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Volume 23 Issue 9
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Original Articles
Grammian Solutions to a Non-Isospectral Kadomtsev--Petviashvili Equation
Chin. Phys. Lett. 2006, 23 (9): 2349-2351 .  
Abstract   PDF(pc) (194KB) ( 605 )
Solutions in the Grammian form for a non-isospectral Kadomtsev--Petviashvili equation are derived by means of Pfaffian derivative formulae. Explicit entries of the Grammian are given. Non-isospectral dynamics of the solutions generated from the Grammian are investigated in an analytic way. The solutions obtained can describe line solitons in non-uniform media travelling with time-dependent amplitude and time-dependent direction. In addition, some other solutions have singularities.
Block Entanglement in the Single-Hole Hubbard Model
YAO Kai-Lun, SUN Xiao-Zhong, LIU Zu-Li, LI Yan-Chao, YU Li, GAO Guo-Ying
Chin. Phys. Lett. 2006, 23 (9): 2352-2355 .  
Abstract   PDF(pc) (275KB) ( 550 )
We investigate the distribution of the entanglement of the one-dimensional single-hole Hubbard model (HM) and study the relationship between the entanglement and quantum phase transition in the model. The von Neumann entropy of a block with neighbouring spins L for a single-hole HM is calculated using the density-matrix renormalization group. The distributions of the entanglement entropy in the ground state, as a function of block length, show a dramatic effect, i.e. effectively decoupling with the centres, no matter how the Coulomb interaction u>0 or u<0. Contrarily, for the Coulomb interaction u=0 or close to zero, the entanglement entropy in the single-hole model reaches a saturation value for a certain block size. For a fixed size L=40, the ground state entanglement entropy measure, as a function of u, shows a peak corresponding to the critical quantum phase transition.
Teleportation of Quantum States through Mixed Entangled Pairs
ZHENG Shi-Biao
Chin. Phys. Lett. 2006, 23 (9): 2356-2359 .  
Abstract   PDF(pc) (187KB) ( 1047 )
We describe a protocol for quantum state teleportation via mixed entangled pairs. With the help of an ancilla, near-perfect teleportation might be achieved. For pure entangled pairs, perfect teleportation might be achieved with a certain probability without using an ancilla. The protocol is generalized to teleportation of multiparticle states and quantum secret sharing.

Multiparty Simultaneous Quantum Identity Authentication Based on Entanglement Swapping
WANG Jian, ZHANG Quan, TANG Chao-Jing
Chin. Phys. Lett. 2006, 23 (9): 2360-2363 .  
Abstract   PDF(pc) (209KB) ( 766 )
We present a multiparty simultaneous quantum identity authentication protocol based on entanglement swapping. In our protocol, the multi-user can be authenticated by a trusted third party simultaneously.
Neural Signal Tuned by Random Long-range Connections in Coupled FitzHugh--Nagumo Neurons Systems
ZHANG Ji-Qian, HOU Zhong-Huai, XIN Hou-Wen
Chin. Phys. Lett. 2006, 23 (9): 2364-2367 .  
Abstract   PDF(pc) (293KB) ( 557 )
We investigate the effect of random long-range connections on signal propagation in an array of coupled FitzHugh--Nagumo (FHN) neurons. The neural network can be obtained by randomly adding a small fraction of shortcuts in an originally locally coupled one-dimensional chain. It is shown that when the first neuron is subjected to external stimuli, it fires and excites its connected neighbours, such that the neural signal may propagate along the chain favoured by the shortcuts. Moreover, there exists an optimal number of shortcuts which can lead to the most synchronous behaviour. In addition, how the region of the fraction of shortcuts varies with the coupling strength is also discussed. These results suggest that topological disorder in the neural network may play a vital role in helping information processing in living systems.

