based on fractal theory, two types of random Sierpinski carpets (RSCs) and their periodic structures are generated to model the structures of natural porous media, and the heat conduction in these structures is simulated by the finite volume method. The calculated results indicate that in a certain range of length scales, the size and spatial arrangement of pores have significant influence on the effective thermal conductivity, and the heat conduction presents the aeolotropic characteristic. Above the length scale, however, the influence of size and spatial arrangement of pores on the effective thermal conductivity reduces gradually with the increasing characteristic size of porous media, the aeolotropic characteristic is weakened gradually. It is concluded that the periodicity in structures of porous media is not equal to the periodicity in heat conduction.

Axisymmetry Breaking to Travelling Waves in the Cylinder with Partially Heated Sidewall
MA Dong-Jun, SUN De-Jun, YIN Xie-Yuan
Chin. Phys. Lett. 2006, 23 (6): 1515-1518 .  
Abstract   PDF(pc) (258KB) ( 389 )
The transition from an axisymmetric stationary flow to three-dimensional time-dependent flows is carefully studied in a vertical cylinder partially heated from the side, with the aspect ratio A=2 and Prandtl number P4=0.021. The flow develops from the steady toroidal pattern beyond the first instability threshold, breaks the axisymmetric state at a Rayleigh number near 2000, and transits to standing or travelling azimuthal waves. A new result is observed that a slightly unstable flow pattern of standing waves exists and will transit to stable travelling waves after a long time evolution. The onset of oscillations is associated with a supercritical Hopf bifurcation in a system with O(2) symmetry.
Direct Numerical Simulation of a Spatially Evolving Supersonic Turbulent Boundary Layer at Ma=6
LI Xin-Liang, FU De-Xun, MA Yan-Wen
Chin. Phys. Lett. 2006, 23 (6): 1519-1522 .  
Abstract   PDF(pc) (302KB) ( 475 )
Direct numerical simulation is carried out for a spatially evolving supersonic turbulent boundary layer at free-stream Mach number 6. To overcome numerical instability, the seventh-order WENO scheme is used for the convection terms of Navier--Stokes equations, and fine mesh is adopted to minimize numerical dissipation. Compressibility effects on the near-wall turbulent kinetic energy budget are studied. The cross-stream extended self-similarity and scaling exponents including the near-wall region are studied. In high Mach number flows, the coherence vortex structures are arranged to be smoother and streamwised, and the hair-pin vortices are less likely to occur.
Controlling Flow Turbulence Using Local Pinning Feedback
TANG Guo-Ning, HU Gang,
Chin. Phys. Lett. 2006, 23 (6): 1523-1526 .  
Abstract   PDF(pc) (304KB) ( 366 )
Flow turbulence control in two-dimensional Navier--Stokes equation is considered. By applying local pinning control only to a single component of flow velocity field, the flow turbulence can be controlled to desirable targets. It is found that with certain number of controllers there exist an optimal control strength at which control error takes minimum value, and larger and smaller control strengths give worse control efficiency. The physical mechanism underlying these strange control results is analysed based on the interactions between different types of modes.
Relativistic Electron Acceleration in a Wake Field Generated by the Intense Femtosecond Laser Interaction with a Mixture Jet of Deuterium Clusters and Molecules
LIU Hong-Jie, GU Yu-Qiu, ZHENG Zhi-Jian, JIAO Chun-Ye, NAM Sung-Mo, HAN Zai-Min, WANG Xiang-Xian, HE Ying-Ling, WEN Tian-Shu, ZHANG Shuang-Gen, WEN Xian-Lun, ZHOU Kai-Nan, WANG Xiao-Dong, HUANG Xiao-Jun, HUA Jian-Fei
Chin. Phys. Lett. 2006, 23 (6): 1527-1529 .  
Abstract   PDF(pc) (248KB) ( 574 )
High energy electron acceleration in a wake field generated in the intense ultrashort (30fs) laser pulse cluster gas jet interaction is experimentally demonstrated. Relativistic electrons with energy of 60MeV were observed. These high energy electrons split into two beams due to the relativistic self-focusing of the laser.
Numerical Simulation on Expansion Process of Ablation Plasma Induced by Intense Pulsed Ion Beam
TAN Chang, LIU Yue, WANG Xiao-Gang, MA Teng-Cai
Chin. Phys. Lett. 2006, 23 (6): 1530-1532 .  
Abstract   PDF(pc) (227KB) ( 412 )
We present a one-dimensional time-dependent numerical model for the expansion process of ablation plasma induced by intense pulsed ion beam (IPIB). The evolutions of density, velocity, temperature, and pressure of the ablation plasma of the aluminium target are obtained. The numerical results are well in agreement with the relative experimental data. It is shown that the expansion process of ablation plasma induced by IPIB includes strongly nonlinear effects and that shock waves appear during the propagation of the ablation plasma.
Deposition of TiN Films by Novel Filter Cathodic Arc Technique
NIU Er-Wu, FAN Song-Hua, LI Li, LU Guo-Hua, FENG Wen-Ran, ZHANG Gu-Ling, YANG Si-Ze
Chin. Phys. Lett. 2006, 23 (6): 1533-1535 .  
Abstract   PDF(pc) (211KB) ( 580 )
A straight magnetic filtering arc source is used to deposit thin films of titanium nitride. The properties of the films depend strongly on the deposition process. TiN films can be deposited directly onto heated substrates in a nitrogen atmosphere or onto unbiased substrates by condensing the Ti+ ion beam in about 300eV N2+ nitrogen ion bombardment. In the latter case, the film stoichiometry is varied from an N:Ti ratio of 0.6--1.1 by controlling the arrival rates of Ti and nitrogen ions. Meanwhile, simple models are used to describe the evolution of compressive stress as function of the arrival ratio and the composition of the ion-assisted TiN films.
Hydrogen Storage in Benzene Moiety Decorated Single-Walled Carbon Nanotubes
ZHANG Bing-Yun, LIANG Qi-Min, SONG Chen, XIA Yue-Yuan, ZHAO Ming-Wen, LIU Xiang-Dong, ZHANG Hong-Yu
Chin. Phys. Lett. 2006, 23 (6): 1536-1549 .  
Abstract   PDF(pc) (303KB) ( 458 )
The hydrogen storage capacity of (5, 5) single-walled carbon nanotubes (SWNTs) decorated chemically with benzene moieties is studied by using molecular dynamics simulations (MDSs) and density functional theory (DFT) calculations. It is found that benzene molecules colliding on (5, 5) SWNTs at incident energy of 50eV form very stable configurations of benzene moiety adsorption on the wall of SWNTs. The MDSs indicate that when the benzene moiety decorated (5, 5) SWNTs and a pristine (5, 5) SWNT are put in a box in which hydrogen molecules are filled to a pressure of ~26atm, the hydrogen storage capacity of the benzene moiety decorated (5, 5) SWNT is about 4.7wt.% and that of the pristine (5, 5) SWNT is nearly 3.9wt.%.
Structure of Multi-Species Charged-Particles with Competing Interactions in a Quadratic Trap
LIU Yan-Hong, CHEN Bao-Xin, WANG Long
Chin. Phys. Lett. 2006, 23 (6): 1540-1543 .  
Abstract   PDF(pc) (210KB) ( 403 )
Multi-species charged-particles interacting with each other by a competing short-range attraction and long-range repulsion potential confined in a quadratic trap are studied with molecular dynamics simulations. It is found that particles with similar mass-to-charge ratio tend to populate a common shell, whose location depends on the particle mass-to-charge ratio, and that the greater the latter is, the closer the particles to the centre of the trap are. This rule for the ground-state configuration is independent of the total particle and species numbers in the system.
Parametrically Driven Solitons in a Chain of Nonlinear Coupled Pendula with an Impurity
XU Hai-Qing, TANG Yi
Chin. Phys. Lett. 2006, 23 (6): 1544-1547 .  
Abstract   PDF(pc) (212KB) ( 554 )
The system consisting of a chain of parametrically driven and damped nonlinear coupled pendula with a mass impurity is studied by means of a discrete version of the envelope function approach. An analogue of the parametrically driven damped nonlinear Schödinger equation with an impurity term is derived from the original lattice equation. Analytical solutions of impurity pinned high-frequency breathers and kinks are obtained. The results show that the mass impurity has striking influence on the high-frequency modes. In addition, we perform numerical simulations, showing that the light mass impurity has a stabilizing effect on the chain. The breathers seeding chaos in the homogeneous chain are pinned on a suitable light impurity to pull the chain from the chaotic state.
Size-Dependent Melting Behaviour of Nanometre-Sized Pb Particles Studied by Dynamic Mechanical Analysis
CHEN Xiao-Ming, FEI Guang-Tao, CUI Ping
Chin. Phys. Lett. 2006, 23 (6): 1548-1550 .  
Abstract   PDF(pc) (184KB) ( 448 )
Nanometre-sized (hereafter nano-) Pb particles embedded in an Al matrix are prepared by ball milling. It is found that the size of nano-Pb particles was decreased with increasing milling time. The melting behaviour of nano-Pb particles embedded in the Al matrix is studied by means of dynamic mechanical analysis, and a single internal friction peak in the vicinity of Pb melting temperature is observed. The onset temperature of the peak moves to lower temperature with the decrease of particles size and the internal friction peak height is increased, which indicates a size-dependent melting behaviour of nano-Pb particles. It is suggested that the size-dependent melting behaviour is associated with surface melting.
Simulation of Temperature-Dependent Resistivity for Manganite La1/3Ca2/3MnO3
CAO Shuo, ZHOU Qing-Li, GUAN Dong-Yi, LU Hui-Bin, YANG Guo-Zhen
Chin. Phys. Lett. 2006, 23 (6): 1551-1553 .  