Monte Carlo Study on Focus Properties of Portable Ultrabright Microfocus X-Ray Sources
WANG Kai-Ge, WANG Lei, LIU Wen-Qing, NIU Han-Ben
Chin. Phys. Lett. 2006, 23 (9): 2368-2371 .  
Abstract   PDF(pc) (288KB) ( 667 )
The construct and electrode potential of emitting systems are very important for the portable ultrahigh brightness microfocus x-ray sources. The ratio of Dw/H (Dw is the diameter of Wehnelt grid aperture and H is the setting height of the cathode) and the grid bias are determinative parameters for the emission current and focus properties of an electron beam. The Monte Carlo method is used to numerically calculate the electron beam trajectories within a microfocus x-ray tube. The calculated results indicate that an optimum source system with the electron beam focal spot diameter smaller than 10μm at the anode, reasonable short focal length of about 76mm and the cathode emission current of more than 30mA can be attained under conditions of Dw/H =5 and grid bias Vg= -0.6kV.
Temperature Tuning of Casimir Effect
WANG Jing, ZHANG Xiang-Dong, PEI Shou-Yong, LIU Da-He
Chin. Phys. Lett. 2006, 23 (9): 2372-2375 .  
Abstract   PDF(pc) (223KB) ( 491 )
We theoretically investigate the additional correction to the Casimir effect due to the change of dielectric constant with temperature, which is different from the previous research that have widely taken dielectric constants of materials as a value independent of temperature. It is found that such a correction can go beyond 20% for some cases and it should not be ignored. Due to the prominent correction, it is possible to tune the Casimir force by such an effect.
Radiative Decays of Charmonium into Light Mesons
GAO Ying-Jia, ZHANG Yu-Jie, CHAO Kuang-Ta
Chin. Phys. Lett. 2006, 23 (9): 2376-2378 .  
Abstract   PDF(pc) (245KB) ( 505 )
We apply perturbative QCD to the radiative decays of charmonia J/ψ and XcJ into light mesons. We perform a complete numerical calculation for the quark--gluon loop diagrams involved in these processes. The calculated J/ψ decay branching ratios into p-wave mesons f2(1270) and f1(1285) fit the data well, while that of f0(980) (if treated as an ss meson) is predicted to be 1.6×10-4, which implies that f0(1710) can not be the ss or (uu+dd)√2 meson. Decays of p-wave charmonia XcJ → ρ (ω,Ф) γ (J=0,1,2) are also studied, and the branching ratio of Xcl → ρ γ is predicted to be 1.4×10-5, which may be tested by CLEO-c ollaboration and BESIII collaboration with future experiments.
Littlest Higgs Model and Spin Correlation of Top Quark Production at High Energy Linear e+ e- Colliders
YUE Chong-Xing, WANG Lei, WANG Li-Na, ZHANG Yan-Ming
Chin. Phys. Lett. 2006, 23 (9): 2379-2382 .  
Abstract   PDF(pc) (259KB) ( 368 )
Based on the littlest Higgs model, we investigate the spin correlation of the top quark pair production via the process e+ e- → tt at the high energy linear e+ e- collider (ILC) with a centre-of-mass energy √S=800GeV. Our numerical results show that the gauge boson ZH generates very small corrections to the spin correlation observable C in all the parameter space allowed by the electroweak data. However, with reasonable values of the free parameters, the value of the relative correction parameter R’BH=(CBH-CSM)/CSM can reach 10%, which might be detected in future ILC experiments.
Proton Spin Structure Functions and Quark--Hadron Duality
DONG Yu-Bing
Chin. Phys. Lett. 2006, 23 (9): 2383-2386 .  
Abstract   PDF(pc) (223KB) ( 390 )
Quark--hadron duality of three proton spin structure functions g1, g2 and gT are discussed simultaneously. It is found that the onsets of the quark--hadron dualities of g1p, g2p and gTp are similar and they are expected to be at about Q2 ~ 2GeV2. In addition, our results show that the elastic peak remarkably breaks local quark--hadron duality.
Finite-Width Correction to Form Factors of γγ→ π0 Transition
HANG Sheng-Xi, ZHANG Zhen-Yu, LIU Jue-Ping
Chin. Phys. Lett. 2006, 23 (9): 2387-2390 .  
Abstract   PDF(pc) (239KB) ( 513 )
Instead of the usual zero-width approximation for one resonance, we use the finite-width approximation for the two low resonances, i.e. the ρ-ω mesons, to investigate the light-cone local QCD sum rules for the form factor of the transition γγ→ π0. According to the method of the analytic continuation by duality, the weight function, the polynomial of a low order N, is added to the dispersion integral to annihilate the integrand in the region where both resonance saturation and the QCD asymptotic expression are least reliable. The resultant form factor in the cases for the zero- and finite-widths are almost the same, both agree well with the experimental measurements. A comparison with the result from the Laplacian transformed light-cone sum rules and a brief discussion are given.
Resonance Conversion as a Catalyzer of Nuclear Reactions
Chin. Phys. Lett. 2006, 23 (9): 2391-2394 .  
Abstract   PDF(pc) (225KB) ( 506 )
It is shown that resonance internal conversion offers a feasible tool for mastering nuclear processes with laser or synchrotron radiation. The physics of the process is discussed in detail in a historical aspect. Possible experimental application is shown in the case of the M1 70.6-keV transition in nuclei of 169Yb. The nuclear transition rate in hydrogen-like ions of this nuclide can be enhanced by up to four orders of magnitude.
Fusion Hindrance Factor of Heavy Nuclei Extracted from Experimental Data
LIU Zu-Hua, ZHOU Hong-Yu
Chin. Phys. Lett. 2006, 23 (9): 2395-2398 .  
Abstract   PDF(pc) (246KB) ( 411 )
The reactions of 16O+204Pb, 82Se+138Ba and 96Zr+124Sn lead to the same compound nucleus 220Th. In terms of the assumption that the surviving probability is independent of entrance channel, we have extracted the fusion hindrance factor from the evaporation residue cross sections for the reactions of 82Se+138Ba and 96Zr+124Sn and compared with the results calculated using a two-parameter Smoluchowski equation. The theoretical predictions are basically in agreement with the experimental data. It is found that the probability of forming a compact 220Th is less than 10% for the reactions considered. For the systems more massive than 220Th, fusion should be much more strongly suppressed due to the competition of quasifission with complete fusion. Understanding of this inhibition is essential to forming new superheavy nuclei.
Energy Loss of Charm Quark Observed via Dimuon Production in Pb--Pb Collisions at √ snn=5.5 TeV
DING Heng-Tong, ZHOU Dai-Cui, YIN Zhong-Bao
Chin. Phys. Lett. 2006, 23 (9): 2399-2302 .  
Abstract   PDF(pc) (258KB) ( 469 )
Based on the HVQMNR model of heavy flavour production and the BDMPS approach on parton energy loss, we have investigated the energy loss effect of charm quark on (di)muon spectra in forward rapidity region covered by ALICE forward muon spectrometer in Pb+Pb collisions at c.m. energy √ snn=5.5 TeV. Results show that (di)muon spectra are very sensitive to the charm quark energy loss and can provide valuable information on the energy loss of heavy flavours.
B-Spline with Symplectic Algorithm Method for Solution of Time-Dependent Schrödinger Equations
BIAN Xue-Bin, QIAO Hao-Xue, SHI Ting-Yun
Chin. Phys. Lett. 2006, 23 (9): 2403-2406 .  
Abstract   PDF(pc) (249KB) ( 748 )
A B-spline with the symplectic algorithm method for the solution of time-dependent Schrödinger equations (TDSEs) is introduced. The spatial part of the wavefunction is expanded by B-spline and the time evolution is given in a symplectic scheme. This method allows us to obtain a highly accurate and stable solution of TDSEs. The effectiveness and efficiency of this method is demonstrated by the high-order harmonic spectra of one-dimensional atoms in comparison with other references.
Infrared Spectroscopic Analysis of Chrysene and 1.2-Benzanthracence in Wax films
Md. Naziruddin Khan, A. S. Al-Dwayyan, Z. H. Zaidi
Chin. Phys. Lett. 2006, 23 (9): 2407-2410 .  
Abstract   PDF(pc) (191KB) ( 774 )
Chrysene and 1.2-benzanthracene are successfully doped in a solid wax film and their vibrational spectra in 2000--400cm-1 are discussed. The harmonic frequencies and relative intensities of both the molecules observed in the film are compared with theoretical values calculated by the density functional theory (DFT) model as well as with the previous experimental data. The effects on spectra due to change of matrix and some additional bands observed in the wax film are also reported. Excellent agreement in the spectral positions and strengths between the experiments and DFT values are found
Propagation Effect of Hollow Gaussian Beams Passing through a Misaligned Optical System
ZHAO Cheng-Liang, WANG Li-Gang, LU Xuan-Hui, WANG Yu-Zhu
Chin. Phys. Lett. 2006, 23 (9): 2411-2414 .  
Abstract   PDF(pc) (375KB) ( 382 )
A generalized formula of hollow Gaussian beams through the first-order misaligned ABCD systems is derived by using the generalized diffraction integral formula. It is shown that the hollow Gaussian beam passing through the misaligned system becomes a decentred hollow Gaussian beam. The propagation properties of the output beam are investigated when it propagates through a simple misaligned lens system. These results provide a powerful theoretical tool for applications of optical traps.
High Resolution and High Sensitivity Measurement of Methane at 1.51μm
DENG Lun-Hua, GAO Xiao-Ming, CAO Zhen-Song, ZHAO Wei-Xiong, ZHANG Wei-Jun
Chin. Phys. Lett. 2006, 23 (9): 2415-2417 .  
Abstract   PDF(pc) (231KB) ( 470 )
The high-resolution absorption spectrum of CH4 at 1.51μm is observed by direct absorption spectroscopy technique with a White absorption cell. Multi-peak fitting technique is adopted to reveal line positions and line intensities of CH4 from 6608cm-1 to 6625cm-1. Special attention is paid on the determination of the line positions, and the accuracy is better than ±0.002cm-1. A minimum measurable absorption of 2.1×10-8 (3σ) has been achieved based on the measured direct absorption spectroscopy.
Experimental Study of Single and Double Electron Detachment Cross Sections for Cl- in Collision with He
YANG En-Bo, GAO Mei, HUANG Yong-Yi, WU Shi-Min, LI Guang-Wu, ZHANG Xue-Mei, LU Fu-Quan
Chin. Phys. Lett. 2006, 23 (9): 2418-2421 .  
Abstract   PDF(pc) (229KB) ( 352 )
Single-electron detachment (SED) and double-electron detachment (DED) for chlorine negative ions in collision with helium are investigated in the energy region of 5--30keV (SED) and 5--19keV (DED) by growth rate method, respectively. Experimental data from this work are compared with the previous reported data, and a general discussion is given.
Superluminal Behaviour of Modified Bessel Waves
WANG Zhi-Yong, XIONG Cai-Dong
Chin. Phys. Lett. 2006, 23 (9): 2422-2425 .  
Abstract   PDF(pc) (210KB) ( 490 )
Much experimental evidence of superluminal phenomena has been available by electromagnetic wave propagation experiments, with the results showing that the phase time describes the barrier traversal time. Based on the extrapolated phase time approach and numerical methods, we show that, in contrast to the ordinary Bessel waves of real argument, the group velocities of modified Bessel waves are superluminal. We obtain the following results. The group velocities increase with the increase of propagation distance, which is similar to the evanescent plane-wave cases. For large wave numbers, the group velocities fall off as the wave numbers increase, which is similar to the evanescent plane-wave cases. For small wave numbers, the group velocities increase with the increase of wave numbers, this is different from the evanescent plane-wave cases.
Direct Solution of the Inverse Problem for Rough Surface Scattering
REN Yu-Chao, GUO Li-Xin, WU Zhen-Sen
Chin. Phys. Lett. 2006, 23 (9): 2426-2429 .  
Abstract   PDF(pc) (555KB) ( 423 )
We consider the inverse scattering problem for a scalar wave field incident on a perfectly conducting one-dimensional rough surface. The Dirichlet Green function for the upper half-plane is introduced, in place of the free-space Green function, as the fundamental solution to the Helmholtz equation. Based on this half-plane Green function, two reasonable approximate operations are performed, and an integral equation is formulated to approximate the total field in the two-dimensional space, then to determine the profile of the rough surface as a minimum of the total field. Reconstructions of sinusoidal, non-sinusoidal and random rough surface are performed using numerical techniques. Good agreement of these results demonstrates that the inverse scattering method is reliable.
Characterization of Nonparaxial Truncated Cosine-Gaussian Beams and the Beam Quality in the Far Field
KANG Xiao-Ping, Lü Bai-Da
Chin. Phys. Lett. 2006, 23 (9): 2430-2433 .  
Abstract   PDF(pc) (241KB) ( 479 )
The analytical expression characterizing the propagation of nonparaxial truncated cosine-Gaussian (CoG) beams in free space is derived, and some special cases are discussed. The extended power in the bucket (PIB) is proposed to characterize the beam quality of nonparaxial truncated beams in the far field. It is shown that the extended PIB is applicable to nonparaxial truncated beams, and the PIB of nonparaxial truncated CoG beams depends on the decentred parameter, waist-width-to-wavelength ratio, truncation parameter, and bucket size chosen.

Spontaneous Decay of a Quadrupole between Two Parallel Plates, One or Both Infinitely Permeable
TAN Rong, LI Gao-Xiang
Chin. Phys. Lett. 2006, 23 (9): 2434-2437 .  
Abstract   PDF(pc) (237KB) ( 446 )
We present the explicit expression of the spontaneous decay rate of a quadrupole placed between two parallel plates (one or both the plates have infinite permeability, i.e. μ→∞). It is found that the spontaneous decay rate displays oscillations with the position of the quadrupole, and the oscillations exhibit a symmetric profile with respect to the central plane of the plates for the symmetric models and lack the symmetry for the asymmetric model.
Nonclassical Properties of Superposition of Two Coherent States Shifted in Phase by 3π/2
AHMAD Muhammad Ashfaq, ZENG Ran, LIU Shu-Tian
Chin. Phys. Lett. 2006, 23 (9): 2438-2441 .  
Abstract   PDF(pc) (423KB) ( 427 )
We consider the quantum superposition of two coherent states shifted in phase by 3π/2, |α> and |-iα>, as well as special states that are characterized solely with respect to amplitude α. According to analysis of nonclassical properties such as oscillatory and sub-Poissonian distribution of photon numbers, photon antibunching, quadrature squeezing, and negativity of Wigner function, it is concluded that the considered superposition state is a nonclassical state. Also, the special state is found to exhibit even stronger onclassical features when relative phase Ф of the superposition is equal to the average photon number |α|2.
Modulated Photon Emission of Eu3+ in Microsphere Cavity
YANG Yong, HAN Zheng-Fu, DONG Chun-Hua, XIAO Yun-Feng, GUO Guang-Can
Chin. Phys. Lett. 2006, 23 (9): 2442-2445 .  
Abstract   PDF(pc) (256KB) ( 437 )
Fused silica microsphere with a few Eu3+ ions on the equator is fabricated. The photon emission sharply modulated by whispering gallery (WG) modes is observed under excitation of 395nm laser, which is in agreement with the prediction in theory. The quality factor of the WG modes in microsphere is estimated larger than 3000 from the emission spectrum, which is limited by our monochrometer. It proves that pumping Eu3+ in microsphere cavity in free space is feasible, and this system seems suitable for realizing strong coupling in future quantum computation purposes.
Modulation Frequency Multiplexed Tunable Diode Laser Spectroscopy System for Simultaneous CO, CO2 Measurements
CHEN Dong, LIU Wen-Qing, ZHANG Yu-Jun, LIU Jian-Guo, WEI Qing-Nong, KAN Rui-Feng, WANG Min, CUI Yi-Ben, CHEN Jiu-Ying
Chin. Phys. Lett. 2006, 23 (9): 2446-2449 .  
Abstract   PDF(pc) (259KB) ( 875 )
A modulation frequency multiplexed dual diode-laser system is developed for simultaneous detection of the two most common fire gas products CO and CO2. Simultaneous detection is achieved by modulating each laser at different frequencies, demodulating the signal by a pair of lock-in amplifiers for each gas. Laser beams are combined and detected by one detector after passing through an identical optical path. The experimental results show little performance degradation associated with modulation frequency multiplexing, and no cross-talk between the two multiplexed detection channels is measured.
Cladding-Pumped Tm3+-Doped Large-Mode-Area Fibre Laser Highly Efficient Output at Approximately 2μm
WANG Yue-Zhu, ZHANG Yun-Jun, YAO Bao-Quan, JU You-Lun
Chin. Phys. Lett. 2006, 23 (9): 2450-2451 .  
Abstract   PDF(pc) (182KB) ( 484 )
A cladding-pumped Tm3+-doped fibre laser is carried out to generate continuous-wave output power up to 8.4W at approximately 2μm with a slope efficiency of 57% compared to the launched pump power. When the fibre is cooled by water, the slope efficiency increases greatly and the output laser spectrum has a blue shift.

Experimental Investigation of Tm3+-Doped Silica Double-Cladding Fibre Laser
ZHANG Yun-Jun, WANG Yue-Zhu, JU You-Lun, YAO Bao-Quan
Chin. Phys. Lett. 2006, 23 (9): 2452-2454 .  
Abstract   PDF(pc) (208KB) ( 497 )
Using a Tm3+-doped double-cladding silica fibre, we produce a maximum cw 2.2W output at approximately 2μm. The highest achieved slope efficiency is 29.3% respect to the launched pump power. The lowest threshold is 1.85W using the double pass pump method with the fibre length 2.7m, which is the lowest reported threshold of cladding pump of the 3+H4 level. The fibre laser output peak wavelength ranges from 1.967μm to 2.018μm with cavity 1 (R1=1 and R2=0.04) and from 1.95μm to 1.99μm with cavity 2 (R1=0.04 and R2=0.04), as the fibre length varies.
LD Pump Single-Longitudinal-Mode Nd:GdVO4/RTP Solid-State Green Laser
ZHOU Cheng
Chin. Phys. Lett. 2006, 23 (9): 2455-2457 .  
Abstract   PDF(pc) (191KB) ( 750 )
The single-longitudinal-mode Nd:GdVO4/RTiOPO4 (RTP) solid-state Green laser operation of a laser-diode (LD) end-pumped laser is realized by multi-cavities and a Brewster plate. The LD-pumped single-frequency green laser has been demonstrated by optimizing several parameters and a cavity length, with precise temperature controlling of Nd:GdVO4, RTP and laser diode. When the incident pump power is 2W at 808.4nm, a single-frequency cw green laser at 532nm with output 210mW is obtained, the optical-to-optical conversion efficiency is up to 10.5%.
A Simple Model to Describe the Requirement of Realizing All-Optical Poling
GUO Bin, GUO Fu-Quan, CHEN Yong, ZHU Li-Jun, LIU Fu-Sheng, ZHANG Qi-Jin, WANG Gong-Ming
Chin. Phys. Lett. 2006, 23 (9): 2458-2460 .  
Abstract   PDF(pc) (200KB) ( 355 )
All-optical poling (AOP) of a crosslinkable polymer based on hexamethoxymethyl melamine (HMMM) and Disperse red 1 (DR-1) is investigated. It is found that the saturation second harmonic generation (SHG) intensity decreases significantly with the increase of the sample temperature from 33°C to 63°C. From the perspective of energy equilibrium, the main factors of AOP are analysed, and by introducing the classical ideal gas model, a simple inequation is first deduced to describe the requirement of realizing AOP.