Abstract   PDF(pc) (264KB) ( 441 )
The resistivity of the heavy-doped La1/3Ca2/3MnO3 (LCMO) is simulated using a random resistor network model, based on a phase separation scenario. The simulated results agree well with the reported experimental data, showing a transition from a charge-disordered (CDO) state embedded with a few ferromagnetic (FM) metallic clusters to a charge-ordered (CO) state, corresponding to the transition from a high-temperature paramagnetic (PM) insulating state to a low-temperature antiferromagnetic (AF) insulating state. Furthermore, we find that the number of AF/CO clusters increases with decreasing temperature, and the clusters start to connect to each other around 250K, which causes percolating in the system. The results further verify that phase separation plays a crucial role in the electrical conductivity of LCMO.
Analysis of Frequency Spectrum of Laser-Induced Vibration of Microbeam Resonators
FANG Dai-Ning, SUN Yu-Xin, SOH Ai-Kah
Chin. Phys. Lett. 2006, 23 (6): 1554-1557 .  
Abstract   PDF(pc) (241KB) ( 434 )
The vibration phenomenon during pulsed laser heating of micro-beams is investigated. The beam is made of silicon and is heated by a laser pulse with a non-Gaussian temporal profile and with an ultrashort pulse duration of 2ps, which incites vibration due to the thermoelastic damping effect. This coupled thermoelastic problem is solved using an analytical--numerical technique based on the Laplace transformation. The damping ratio and resonant frequency shift ratio of beams due to the air damping effect and the thermoelastic damping effect are also examined and discussed.
Adsorption of L-Alanine on Cu(111) Studied by Scanning Tunnelling Microscopy
GE Si-Ping, Lü Chao, ZHAO Ru-Guang
Chin. Phys. Lett. 2006, 23 (6): 1558-1561 .  
Abstract   PDF(pc) (274KB) ( 518 )
The adsorption of L-alanine on Cu(111) surface is studied by means of scanning tunnelling microscopy under ultra-high vacuum conditions. The results show that the adsorbates are chemisorbed on the surface, and can form a two-dimensional gas phase, chain phase and solid phase, depending on deposition rate and amount. The adsorbed molecules can be imaged as individual protrusions and parallel chains in gas and chain phases respectively. It is also found that alanine can form (2×2) superstructure on Cu(111) and copper step facet to <110> directions in solid phase. On the basis of our scanning tunnelling microscopic images, a model is proposed for the Cu(111)(2×2)-alanine superstructure. In the model, we point out the close link between $\langle 110\rangle$-direction hydrogen bond chains with the same direction copper step faceting.
Modulation of Spin Distribution and Spin Transport by a Magnetic Field in a Quasi-One-Dimensional System with Spin--Orbit Coupling
LING Dong-Bo, XIA Ke, LI Ding-Ping, MA Zhong-Shui
Chin. Phys. Lett. 2006, 23 (6): 1562-1565 .  
Abstract   PDF(pc) (268KB) ( 402 )
The distributions of spin and currents modulated by magnetic field in a transverse parabolic confined two-dimensional electronic system with a Rashba spin--orbit coupling have been studied numerically. It is shown that the spin accumulation and the spin related current are generated by magnetic field if the spin--orbit coupling is presented. The distributions of charge and spin currents are antisymmetrical along the cross-section of confined system. A transversely applied electric field does not influence the characteristic behaviour of charge- and spin-dependent properties.
Giant Magnetoresistance in La0.67Ca0.33MnO3/Alq3/Co Sandwiched-Structure Organic Spin Valves
PANG Zhi-Yong, CHEN Yan-Xue, LIU Tian-Tian, ZHANG Yun-Pang, XIE Shi-Jie, YAN Shi-Shen, HAN Sheng-Hao
Chin. Phys. Lett. 2006, 23 (6): 1566-1569 .  
Abstract   PDF(pc) (240KB) ( 576 )
La0.67Ca0.33MnO3/Alq3/Co sandwiched-structure organic spin valves are fabricated by vacuum thermal evaporation method. A giant magnetoresistance (GMR) of 14% is observed at low temperature 100K. At 30K, the magnetoresistance can increase to 50%. The large GMR of the device is attributed to the high spin polarization and low conductivity of the La0.67Ca0.33MnO3 contact. The magnetoresistance ΔR/R and the coercive field of the Co electrode depend strongly on temperature. The large high-field magnetoresistance reported on La0.67Sr0.33MnO3/Alq3/Co organic spin valves [Nature 427 (2004) 821] is not observed in our La0.67Ca0.33MnO3/Alq2/Co organic spin valves.
Shot Noise in a Mesoscopic Interferometer
ZHANG Guang-Biao, WANG Shun-Jin, LI Lei
Chin. Phys. Lett. 2006, 23 (6): 1570-1573 .  