Laser Phase Relations of High-Order Harmonic Generation
GE Yu-Cheng
Chin. Phys. Lett. 2006, 23 (9): 2461-2464 .  
Abstract   PDF(pc) (244KB) ( 550 )
Laser phase relations of high-order harmonic generation (HHG) are calculated with the saddle point theory. The results show a two-peak structure including a symmetric and an asymmetric temporal distributions of the instantaneous frequency of HHG radiation. These distributions are fitted with Gaussian and polynomial functions, respectively. Two calculation formulae are presented to analyse attosecond x-rays with specified time duration and energy bandwidth in experiments.
A Stable Ultrashort Pulse Generator Based on EAM and Well-Designed Compressor for Applications in 160Gbit/s OTDM Networks
YANG Yan-Fu, LOU Cai-Yun, FENG Yan-Ming, WANG Jia-Jun, GAO Yi-Zhi
Chin. Phys. Lett. 2006, 23 (9): 2465-2467 .  
Abstract   PDF(pc) (224KB) ( 586 )
A stable 10GHz ultrashort pulse generator consisted of an electroabsorption modulator (EAM) and a well-designed fibre-based pulse compressor is proposed and demonstrated experimentally. The obtained short pulse has high extinction ratio, no pedestal, low timing jitter, and FWHM of only 2.4ps. The excellent performance of multiplexing from 10GHz to 160GHz confirms the potential of the generator for applications in 160Gbit/s optical time-division-multiplexing (OTDM) systems.
All-Optical Photorefractive Effect in Carbazole-Based Azo-Side Group Polymer
HUANG Mao-Mao, CHEN Zhi-Jian, SHI Jun, CAO Shao-Kui, GONG Qi-Huang
Chin. Phys. Lett. 2006, 23 (9): 2468-2471 .  
Abstract   PDF(pc) (274KB) ( 557 )
We observe the photorefractivity without bias voltage or prepoling in a bifunctional photorefractive polymer. The maximum two-beam coupling gain is measured to be 126cm-1 at zero bias voltage. The sample is considered to be poled by the photoinduced longitudinal electric field, which is formed due to the light intensity gradient along the light path. The expression of the electric field was deduced. The energy transfer direction between two writing beams and light intensity dependence of the two-beam coupling gain coefficient is predicted to be consistent with the experimental results. Furthermore, the dependence of the two-beam coupling gain coefficient on external applied electrical field is measured and this experiment verifies the existence of the photoinduced longitudinal electric field.
Light-Propagation Characteristics of Photonic Crystal Waveguide Based on SOI Materials at Different Polarized States
WANG Chun-Xia, XU Xing-Sheng, LI Fang, DU Wei, XIONG Gui-Guang, LIU Yu-Liang, CHEN Hong-Da
Chin. Phys. Lett. 2006, 23 (9): 2472-2475 .  
Abstract   PDF(pc) (425KB) ( 623 )
Straight single-line defect optical waveguides in photonic crystal slabs are designed by the plane wave expansion method and fabricated into silicon-on-insulator (SOI) wafer by 248-nm deep UV lithography. We present an efficient way to measure the light transmission spectrum of the photonic crystal waveguide (PhC WG) at given polarization states. By employing the Mueller/Stokes method, we measure and analyse the light propagation properties of the PhC WG at different polarized states. It is shown that experimental results are in agreement with the simulation results of the three-dimensional finite-difference-time-domain method.
A Fully Vectorial Effective Index Method for Accurate Dispersion Calculation of Photonic Crystal Fibres
XU Yong-Zhao, REN Xiao-Min, ZHANG Xia, HUANG Yong-Qing
Chin. Phys. Lett. 2006, 23 (9): 2476-2479 .  
Abstract   PDF(pc) (261KB) ( 753 )
A fully vectorial effective index method is developed for accurate dispersion calculation of photonic crystal fibres (PCFs). In order to improve the accuracy of the model, different values for the effective
core radius are used when PCFs have different fibre parameters. The accuracy of our approach is demonstrated by comparing our results with other numerical and experimental results reported in literature. It is found that the accuracy of the fully vectorial effective index method is improved and our results agree well with accurate numerical results obtained by other methods as well as the previously reported experimental data.
Demodulating the Response of Optical Fibre Long-Period Gratings: Genetic Algorithm Approach
P. S. André, R. A. Sá. Ferreira, C. M. L.Correia, H. Kalinowshy, XIN Xiang-Jun, J. L. Pinto,
Chin. Phys. Lett. 2006, 23 (9): 2480-2482 .  
Abstract   PDF(pc) (205KB) ( 379 )
The extraction of the physical parameters of long period gratings from the spectral response is not an easy process. We present a demodulation technique to synthesize the physical parameters of a long period grating recorded in an optical fibre. The demodulation is achieved through the implementation of a genetic algorithm. The extracted parameters are in agreement with the typical values known for long period gratings.
Time-Domain Geoacoustic Inversion Based on Normal Incidence Reflection from Layered Sediment
GUO Yong-Gang, LI Feng-Hua, LIU Jian-Jun, LI Zheng-Lin
Chin. Phys. Lett. 2006, 23 (9): 2483-2486 .  
Abstract   PDF(pc) (240KB) ( 551 )
We present a new geoacoustic inversion approach based on the stable inversion of sediment acoustic impedance from normal incident reflection data. The Hamilton empirical formulae are utilized to separate the impedance into velocity and density. The inverted results are evaluated by the measurement on the core samples. The predicted transmission losses (TLs) using the inverted results are in good agreement with the measured TLs from the explosive sources.
Numerical Simulation of the Non-Fourier Heat Conduction in a Solid-State Laser Medium
TAO Yu-Jia, HUAI Xiu-Lan, LI Zhi-Gang,
Chin. Phys. Lett. 2006, 23 (9): 2487-2490 .  
Abstract   PDF(pc) (240KB) ( 944 )
A hyperbolic model of non-Fourier heat conduction with non-uniform heat source is used to simulate the transient heat transfer in a high-pulse-pumped solid-state laser medium. The temperature fields are numerically analysed using the finite difference method combined with the TDMA algorithm for different pump power densities, pulse durations, thermal relaxation time and cooling intensities, respectively. The calculated results are compared with those predicted by the parabolic heat conduction model based on the Fourier law. The results indicate that the non-Fourier heat conduction phenomenon in laser media should be considered when the pump power density exceeds 104W/m2 or under low pulse duration. In addition, the conditions of non-Fourier effects and their influencing factors are analysed.