Abstract   PDF(pc) (248KB) ( 410 )
The charge conductance and the shot noise in an Aharonov--Bohm interferometer with double quantum dots embedded and coupled to each other by a capacity are studied in the framework of the equation of motion of Green’s function. From the impurity Anderson model Hamiltonian, the equations of motion of nonequilibrium Green functions are derived and solved including the effects of two body correlations under Lacroix’s approximation. Our results show that the conductance, the shot noise, and the Fano factor (the ratio of the shot noise to the Poisson noise) as functions of the magnetic flux oscillate with the period of h/e, and their oscillation behaviour is similar to the results of the experiment replacing the capacitive coupling by tunnelling between the two dots. The experiment is suggested to test the results.
Influence of Polarization-Induced Electric Field on Subband Structure in AlxGa1-xN/GaN Double Quantum Wells
LEI Shuang-Ying, SHEN Bo, ZHANG Guo-Yi
Chin. Phys. Lett. 2006, 23 (6): 1574-1577 .  
Abstract   PDF(pc) (213KB) ( 391 )
The influence of the polarization-induced electric field and other parameters on the subband structure in AlxGa1-xN /GaN coupled double quantum wells (DQWs) has been studied by solving the Schrödinger and Poisson equations self-consistently. It is found that the polarization effect leads to an asymmetric potential profile of AlxGa1-xN/GaN DQWs although the two wells have the same width and depth. The polarization effect also leads to a very large Stark shift between the odd and the even order subband levels that can reach 0.54eV. Due to the polarization-induced Stark shift, the wavelength of the intersubband transition between the first odd order and the second even order subband levels becomes smaller, which is useful for realization of optoelectronic devices operating within the telecommunication window region.
A Theoretic Approach to SU(4) Kondo Effect in Carbon Nanotube Quantum Dots
ZHU Rui
Chin. Phys. Lett. 2006, 23 (6): 1578-1580 .  
Abstract   PDF(pc) (222KB) ( 453 )
We propose a mean field approach to the transport properties of carbon nanotube quantum dots. Quantum interaction between spin and orbital pseudo-spin degrees of freedom results in an SU(4) Kondo effect at low temperatures. By calculating the chemical potentials and the tunnelling strengths, and hence the spectral functions for different coupling constants and applied magnetic fields, we find that this exotic Kondo effect manifests as a four-peak splitting in the non-linear conductance when an axial magnetic field is applied.
Electronic Structure and Magnetic Properties of SmCo7-xZrx
ZHANG Chang-Wen, LI Hua, DONG Jian-Min, GUO Yong-Quan, LI Wei
Chin. Phys. Lett. 2006, 23 (6): 1581-1584 .  
Abstract   PDF(pc) (228KB) ( 448 )
The electronic structure and magnetism of SmCo7-xZrx alloy are investigated using the spin-polarized MS-X. method. The results show that a few of electrons are transferred to the Sm(5d0) orbital due to orbital hybridization between Sm and Co atoms. The exchange interactions between 3d and 5d electrons are more important than the polarization effects of the conductive electrons, thus it is the main reason resulting in the long-range ferromagnetic order in SmCo7-xZrx. The Curie temperature of SmCo7-xZrx is generally lower than that of corresponding pure Co, which may be explained by the weaker average coupling strength between Co lattices due to some negative couplings mainly occurring of 2e site. The calculated results for the Sm5Co32Zr2 cluster may lead to a better understanding of why SmCo7-xZrx is stable phase. Since the spin-up DOS peak of d electrons at EF arises and the bonding of electrons at EF strengthens with increasing Zr concentration, which results in the internal energy of the system decrease, the stable ferromagnetic order forms in SmCo7-xZrx.

Influence of Mn-Doped Content on Ferromagnetism of Ga1-xMnxN Film Grown by LP-MOVPE
ZHANG Bin, YAO Shu-De, WANG Kun, DING Zhi-Bo, CHEN Zhi-Tao, SU Yue-Yong, ZHANG Guo-Yi, MA Hong-Ji, NIE Rui, ZHANG Ya-Wei
Chin. Phys. Lett. 2006, 23 (6): 1585-1587 .  
Abstract   PDF(pc) (230KB) ( 439 )
The diluted magnetic semiconductor Ga1-xMnxN was achieved by low-pressure metal organic vapour-phase epitaxy (LP-MOVPE). Proton-induced x-ray emission was employed non-destructively, quickly and accurately to determine the Mn-doped content. The magnetic property was measured by a superconducting-quantum-interference-device (SQID) magnetometer. Apparent ferromagnetic hysteresis loops measured at or above room temperature are presented. No ferromagnetic secondary phases were detected by high-resolution x-ray diffraction. The experimental results show that the ferromagnetic signal firstly decreases and then increases with the increasing Mn-doped content from 0.23% to 4.69% and it is the weakest when Mn content is 0.51%. The annealing treatment could make the ferromagnetic property stronger.
Electronic States and Spatial Charge Distribution of Single Mn Impurity in Diluted Magnetic Semiconductors
WANG Wei-Hua, ZOU Liang-Jian
Chin. Phys. Lett. 2006, 23 (6): 1588-1591 .  
Abstract   PDF(pc) (225KB) ( 438 )
The electronic and magnetic properties as well as the spatial charge distribution of single Mn impurity in III--V diluted magnetic semiconductors are obtained when the degeneracy of the p orbits contributed from the four nearest-neighbouring As(N) atoms is taken into account. We show that in the ground state, the Mn spin is strongly antiferromagnetically coupled to the surrounding As(N) atoms when the p-d hybridization Vpd is large and both the hole level Ev and the impurity level Ed are close to the Fermi energy. The spatial charge distribution of the Mn acceptor in the (110) plane is non-spherically symmetric, in good agreement with the recent STM images.
Low-Temperature Magnetic Properties of Co Antidot Array
LIU Qing-Fang, JIANG Chang-Jun, FAN Xiao-Long, WANG Jian-Bo, XUE De-Sheng
Chin. Phys. Lett. 2006, 23 (6): 1592-1595 .  
Abstract   PDF(pc) (204KB) ( 661 )
Cobalt antidot arrays with different thicknesses are fabricated by rf magnetron sputtering onto porous alumina substrates. Scanning electron microscopy and grazing incidence x-ray diffraction are employed to characterize the morphology and crystal structure of the antidot array, respectively. The temperature dependence of magnetic properties shows that in the temperature range 5K--300K, coercivity and squareness increase firstly, reach their maximum values, then decrease. The anomalous temperature dependences of coercivity and squareness are discussed by considering the pinning effect of the antidot and the magnetocrystalline anisotropy.
Field-Induced Domain Reorientation and Polarization Rotation of <110> Oriented Pb(Mg1/3Nb2/3)O3-PbTiO3 Single Crystals
CHEN Ke-Pi, ZHANG Xiao-Wen, FANG Fei
Chin. Phys. Lett. 2006, 23 (6): 1596-1599 .  
Abstract   PDF(pc) (246KB) ( 478 )
Polarization hysteresis loops, x-ray diffraction and temperature dependent dielectric constant under different electric fields for <110> oriented 0.7PMN-0.3PT crystals are measured. The field-induced phase transition and the process of depolarization are discussed. The results show that with the electric field E increasing, the single-crystal form changes from the relaxor state of rhombohedral to normal rhombohedral, then to a monoclinic state via polar-axis reorientation and polarization rotation. Orthorhombic phase may present when E≥10kV, but it is an unstable form after E removal. The depolarization process is not just the reversal of the polarization process. It is noticed that only the temperature-dependent dielectric behaviour is not enough to judge the processes of the E-field induced phase transition.
Ultra-Compact, Subwavelength and Single-Mode Cavity Resonator
SHEN Yi-Feng, XU Chun, TANG Yun-Fei, LIU Xiao-Han, ZI Jian, CHEN Hong
Chin. Phys. Lett. 2006, 23 (6): 1600-1602 .  
Abstract   PDF(pc) (231KB) ( 527 )
We propose an ultra-compact subwavelength cavity resonator that is composed of a bilayer of metamaterials, one with only negative dielectric constant and the other one with only negative permeability. It is shown that the total thickness of the resonator can be much smaller than the resonant wavelength. In addition, this resonator is always single-mode.
Diffuse Backscattering Mueller Matrices Patterns from Turbid Media
ZHANG Lian-Shun, ZHU Chen, WANG Zhi-Ping, ZHANG Jing
Chin. Phys. Lett. 2006, 23 (6): 1603-1606 .  
Abstract   PDF(pc) (91KB) ( 426 )
We present experimental measurements and theory of the diffusely backscattered Mueller matrix patterns that arise from illuminating a turbid medium with a polarized laser beam. Our technique employs polarized light from a He--Ne laser (λ =632.8 nm) focused onto the surface of the scattering medium. A surface area of approximately 2×2cm2 centred on the light input point is imaged through polarization analysis optics onto a CCD camera. The Mueller matrix is reconstructed by 49 intensity measurements with various
orientations of polarizer and analyser. The measured Mueller matrix of polystyrene spheres is compared with the theory result of incoherent scattering of light by spheres. It shows that the azimuthal patterns of the Mueller matrix are determined by the symmetry of the turbid media and the shape of scattering particles. The result is further proved by experiments with polystyrene spheres of different concentrations in de-ionized water.
Diffuse Backscattering Mueller Matrices Patterns from Turbid Media
ZHANG Lian-Shun, ZHU Chen, WANG Zhi-Ping, ZHANG Jing
Chin. Phys. Lett. 2006, 23 (6): 1603-1606 .  