Displacement Mechanism of Polymer Flooding by Molecular Tribology
YANG Er-Long, SONG Kao-Ping
Chin. Phys. Lett. 2006, 23 (9): 2491-2493 .  
Abstract   PDF(pc) (200KB) ( 748 )
Whether polymer flooding can enhance displacement efficiency or not is still a problem under debate. Laboratory experiment, numerical simulation and core data analysis are the commonly used means to study polymer flooding displacement efficiency. We discuss the limitations of these methods and employ molecular tribology to study the problem. The black--white ball action principle, i.e. the atom action model for describing the friction principle, is used to analyse the microscopic mechanism of oil displacement and describe the molecular interactions and displacement power during polymer flooding. Both tribology theory and dynamic rheological test show that molecular interactions during polymer flooding are bigger than that during water flooding. It is concluded that displacement efficiency of water flooding may be higher than that of polymer flooding at particular area; while polymer flooding can weaken the heterogeneity significantly, decrease ineffective injection and enhance the total displacement efficiency.
Analysis of Stability for Gas-Kinetic Non-Local Traffic Model
SUN Xi-Ming, DONG Yu-Jie
Chin. Phys. Lett. 2006, 23 (9): 2494-2497 .  
Abstract   PDF(pc) (392KB) ( 455 )
The gas-kinetic non-local traffic model is improved by taking into account the relative velocity of the correlated vehicles. The stability of different relaxation time modes is analytically investigated with the perturbation method. The analysis and numerical simulations validate that the density-velocity dependent relaxation time model is more stable than the other gas-kinetic traffic models in the high density traffic jams.
Ambipolar Diffusion in Direct-Current Positive Column with Variations in Radius of Discharge Tube
Chin. Phys. Lett. 2006, 23 (9): 2498-2501 .  
Abstract   PDF(pc) (257KB) ( 992 )
The ambipolar diffusion and argon ion mobility as functions of the reduced electric field and pressure times the tube radius are investigated in a weakly ionized non-uniform glow discharge plasma system. In particular, the variable cross section at the same discharge tube on the ambipolar diffusion coefficient shows a more noticeable effect than the effects from the ion mobility. As the diffusion length Λ increases, the ambipolar diffusion Da increases. However, it decreases as the discharge current is increased.
Pellet Enhanced Performance on the HL-2A Tokamak
DING Xuan-Tong, YANG Qing-Wei, YAN Long-Wen, ZHU Gen-Liang, XIAO Zheng-Gui, LIU De-Quan, CAO Zeng, GAO Qing-Di, LONG Yong-Xing, LIU Yi, ZHOU Yan, PAN Yu-Dong, CUI Zheng-Ying, HUANG Yuan, LIU Ze-Tian), SHI Zhong-Bing, JI Xiao-Quan, XIAO Wei-Wen, LIU Yong
Chin. Phys. Lett. 2006, 23 (9): 2502-2505 .  
Abstract   PDF(pc) (311KB) ( 468 )
Enhanced confinement has been achieved by the centre fuelling of pellet injection on the HL-2A tokamak. The energy confinement time increases from 50ms to 140ms after the pellet injection. Experimental results show that the improvement of the confinement is related to the decrease of the electron heat transport. everal phenomena which may lead to the improved confinement have been observed in the experiments. After the pellet injection the hollow electron temperature profile and the peaked electron density profile can be sustained for about 200ms, but the improved confinement remains at about 500ms. Sawtooth features and MHD modes have been observed by soft x-ray array and the Mirnov probes. The weak (or reversed) magnetic shear is thought to be an important cause of the low electron heat transport.
Population Diagnostics of a Hot NaBr Plasma by Detailed Simulation of Absorption Spectra
JIN Feng-Tao, ZENG Jiao-Long, YUAN Jian-Min
Chin. Phys. Lett. 2006, 23 (9): 2506-2509 .  
Abstract   PDF(pc) (243KB) ( 400 )
The experimental absorption spectra of a hot NaBr plasma are theoretically studied by using a detailed level accounting model. The sodium and bromine absorption spectra have been well reproduced respectively in the approach of local thermodynamic equilibrium, in which the populations between and within ions are obtained by solving the Saha--Boltzmann equation. The temperature of bromine however is found to be much lower than the one of sodium. Such discrepancy indicates that thermodynamic equilibrium is not reached between the sodium and bromine atoms during the measurement.
Microstructure Study on Heterostructures of AlInGaN/GaN/Al2O3 by Using Rutherford ackscattering/Channelling and XRD
WANG Huan, YAO Shu-De, PAN Yao-Bo, YU Tong-Jun, ZHANG Guo-Yi
Chin. Phys. Lett. 2006, 23 (9): 2510-2512 .  
Abstract   PDF(pc) (228KB) ( 512 )
A quaternary AlInGaN layer is grown by metal--organic chemical vapour deposition on a sapphire (0001) substrate with a thick (>1μm) GaN intermediate layer. The compositions of In and Al are determined by Rutherford backscattering (RBS). The low ratio between the channelling yield and random yield according to the spectra of RBS/C (Xmin=1.44%) means that the crystal quality of the AlInGaN film is perfect. The perpendicular and the parallel elastic strain of the AlInGaN layer, e=-0.15% and e//=0.16%, respectively, are derived using a combination of XRD and RBS/channelling.
Discontinuous Structural Phase Transition Behaviour in Multiple Component Alloy Melts
WANG Yu-Qing, WU Yu-Qin, LIU Jian-Tong, BIAN Xiu-Fang
Chin. Phys. Lett. 2006, 23 (9): 2513-2515 .  
Abstract   PDF(pc) (208KB) ( 409 )
Discontinuous structural phase transition behaviour in seven kinds of liquid multiple component alloys are found by using a torsional oscillation viscometer. There are different phases existing in the system and the number of phases is discussed using the equilibrium thermodynamics phase rule. The phase parameters (η0,ε) and order parameter df in different phase regions are calculated based on the researched results. It is found that the parameters (η0,ε, df) change at the structural transition point. The diameter of the fluid clusters, df, is stable in each phase region, which indicates that the structure is uniform.
Multiple-State Storage Capability of Stacked Chalcogenide Films (Si16Sb33Te51/Si4Sb45Te51/Si39Sb Te50) for Phase Change Memory
LAI Yun-Feng, FENG Jie, QIAO Bao-Wei, HUANG Xiao-Gang, CAI Yan-Fei, LIN Yin-Yin, TANG Ting-Ao, CAI Bing-Chu, CHEN Bomy
Chin. Phys. Lett. 2006, 23 (9): 2516-2518 .  
Abstract   PDF(pc) (239KB) ( 761 )
The multiple-state storage capability of phase change memory (PCM) is confirmed by using stacked chalcogenide films as the storage medium. The current--voltage characteristics and the resistance--current characteristics of the PCM clearly indicate that four states can be stored in this stacked film structure. Qualitative analysis indicates that the multiple-state storage capability of this stacked film structure is due to successive crystallizations in different Si--Sb--Te layers triggered by different amplitude currents.

Final Governing Equation of Plane Elasticity of Icosahedral Quasicrystals and General Solution Based on Stress Potential Function
LI Lian-He, FAN Tian-You
Chin. Phys. Lett. 2006, 23 (9): 2519-2521 .  
Abstract   PDF(pc) (178KB) ( 735 )
The stress potential function theory for plane elasticity of icosahedral quasicrystals is developed. By introducing stress functions, huge numbers of basic equations involving elasticity of icosahedral quasicrystals are reduced to a single partial differential equation of the 12th order. The general solution of the equation is expressed by 6 analytic functions of complex variable z=x+iy.
Acoustic Phonon Thermal Transport through a Nanostructure
LI Wen-Xia, LIU Tian-Yu, LIU Chang-Long
Chin. Phys. Lett. 2006, 23 (9): 2522-2525 .  
Abstract   PDF(pc) (249KB) ( 388 )
Using the scattering matrix method, we investigate the thermal transport in a nanostructure at low temperatures. It is found that phonon transport exhibits some novel and interesting features: resonant transmission, resonant reflection, and small thermal conductance. A comparison between thermal conductances is performed when stress-free and hard-wall boundary conditions are applied for acoustic modes, respectively. The result indicates that the characteristics of the thermal conductance versus temperature for different types of boundary conditions are qualitatively different.
Finite Size Effect for the First-Order Phase Transition of the Three-Dimensional Blume--Capel Model on a Cellular Automaton
N. Seferoglu, A. Ö, zkan, B. Kutlu
Chin. Phys. Lett. 2006, 23 (9): 2526-2529 .  
Abstract   PDF(pc) (260KB) ( 351 )
The first-order phase transition of the three-dimensional Blume--Capel model is investigated using the cooling algorithm which is improved from Creutz Cellular Automaton at D/J=2.9, i.e. a ratio of single-ion anisotropy constant to bilinear interaction energy. We test the efficiency of the algorithm and obtain the finite-size effects at the first-order phase transition point. The transition temperature is estimated using the probability distributions of the order parameter and the energy. The analysis of data at the transition point indicates that the magnetic susceptibility and the specific heat maxima increase with the system value (Ld).
A Kilowatt Diode-Pumped Solid-State Heat-Capacity Double-Slab Laser
GUO Ming-Xiu, LI Jin-Dong, FU Wen-Qiang, SHI Xiang-Chun, HU Qi-Quan, CHEN Wei-Biao
Chin. Phys. Lett. 2006, 23 (9): 2530-2533 .  
Abstract   PDF(pc) (238KB) ( 1631 )
A kilowatt diode-pumped solid state heat capacity laser is fabricated with a double-slab Nd:YAG. Using the theoretical model of heat capacity laser output laser characteristics, the relationships between the output power, temperature and time are obtained. The slab is 59×40×4.5mm3 in size. The average pump power is 11.2kW, the repetition rate is 1kHz, and the duty cycle is 20%. During the running time of 1s, the output energy of the laser has a fluctuation with the maximal output energy at 2.06J, and the maximal output average power is 2.06kW. At the end of the second, the output energy declines to about 50% compared to the beginning. The thermal effects can be improved with one slab cooled by water. The experimental results are consistent with the calculation data.
High Spectral Resolution Mo/Si Multilayers Working at High Order Reflection
WU Wen-Juan, ZHU Jing-Tao, WANG Zhan-Shan, ZHANG Zhong, WANG Feng-Li, WANG Hong-Chang, ZHANG Shu-Min, XU Yao, CHENG Xin-Bin, WANG Bei, LI Cun-Xia, WU Yong-Rong, QIN Shu-Ji, CHEN Ling-Yan, ZHOU Hong-Jun, HUO Tong-Lin
Chin. Phys. Lett. 2006, 23 (9): 2534-2537 .  
Abstract   PDF(pc) (278KB) ( 529 )
The high reflectance orders are used to improve the spectral resolution of Mo/Si multilayers. The multilayers for the first-, second- and third-order reflectance are designed and optimized, respectively. These multilayers are fabricated by using a directed current magnetron sputtering system, and the reflectivity is measured in an extreme ultraviolet range by synchrotron radiation. The experimental results show that the spectral resolution λ/Δλ (λ=14nm) increases from 24.6 for the first order to 66.6 for the third order.
Effects of High Pressure on BC3
ZHOU Jin-Ling, CUI Tian, MA Yan-Ming, LIU Zhi-Ming, LIU Bing-Bing, ZOU Guang-Tian
Chin. Phys. Lett. 2006, 23 (9): 2538-2541 .  
Abstract   PDF(pc) (276KB) ( 623 )
High-pressure phases of BC3 are studied within the local density approximation under the density functional theory framework. When the pressure reaches 20GPa, the layered BC3 that is a semiconductor at ambient pressure, becomes metallic. As the pressure increases, the material changes into a network structure at about 35GPa. To understand the mechanism of phase transitions, band structure and density of states are discussed. With the increase of pressure, the width of bands broadens and the dispersion of bands enlarges. Additionally, the density of states of the network bears great resemblance to that of diamond. Formation of the sp3 bonding in the network is the main reason for the structural transformation at 35GPa.
Energy Spectrum Symmetry of Heisenberg Model in Fock Space
WANG An-Min, ZHU Ren-Gui
Chin. Phys. Lett. 2006, 23 (9): 2542-2544 .  
Abstract   PDF(pc) (199KB) ( 427 )
We extend the BCS paring model with equally spaced energy levels to a general one-dimensional spin-1/2 Heisenberg model. The two well-known symmetries of the Heisenberg model, i.e. permutational and spin-inversion symmetries, no longer exist. However, when jointing these two operations together, we find a new symmetry of energy spectrum between its subspace $n$ and subspace $L-n$ of the Fock space. A rigorous proof is presented.
Pure Reflection and Refraction of a Surface Polariton by a Matched Waveguide Structure
A Zhong-Tuan, WANG Pei, CAO Yong, TANG Hong-Gao, MING Hai
Chin. Phys. Lett. 2006, 23 (9): 2545-2548 .  
Abstract   PDF(pc) (244KB) ( 769 )
We study the fundamental problem of reflection and refraction of a surface polariton as it strikes the interface between two waveguide structures. By making the two waveguide structures match to each other, coupling of surface polaritons to radiating modes is cancelled, and the reflected and transmitted waves consist of only surface modes. The reflection and transmission coefficients are calculated, and negative refraction of surface polaritons is demonstrated. Finite-difference time-domain numerical simulations are also performed to verify the analytical results. As one of the applications of the matched waveguide structure, a square corner reflector for phase-retardation-free reflection of surface polaritons is proposed.

Spin Filter Effect in Organic Polymers in the Presence of Local Magnetic Field
YAN Yong-Hong, CHEN Mei-Juan, WU Chang-Qin
Chin. Phys. Lett. 2006, 23 (9): 2549-2552 .  
Abstract   PDF(pc) (241KB) ( 852 )
Using a nonadiabatic evolution method, we investigate the spin filter effect in organic polymers in the presence of a local magnetic field. Through a spin-dependent magnetic field, polarons (charge carrier) with different spins will feel repulsive or attractive force determined by their spins. Our simulations show that in a single-site magnetic field (affecting electrons at a single site), for example V150=0.35eV, or V150=0.45eV, a spin-up polaron accelerated to saturated velocity by an electric field can pass through the field while the spin-down polaron is trapped. When the local field extends over several sites (Vn ~ exp[-(n-nc) sup>2/n2w]), similar behaviour is also found. Simultaneously we find that it is more likely to realize the spin filter effect in a comparatively large field since the polaron which feels attractive force is easily trapped by a local magnetic field.
Improved Fluorescence from Tm3+/Er3+/Ce3+ Triply Doped Bismuth-Silicate Glasses for S+C-bands Amplifiers
WANG Xun-Si, NIE Qiu-Hua, LIU Li-Ren, XU Tie-Feng, SHEN Xiang, DAI Shi-Xun, ZHANG Xiang-Hua
Chin. Phys. Lett. 2006, 23 (9): 2553-2556 .  
Abstract   PDF(pc) (301KB) ( 1017 )
Fluorescence of Tm3+/Er3+ codoped bismuth-silica (BS) glasses and the sensitization of Ce3+ are investigated. It shows that Ce3+ codoping with Tm3+/Er3+ in BS glasses results in a quenching of Tm3+ ion emission from 3+F4 to the 3+H4 level. Consequently, the 1.47μm emission occurs after the population inversion between the 3+H4 and 3+F4 levels. Furthermore, the codoped glasses show the broad emission spectra over the whole S and C bands with full-width at half-maximum (FWHM) up to about 119nm, as it combines 1.55μm emission band of Er3+ with 1.47μm emission band of Tm3+ under 800nm excitation.
Total Dose Radiation Tolerance of Phase Change Memory Cell with GeSbTe Alloy
WU Liang-Cai, LIU Bo, SONG Zhi-Tang, FENG Gao-Ming, FENG Song-Lin, CHEN Bomy
Chin. Phys. Lett. 2006, 23 (9): 2557-2559 .  
Abstract   PDF(pc) (243KB) ( 539 )
Phase change memory (PCM) cell array is fabricated by a standard complementary metal--oxide--semiconductor process and the subsequent special fabrication technique. A chalcogenide Ge2Sb2Te5 film in thickness 50nm deposited by rf magnetron sputtering is used as storage medium for the PCM cell. Large snap-back effect is observed in current--voltage characteristics, indicating the phase transition from an amorphous state (higher resistance state) to the crystalline state (lower resistance state). The resistance of amorphous state is two orders of magnitude larger than that of the crystalline state from the resistance measurement, and the threshold current needed for phase transition of our fabricated PCM cell array is very low (only several μA). An x-ray total dose radiation test is carried out on the PCM cell array and the results show that this kind of PCM cell has excellent total dose radiation tolerance with total dose up to 2×106rad(Si), which makes it attractive for space-based applications.
Break Cohesion of Metal Contacts due to Voltage Bias
LI Yu-Xian
Chin. Phys. Lett. 2006, 23 (9): 2560-2562 .  
Abstract   PDF(pc) (203KB) ( 431 )
The instability of metal point contacts under voltage bias is calculated based on scattering theory. When the bias is applied, the transport channels will be closed and the chemical bonds will be broken, which modify the cohesive force of the point contact. If the cross section of the contact is narrow enough, an applied bias will break the point contact, which is in agreement with the experimental results. The effect of bias-dependent force can play an important role in the stability of a nanosize device.