Abstract   PDF(pc) (1342KB) ( 465 )
We present experimental measurements and theory of the diffusely backscattered Mueller matrix patterns that arise from illuminating a turbid medium with a polarized laser beam. Our technique employs polarized light from a He-Ne laser (λ=632.8nm) focused onto the surface of the scattering medium. A surface area of approximately 2×2 cm2 centred on the light input point is imaged through polarization analysis optics onto a CCD camera. The Mueller matrix is reconstructed by 49 intensity measurements with various orientations of polarizer and analyser. The measured Mueller matrix of polystyrene spheres is compared with the theory result of incoherent scattering of light by spheres. It shows that the azimuthal patterns of the Mueller matrix are determined by the symmetry of the turbid media and the shape of scattering particles. The result is further proved by experiments with polystyrene spheres of different concentrations in de-ionized water.
Electroluminescence of a Multi-Layered Organic Light-Emitting Diode Utilizing Trans-4-[p-[N-methyl-N-(hydroxymethyl)amino]styryl]-N-Methylphridinium Tetraphenylborate as the Active Layer
FENG Xue-Yuan, ZHANG Jia-Yu, XU Chun-Xiang, QIAO Yi, CUI Yi-Ping
Chin. Phys. Lett. 2006, 23 (6): 1607-1609 .  
Abstract   PDF(pc) (192KB) ( 481 )
Employing an organic dye salt of trans-4-[p-[N-methyl-N-(hydroxymethyl)amino]styryl]-N-methylphridinium tetra\-phenylborate (ASPT) as the active layer, 8-hydrocyquinoline aluminium (Alq3) as the electron transporting layer and N,N’-diphenyl-N,N’-bis(3-methylphenyl)-[1,1’-biphenyl]-4,4’-diamine (TPD) as the hole transporting layer, respectively, we fabricate a multi-layered organic light-emitting diode and observe the colour tunable electroluminescence (EL). The dependence of the EL spectra on the applied voltage is investigated in detail, and the recombination mechanism is discussed by considering the variation of the hole-electron recombination region.
Structural and Optical Properties of Nanocrystal In2O3 Films by Thermal Oxidation of In2S3 Films
M. Ö, ztas, M. Bedir, Z. Ö, ztürk, D. Korkmaz, S. Sur
Chin. Phys. Lett. 2006, 23 (6): 1610-1012 .  
Abstract   PDF(pc) (197KB) ( 686 )
In2S3 nanocrystalline films are prepared on glass substrates by the spray pyrolysis technique using indium chloride and thiourea as precursors. The deposition is carried out at 350°C on glass substrates. The films are then annealed for two hour at 200, 400, 600, and 800°C in O2 flow. This process allows the transformation of nanocrystal In2O3 films from In2S3 films and the reaction completes at 600°C. These results indicate that the In2O3 film prepared by this simple thermal oxidation method is a promising candidate for electro-optical and photovoltaic devices.
Theoretical Study on Absorption of Magnetically Tunable Terahertz Quantum-Well Photodetectors
CHEN Yu-Ling, GUO Xu-Guang, CAO Jun-Cheng
Chin. Phys. Lett. 2006, 23 (6): 1613-1615 .  
Abstract   PDF(pc) (223KB) ( 467 )
Because of the Zeeman splitting effect in diluted semiconductor (Zn,Cd,Mn)Se, the absorption spectrum of ZnSe/(Zn,Cd,Mn)Se quantum wells can be adjusted by magnetic field effectively. Within the effective-mass approximation, the conduction electronic structure and the absorption spectrum of ZnSe/(Zn,Cd,Mn)Se quantum wells subjected to in-plane magnetic fields are investigated. Our theoretical results show that it is possible to use the ZnSe/(Zn,Cd,Mn)Se quantum well as magnetically tunable terahertz photodetectors.
Analytic Solution of Charge Density of Single Wall Carbon Nanotube under Conditions of Field Electron Emission
LI Zhi-Bing, WANG Wei-Liang
Chin. Phys. Lett. 2006, 23 (6): 1616-1618 .  
Abstract   PDF(pc) (188KB) ( 455 )
We derive the analytic solution of induced electrostatic potential along single wall carbon nanotubes. Under the hypothesis of constant density of states in the charge-neutral level, we are able to obtain the linear density of excess charge in an external field parallel to the tube axis.
Growth of Strain Free GaN Layers on (0001) Oriented Sapphire by Using Quasi-Porous GaN Template
XIE Xin-Jian, ZHONG Fei, QIU Kai, LIU Gui-Feng, YIN Zhi-Jun, WANG Yu-Qi, LI Xin-Hua, JI Chang-Jian, HAN Qi-Feng, CHEN Jia-Rong, CAO Xian-Cun
Chin. Phys. Lett. 2006, 23 (6): 1619-1622 .  
Abstract   PDF(pc) (230KB) ( 649 )
We report the reduced-strain gallium-nitride (GaN) epitaxial growth on (0001) oriented sapphire by using quasi-porous GaN template. A GaN film in thickness of about 1μm was initially grown on a (0001) sapphire substrate by molecular beam epitaxy. Then it was dealt by putting into 45% NaOH solution at 100°C for 10min. By this process a quasi-porous GaN film was formed. An epitaxial GaN layer was grown on the porous GaN layer at 1050°C in the hydride vapour phase epitaxy reactor. The epitaxial layer grown on the porous GaN is found to have no cracks on the surface. That is much improved from many cracks on the surface of the GaN epitaxial layer grown on the sapphire as the same as on GaN buffer directly.