Geometric and Electronic Properties of Highly Fluorinated Fullerene C74F38
WU Hai-Ping, LU Gong-Li, YUAN Yong-Bo, DENG Kai-Ming, LIU Yu-Zhen, YANG Jin-Long
Chin. Phys. Lett. 2006, 23 (9): 2563-2565 .  
Abstract   PDF(pc) (233KB) ( 422 )
Geometric and electronic properties of highly fluorinated fullerene C74F38 have been studied using the density functional theory at BLYP level with the double numerical atomic orbital basis sets with polarization functions (DNP). The optimized geometry of C74F38, quite different from that of C74, turns into a pronounced hexahedron shape because the six stabilizing isolated benzenoid rings tend to be as far apart as possible. The HOMO--LUMO energy gap and the binding energy of C74F38 indicate that C74F38 is not only kinetically but also dynamically stable. The shorter F--C bond lengths together with the analysis of the density of states and the Mulliken populations indicate that the F--C bonds in C74F38 have both covalent and ionic characters. The Mulliken populations show that the fluorine atoms obtain about 10 electrons from the C74cage.
Effect of Nonradiative Recombination on Carrier Dynamics in GaInNAs/GaAs Quantum Wells
SUN Zheng, WANG Bao-Rui, XU Zhong-Ying, SUN Bao-Quan, JI Yang, NI Hai-Qiao, NIU Zhi-Chuan
Chin. Phys. Lett. 2006, 23 (9): 2566-2569 .  
Abstract   PDF(pc) (301KB) ( 560 )
The nonradiative recombination effect on carrier dynamics in GaInNAs/GaAs quantum wells is studied by time-resolved photoluminescence (TRPL) and polarization-dependent TRPL at various excitation intensities. It is found that both recombination dynamics and spin relaxation dynamics strongly depend on the excitation ntensity. Under moderate excitation intensities the PL decay curves exhibit unusual non-exponential behaviour. This result is well simulated by a rate equation involving both the radiative and non-radiative recombinations via the introduction of a new parameter of the effective concentration of nonradiative recombination centres in the rate equation. In the spin dynamics study, the spin relaxation also shows strong excitation power dependence. Under the high excitation power an increase of spin polarization degree with time is observed. This new finding provides a useful hint that the spin process can be controlled by excitation power in GaInNAs systems.
Influence of Self-Absorption and Impurities on Scintillation Properties of (Lu0.1Y0.9)AlO3:Ce Single Crystals
DING Dong-Zhou, LU Sheng, QIN Lai-Shun, REN Guo-Hao
Chin. Phys. Lett. 2006, 23 (9): 2570-2572 .  
Abstract   PDF(pc) (245KB) ( 460 )
Lu0.1Y0.9AlO3:Ce single crystals in dimensions ∅30×90mm3 are successfully grown by the Czochralski method. The light output and energy resolution of the crystal in dimensions ∅14×2mm3 are 9420 photons/MeV and 12.5% respectively. Dependence of the light output on the thickness of the sample is found and explained by the self-absorption in the range of 320--370nm and the underlying parasitic absorption around 250nm. In addition, the local enrichment of Ce ions and the presence of low-valent impurity ions may cause the deterioration of its light output. In addition, Lu0.1Y0.9AlO3:Ce has an almost constant fluorescence decay time of 16ns in the temperature range of 80--373K.

New BCN Fibres for Strong Ultraviolet and Visible Light Luminescence
YANG Jian, QIU Tai, SHEN Chun-Ying
Chin. Phys. Lett. 2006, 23 (9): 2573-2575 .  
Abstract   PDF(pc) (225KB) ( 513 )
Novel B3CN3 fibres with a special structure have been synthesized by a pyrolysis process. High-resolution TEM analysis shows that the as-prepared B3CN3 fibres can be described as a nanofibre-interweaved network. Strong photoluminescence at 370nm and 700nm from the as-prepared B3CN3 fibres are observed at room temperature, which suggests that B3CN3 is a promising ultraviolet- and visible-light-emitting material.
Effect of Alumina and Chromium Interlayers on Microstructures and Optical Properties of Thin Ag Films on Glass Substrates
SUN Xi-Lian, SHAO Jian-Da
Chin. Phys. Lett. 2006, 23 (9): 2576-2578 .  
Abstract   PDF(pc) (241KB) ( 1047 )
Effects of alumina and chromium interlayers on the microstructure and optical properties of thin Ag films are investigated by using spectrophotometry, x-ray diffraction and AFM. The characteristics of Ag films in Ag/glass, Ag/Al2O3/glass and Ag/Cr/glass stacks are analysed. The results indicate that the insertion of an Al2O3 or Cr layer decreases the grains and influences the reflectance of Ag films. The reflectance of the Ag film can be increased by controlling the thickness of alumina interlayer. The stability of Ag films is improved and the adhesion of Ag films on glass substrates is enhanced by alumina as an interlayer.
Enhancement of Photoluminescence Intensity of GaInNAs/GaAs Quantum Wells by Two-Step Rapid Thermal Annealing
ZHAO Huan, XU Ying-Qiang, NI Hai-Qiao, HAN Qin, WU Rong-Han, NIU Zhi-Chuan
Chin. Phys. Lett. 2006, 23 (9): 2579-2582 .  
Abstract   PDF(pc) (243KB) ( 560 )
We investigate the effect of rapid thermal annealing on InGaNAs/GaAs quantum wells. At optimized annealing temperatures and times, the greatest enhancement of the photoluminescence intensity is obtained by a special two-step annealing process. To identify the mechanism affecting the material quality during the rapid thermal annealing, differential temperature analysis is applied, and temperature- and power-dependent photoluminescence is carried out on the samples annealed under different conditions. Our experiment reveals that some composition redistribution or other related ordering processes may occur in the quantum-well layer during annealing. Annealing at a lower temperature for a long time primarily can remove defects and dislocations while annealing at a higher temperature for a short time primarily homogenizes the composition in the quantum wells.
Influence of GaAsP Insertion Layers on Performance of InGaAsP/InGaP/AlGaAs Quantum-Well Laser
CAO Yu-Lian, LIAN Peng, MA Wen-Quan, WANG Qing, WU Xu-Ming, HE Guo- Rong, LI Hui, WANG Xiao-Dong, SONG Guo-Feng, CHEN Liang-Hui
Chin. Phys. Lett. 2006, 23 (9): 2586-2586 .  
Abstract   PDF(pc) (250KB) ( 513 )
We report on the use of very thin GaAsP insertion layers to improve the performance of an GaAsP/InGaP/AlGaAs single quantum-well laser structure grown by metal organic chemical vapour deposition. Compared to the non-insertion structure, the full width at half maximum of photoluminescence spectrum of the insertion structure measured at room temperature is decreased from 47 to 38nm indicating sharper interfaces. X-ray diffraction shows that the GaAsP insertion layers between AlGaAs and InGaP compensates for the compressive strain to improve the total interface. The laser performance of the insertion structure is significantly improved as compared with the counterpart without the insertion layers. The threshold current is decreased from 560 to 450mA while the slope efficiency is increased from 0.61 to 0.7W/A and the output power is increased from 370 to 940mW. The slope efficiency improved is very high for the devices without coated facets. The improved laser performance is attributed to the suppression of indium carry-over due to the use of the GaAsP insertion layers.
Experimental Investigation of an L-Shaped Very-Small-Aperture Laser
XU Ji-Ying, WANG Jia, GAI Hong-Feng, TIAN Qian, WANG Bo-Xiong, HAO Zhi-Biao, HAN Shuo
Chin. Phys. Lett. 2006, 23 (9): 2587-2590 .  
Abstract   PDF(pc) (273KB) ( 542 )
An L-shaped very-small-aperture laser (VSAL) with high power output and field enhancement effect is fabricated and characterized. As a comparison, a conventional rectangular VSAL and a double-aperture VSAL containing one L-aperture and one rectangular aperture are also fabricated and measured. The confined optical fields in the vicinity of apertures of VSAL are detected using an apertured near-field scanning optical microscope. The experimental results reveal that the power output from the L-shaped VSAL increases about 13 times than the rectangular VSAL with a comparable aperture area. It is indicated that the L-shaped VSAL has strong power output enhancement effect. The near-field distribution of the double-aperture VSAL indicates that the L-aperture has the field confinement and enhancement effect stronger than the rectangular aperture.