Variability on Raman Shift to Stress Coefficient of Porous Silicon
LEI Zhen-Kun, KANG Yi-Lan, CEN Hao, HU Ming
Chin. Phys. Lett. 2006, 23 (6): 1623-1626 .  
Abstract   PDF(pc) (203KB) ( 553 )
Porous silicon film is a capillary-like medium, which is able to reveal different meso-elastic modulus with porosity. During the preparation of porous silicon samples, the capillary force is a non-classic force related to the liquid evaporation which directly influences the evolution of residual stress. In this study, a non-linear relation of Raman shift to stress coefficient and the porosity is obtained from the elastic modulus measured with nano-indentation by Bellet et al. [J. Appl. Phys. 60 (1996) 3772] Dynamic capillarity during the drying process of porous silicon is investigated using micro-Raman spectroscopy, and the results reveal that the residual stress resulted from the capillarity increased rapidly. Indeed, the dynamic capillarity has a close relationship with a great deal of micro-pore structures of the porous silicon.
Growth of Indium Nanorods by Magnetron Sputtering
WEI He-Lin, HUANG Han-Chen, ZHANG Xi-Xiang
Chin. Phys. Lett. 2006, 23 (6): 1627-1630 .  
Abstract   PDF(pc) (304KB) ( 538 )
Indium nanorods are grown on silicon substrates by using magnetron-sputtering technique. Film morphologies and nanorod microstructure are investigated by using scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), and x-ray diffraction. It is found that the mean diameter of the nanorods ranges from 30nm to 100nm and the height ranges from 30nm to 200nm. The HRTEM investigations show that the indium nanorods are single crystals and grow along the [100] axis. The nanorods grow from the facets near the surface undulation that is caused by compressive stress in the indium grains generated during grain coalescence process. For low melting point and high diffusivity metal, such as bismuth and indium, this spontaneous nanorod growth mechanism can be used to fabricate nanostructures.
Dielectric Properties of Fine-Grained BaTiO3 Ceramics under High Pressure
ZHU Jin-Long, XIAO Chang-Jiang, CHI Zhen-Hua, FENG Shao-Min, LI Feng-Ying, JIN Chang-Qing, DENG Xiang-Yun, WANG Xiao-Hui, LI Long-Tu, DAI Zhong-Hua, WANG Jun, XU Zhuo
Chin. Phys. Lett. 2006, 23 (6): 1631-1633 .  
Abstract   PDF(pc) (263KB) ( 463 )
We investigate the temperature dependence of the dielectric constant of BaTiO3 ceramic with coarse to nano-grain size under different hydrostatic high pressures up to 5000bar in the range between room temperature and 200°C. The ferroelectric-to-paraelectric phase transition temperatures Tc are determined from the peak of dielectric constant versus temperature. The values of average grain-size are estimated from the SEM images. It is found that the magnitude of dTc/dp varies considerably from sample to sample depending on grain size. The Curie point Tc of the sample with small grain size decreases more sharply than that of samples with larger one.
Experimental Study on Physical Mechanism of Drag Reduction of Hydrophobic Materials in Laminar Flow
YU Yong-Sheng, WEI Qing-Ding
Chin. Phys. Lett. 2006, 23 (6): 1634-1637 .  
Abstract   PDF(pc) (226KB) ( 742 )
We experimentally study the physical mechanism of the drag reduction of hydrophobic materials in the macroscopic scale. The experiment includes the drag and velocity measurements of laminar boundary layer flow over flat plates, and the observation of air bubbles on the surfaces. The plate surfaces have different wetting and roughness properties. In the drag measurements, the plates with bubbles on the surfaces lead to drag reduction, but not for those without bubbles. Velocity measurement confirms that the flow is laminar and gives apparent fluid slip on the plate wall with bubbles. In observation, air bubbles in macroscopic size emerge and enlarge on hydrophobic surfaces but not on hydrophilic surfaces. Therefore, the drag reduction of
hydrophobic materials is explained by the generation of air bubbles of macroscopic size that cause the apparent velocity slip.
Fabrication of c-Si:H(p)/c-Si(n) Heterojunction Solar Cells with Microcrystalline Emitters
ZHOU Bing-Qing, LIU Feng-Zhen, ZHANG Qun-Fang, XU Ying, ZHOU Yu-Qin, LIU Jin-Long, ZHU Mei-Fang
Chin. Phys. Lett. 2006, 23 (6): 1638-1640 .  
Abstract   PDF(pc) (223KB) ( 645 )
The p-type microcrystalline silicon (μc-Si:H) on n-type crystalline silicon (c-Si) heterojunction solar cells is fabricated by radio-frequency plasma enhanced chemical vapour deposition (rf-PECVD). The effect of the μc-Si:H p-layers on the performance of the heterojunction solar cells is investigated. Optimum μc-Si:H p-layer is obtained with hydrogen dilution ratio of 99.65%, rf-power of 0.08W/cm2, gas phase doping ratio of 0.125%, and the p-layer thickness of 15nm. We fabricate μc-Si:H(p)/c-Si(n) heterojunction solar cells without texturing and obtained an efficiency of 13.4%. The comparisons of the solar-cell performances using different surface passivation techniques are discussed.
Vibrations in Magnet/Superconductor Levitation Systems
F. Y. Alzoubi, H. M. Al-khateeb, M. K. Alqadi, N. Y. Ayoub,
Chin. Phys. Lett. 2006, 23 (6): 1641-1644 .  
Abstract   PDF(pc) (184KB) ( 507 )
The problem of a small magnet levitating above a very thin superconducting disc in the Meissner state is analysed. The dipole--dipole interaction model is employed to derive analytical expressions for the interaction energy, levitation force, magnetic stiffness and frequency of small vibrations about the equilibrium position in two different configurations, i.e. with the magnetic moment parallel and perpendicular to the superconductor. The results show that the frequency of small vibrations decreases with the increasing levitation height for a particular radius of the superconducting disc, which is in good agreement with the experimental results. However, the frequency increases monotonically up to saturation by increasing the radius of the disc for a particular height of the magnet. In addition, the frequency of vibrations is higher when the system is in the vertical configuration than that when the system is in the horizontal configuration.
Preparation and Raman Spectrum of Rutile Single Crystals Using Floating Zone Method
GUO Xing-Yuan, XU Da-Peng, DING Zhan-Hui, SU Wen-Hui,
Chin. Phys. Lett. 2006, 23 (6): 1645-1647 .  
Abstract   PDF(pc) (193KB) ( 1022 )
With anatase-type titanium dioxide as the raw materials, the rutile type titanium dioxide single crystal is prepared using the floating zone method. The results of XRD measurement show that the grown crystal is highly crystalline with a rutile structure, which has orientation to the c-axis. The four Raman vibration characteristic peaks (143, 240, 450 and 610cm-1) at room temperature show that the crystalline structure of the single crystal is a typical rutile phase, meanwhile a new Raman peak at around 690cm-1 is found. The results of the Raman measurement at various temperatures for the single crystal show that the Raman frequency shifts are different.
Geodesics of Spherical Dilaton Spacetimes
ZENG Yi, Lü Jun-Li, WANG Yong-Jiu
Chin. Phys. Lett. 2006, 23 (6): 1648-1651 .  
Abstract   PDF(pc) (234KB) ( 435 )
The properties of spherical dilaton black hole spacetimes are investigated through a study of their geodesics. The closed and non-closed orbits of test particles are analysed using the effective potential and phase-plane method. The stability and types of orbits are determined in terms of the energy and angular momentum of the test particles. The conditions of the existence of circular orbits for a spherical dilaton spacetime with an arbitrary dilaton coupling constant α are obtained. The properties of the orbits and in particular the position of the innermost stable circular orbit are compared to those of the Reissner--Nordström spacetime. The circumferential radius of innermost stable circular orbit and the corresponding angular momentum of the test particles increase for α≠0.
Fusion Reaction of 16O+14N and Its Implication for the Production of 26Al in Explosive Oxygen Burning
WANG Peng, PENG Qiu-He, , ZHANG Shui-Nai, LUO Xin-Lian
Chin. Phys. Lett. 2006, 23 (6): 1652-1654 .  
Abstract   PDF(pc) (209KB) ( 431 )
We suggest that the fusion reaction 16O+14N may be a new way to produce 26Al in interstellar medium. Adopting different mixing modes, we investigate the impact on the production of 26Al in explosive oxygen burning and find that the result is extremely sensitive to mixing mechanisms. In some cases, we obtain an encouraging result, for example, the greatest final abundance of 26Al reaches 7.779×10-6, which means that the explosive oxygen burning may be a new origin of 26Al.
A Parametric Dynamic Model of Dark Energy
DENG Xue-Mei, WU Ya-Bo, ZHAO Guo-Ming
Chin. Phys. Lett. 2006, 23 (6): 1655-1658 .  
Abstract   PDF(pc) (209KB) ( 611 )
The double complex symmetric gravitational theory is extended to the parametric symmetric gravitational theory by introducing a parameter β. Hence parametric Friedmann--Robertson--Walker equations are obtained and some characters of dark energy in corresponding spaces are discussed by taking different values of β. In our method some previous results can be included as the special case of our results. It is worth noting that some characters of dark energy can be more intuitively described in our model. By analysis, we can predict that the fate of universe would be a Big Rip in the future, and also find that the state parameters for the two different constraint conditions ωФ are consistent with the present cosmological observations.
84 articles