Reduction of Dislocations in GaN Epilayer Grown on Si (111) Substrates using a GaN Intermedial Layer
WANG Jian-Feng, ZHANG Bao-Shun, ZHANG Ji-Cai, ZHU Jian-Jun, WANG Yu-Tian, CHEN Jun, LIU Wei, JIANG De-Sheng, YAO Duan-Zheng, YANG Hui
Chin. Phys. Lett. 2006, 23 (9): 2591-2594 .  
Abstract   PDF(pc) (271KB) ( 1035 )
GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AlN/Si(111) substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional (3D) mode to the 2D one occurs during the GaN epilayer growth when a higher growth pressure is used during the preceding GaN intermedial layer growth, and an improvement of the crystalline quality of GaN epilayer will be made. Combining the in situ reflectivity and transmission electron microscopy (TEM) measurements, it is suggested that the lateral growth at the transition of growth mode is favourable for bending of dislocation lines, thus reducing the density of threading dislocations in the epilayer.
Influence of Positive Bias on Electrical Properties of Undoped Nanocrystalline Diamond Films
WU Nan-Chun, XIA Yi-Ben, TAN Shou-Hong, WANG Lin-Jun, LIU Jian-Min, SU Qing-Feng
Chin. Phys. Lett. 2006, 23 (9): 2595-2597 .  
Abstract   PDF(pc) (210KB) ( 517 )
By means of electron assisted hot filament chemical vapour deposition technology, nanocrystalline diamond films are deposited on polished n-(100)Si wafer surface at 1kPa gas pressure. The deposited films are characterized with a Raman spectrometer, atomic force microscope, semiconductor characterization system and Hall effect measurement system. The results show that, when bias current is larger than 2A, sheet hole concentration can increase to a value greater than 1013cm-2 and undoped nanocrystalline diamond films with a p-type semiconducting characteristic form. Heterojunction between n-Si substrate and the nanocrystalline diamond films deposited with 2A and 6A bias current has an evident junction effect. Hole formation mechanisms in the films are discussed.
Effect of Photo-Oxidation on Energy Transfer in Light Harvesting Complex (LH2) from Rhodobacter Sphaeroides 601
LIU Kang-Jun, LIU Wei-Min, YAN Yong-Li, DONG Zhi-Wei, LIU Yuan, XU Chun-He, QIAN Shi-Xiong
Chin. Phys. Lett. 2006, 23 (9): 2598-2601 .  
Abstract   PDF(pc) (273KB) ( 453 )
We study the photo-oxidation of bacteriochlorophylls (BChls) in peripheral light harvesting complexes (LH2) from rhodobacter sphaeroides by using the steady absorption and the femtosecond pump--probe measurement, to realize the detailed dynamics of LH2 in the presence of photo-oxidation. The experimental results reveal that BChl-B850 radical cations may act as an additional channel to compete with the unoxidized BChl-B850 molecules for rapidly releasing the excitation energy, while the B800→B850 energy transfer rate is almost unaffected in the oxidation process.
Water Gas Shift Reaction: A Monte Carlo Simulation
Chin. Phys. Lett. 2006, 23 (9): 2602-2605 .  
Abstract   PDF(pc) (221KB) ( 591 )
The water gas shift (WGS) reaction is a process of industrial importance. In this reaction carbon monoxide reacts with water on a catalytic surface to form CO2 and H2. We study this reaction with thermal (Langmuir--Hinshelwood) and non-thermal (precursor and Eley--Rideal) reaction mechanisms using the techniques of Monte Carlo computer simulation. The details of surface coverages and production rates are given as a function of CO partial pressure. The diffusion of species on the surface as well as their desorption from the surface is also introduced to include temperature effects. The phase diagrams of the system have been drawn to observe the behaviour of reacting species on the surface. The study reveals that the production rates are higher for non-thermal precursor mechanism and are in agreement with the experimental finding.
Recombination Reduction in Dye-Sensitized Solar Cells by Screen-Printed TiO2 Underlayers
LIU Xi-Zhe, HUANG Zhen, LI Ke-Xin, LI Hong, LI Dong-Mei, CHEN Li-Quan, MENG Qing-Bo
Chin. Phys. Lett. 2006, 23 (9): 2606-2608 .  
Abstract   PDF(pc) (229KB) ( 1629 )
In dye-sensitized solar cells (DSSCs), the TiO2 underlayer can block the electron recombination at the FTO (fluorine doped SnO2) glass/electrolyte interface. This underlayer was traditionally prepared by spray-pyrolysis or spin coating. In this study, we develop an alternative method based on screen-printing. The quality of the screen-printed underlayers is characterized by SEM, XPS and the hotoelectrochemistry measurements. The prepared underlayers are smooth and effective. The screen-printing technique is cheap and easy to handle and can produce films with different patterns. These advantages will facilitate applications of the screen-printed underlayer.
Effects of Relative Orientation of Molecules on Electron Transport in Molecular Devices
ZHOU Yan-Hong, ZHENG Xiao-Hong, XU Ying, ZENG Zhao-Yang, ZENG Zhi
Chin. Phys. Lett. 2006, 23 (9): 2609-2612 .  
Abstract   PDF(pc) (262KB) ( 579 )
Effects of relative orientation of the molecules on electron transport in molecular devices are studied by the non-equilibrium Green function method based on density functional theory. In particular, two molecular devices with planar Au7 and Ag3 clusters sandwiched between the Al(100) electrodes are studied. In each device, two typical configurations with the clusters parallel and vertical to the electrodes are considered. It is found that the relative orientation affects the transport properties of these two devices completely differently. In the Al(100)--Au7--Al(100) device, the conductance and the current of the parallel configuration are much larger than those in the vertical configuration, while in the Al(100)--Ag3--Al(100) device, an opposite conclusion is obtained.

Effects of Spatial Variation of Thermal Electrons on Whistler-Mode Waves in Magnetosphere
CHEN Lun-Jin, ZHENG Hui-Nan, XIAO Fu-Liang, WANG Shui
Chin. Phys. Lett. 2006, 23 (9): 2613-2616 .  
Abstract   PDF(pc) (263KB) ( 472 )
A ray-tracing method is developed to evaluate the wave growth/damping and specifically propagation trajectories of the magnetospherically reflected Whistler-mode waves. The methodology is valid for weak wave growth/damping when plasma is comprised of a cold electron population and a hot electron population, together with background neutralizing ions, e.g. protons. The effect of anisotropic thermal electrons on the propagation of Whistler-mode waves is studied in detail. Numerical results are obtained for a realistic spatial variation model of plasma population, including the cold electron density distribution, and the thermal electron density and temperature distribution. It is found that, analogous to the case of the typical cold plasma approximation, the overall ray path of Whistler-mode waves is insensitive to the thermal electron density and temperature anisotropy, and the ray path reflects where wave frequency is below or comparable to the local lower hybrid resonance frequency flhr. However, the wave growth is expected to be influenced by the thermal electron population. The results present a first detailed verification for the validity of the typical cold plasma approximation for the propagation of Whistler-mode waves and may account for the observation that the Whistler-mode waves tend to propagate on a particular magnetic shell L where the wave frequency is comparable to flhr.

Plasma Resources of Jupiter’s Main Auroral Oval
XIAO Yong-Deng, CHEN Chu-Xin
Chin. Phys. Lett. 2006, 23 (9): 2617-2620 .  
Abstract   PDF(pc) (240KB) ( 800 )
Jupiter’s aurora exhibits three distinct regions: the satellite footprint emissions, the main oval emissions and all polar emissions. As the case of the Earth, the auroral morphology contains both qualitative and quantitative clues about magnetospheric structure and dynamics. We map along the magnetic field lines to the equatorial plane to track the plasma resources of the main oval in an equilibrium model of Jupiter's magnetosphere. The footprints of the satellites are good references to help us to check the mapping. We find out that the plasma of oval emissions originates from the equatorial plane with a distance of ~ 22.0RJ, which is closer to the Jupiter than 30RJ given by the VIP4 model. However the difference does not deny the conclusion that the upward Birkeland currents produce the oval emissions.

Dark Energy: Relating the Evolutions of the Universe from the Past to the Future
HUANG Zhuo-Yi, WANG Bin, CAI Rong-Gen, SU Ru-Keng,
Chin. Phys. Lett. 2006, 23 (9): 2621-2624 .  
Abstract   PDF(pc) (249KB) ( 889 )
Using the evolution history of the universe, one can make constraint on the parameter space of dynamic dark energy models. We discuss two different parameterized dark energy models. Our results further restrict the combined constraints obtained from supernova and the first-year Wilkinson-microwave-anisotropy-probe observations. From the allowed parameter space, it is found that our universe will experience an eternal acceleration. We also estimate the bound on the physically relevant regions both in the re-inflationary and inflationary phases.

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