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Volume 13 Issue 2
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Original Articles
Riddled Basin of Laser Cooled-Ions in a Paul Trap
SHEN Jing-ling, YIN Hua-wei, DAI Jian-hua, ZHANG Hong-jun
Chin. Phys. Lett. 1996, 13 (2): 81-84 .  
Abstract   PDF(pc) (208KB) ( 473 )
Recently it has been found that the entire basin of a given attractor is riddled with “holes” leading to another attractor. Here we present the first physical system the laser cooled ions in a Paul trap that exhibits riddled basins in frequency-locking attractor.
Regularities for the Non-yrast Bands of the Even-Even Nuclei
ZHAO Yu-min*, XING Xiang-jun, QING Di, CHEN Yan
Chin. Phys. Lett. 1996, 13 (2): 85-88 .  
Abstract   PDF(pc) (182KB) ( 454 )
By the enlightment of the anharmonic vibrator description for the yrast bands of the even-even 38 ≤Z ≤82 nuclei with 2.05 ≤ R (= E4+1 / E2+1) ≤3.15, a similar regularity for the non-yrast bands is revealed. This systematics suggests that the excitations of the non-yrast bands may be regarded as the multi-phonon excitations above the corresponding bandhead, or the intrinsic states.

Effective Masses of Mesons and Nucleon in Hot Medium for the Walecka Model
GAO Song, ZHANG Yi-jun SU Ru-keng
Chin. Phys. Lett. 1996, 13 (2): 89-92 .  
Abstract   PDF(pc) (183KB) ( 472 )
Based on the thermo-field dynamics, the temperature and density dependencies of the effective masses of σ, ω mesons and nucleon in the walecka model have been calculated. The vacuum fluctuation effect is examined. It is found that the vacuum fluctuation is very important and leads to a reduction of ω-meson mass and an enhancement of σ-meson mass in hot and dense medium.
Mutual Neutralization of Na+/O- Ions in Slow Collisions
ZHOU Xiao-xin, DONG Chen-zhong
Chin. Phys. Lett. 1996, 13 (2): 93-96 .  
Abstract   PDF(pc) (181KB) ( 443 )
The mutual neutralization cross sections of Na+/O- ions at low energy have been calculated by using the multichannel Landau-Zener theory. An asymptotic method is used for estimating the coupling matrix elements between the ionic and covalent states at the crossing points of diabatic potential curves. The results of calculation are compared with available experimental data.
On the Symmetric Structure of the Field and Atomic Squeezing in the Jaynes- Cummings Model
XIE Rui-hua, XU Gong-ou, LIU Dun-huan*
Chin. Phys. Lett. 1996, 13 (2): 97-100 .  
Abstract   PDF(pc) (224KB) ( 386 )
A symmetric structure of the field and atomic squeezing (SSFAS) have been exposed in the resonant Jaynes-Cummings model when it is restricted to the following initial condition: the atom in its ground state and the field in the superposition of zero and one-photon number states. The SSFAS is destroyed due to the non-resonant interaction or the interference between the real-photon processes and virtual-photon processes.
Photorefractive Spatial Dark-Soliton Stripes in LiNbO3: Fe Crystal and Their Application
ZHANG Guo-quan, LIU Si-min, XU Jing-jun, ZHANG Guang-yin, SUN Qian
Chin. Phys. Lett. 1996, 13 (2): 101-104 .  
Abstract   PDF(pc) (226KB) ( 522 )
We observed the photorefractive spatial dark-soliton stripes in LiNbO3:Fe crystal, and demonstrate the planar waveguide property of refractive index profile induced by these spatial dark-soliton stripes. We suggest a new mothed to form the planar waveguide utilizing the grating fixing technique.
Measurement of Three Parameters of a Photorefractive Crystal Ce:KNSBN in Codirectional Two-Wave Mixing
LIU Jin-song, LIANG Chang-hong, AN Yu-ying, JI Xuan-mang*, ZHANG Chang-ming
Chin. Phys. Lett. 1996, 13 (2): 105-108 .  
Abstract   PDF(pc) (208KB) ( 439 )
We present a method of measuring the parameters of a photorefractive crystal in codirectional two-wave mixing that is suitable for two-wave mixing in the intermediate stage (before saturation). Three parameters of a crystal. the exponential gain coefficient, saturation intensity and intensity absorption coefficient. can be measured simultaneously by using this method. The three parameters of a Ce:KNSBN are measured and the measured data are checked by another independent measurement.

A New Type of Bistable Switching in Two-Dimensional Nonlinear Optical Superlattices
WANG Zhen-lin. YANG Zhen-ju. MIN Nai-ben
Chin. Phys. Lett. 1996, 13 (2): 109-112 .  
Abstract   PDF(pc) (152KB) ( 504 )
We investigate theoretically optical response in a two-dilnensional optical superlattice with Kerr-type nonlinearity. We find that in addition to the bistability reported in Phys. Rev. Lett. 71 (1993) 1003 by Xu et al., a new type of bistable switching behavior exists. This bistability is based on the occurrence of the stop gap in the linear spectra and the nonlinear mechanism on it, which makes switching between transmitting and non-transmitting states achievable.
Kerr-Lens Effect and Mode Locking in Ring Cavity Ti:Sapphire Laser
ZHANG Gui-zhong, MIAO Lin-shi, XIANG Wang-hua
Chin. Phys. Lett. 1996, 13 (2): 113-116 .  
Abstract   PDF(pc) (223KB) ( 695 )
This paper presents the results of our numerical simulation, made by employing Split-step Fourier Method, of pulsewidth dependence on the physical quantities in ring cavity Ti:sapphire laser. It is revealed through the computed results that Kerr-lens effect which is now qiiantitatively considered plays a dominant role in forming ultrashort pulses and its interaction with dispersion finally determines the duration of
the pulse, which sheds light on further theoretical investigation of the mode locking mechanism. Meanwhile, tile self-consistent results also provide a guideline for the experimental alignment of the laser.

Model of Collisional Sheath in Spherical and Cylindrical Geometries for Plasma Source Ion Implantation
WANG De-zhen, YU Jiong, GONG Ye
Chin. Phys. Lett. 1996, 13 (2): 117-120 .  
Abstract   PDF(pc) (171KB) ( 739 )
A model is developed that describes the temporal evolution of the sheath during a pulse of high negative voltage applied to a spherical and cylindrical target in a plasma such as that present in plasma source ion implantation for the case in which the pressure of the neutral gas is large 4nough that the ion motion in the sheath can be assumed to he highly collisional. The analytic expressions of the sheath expanding ve1ocity are obtained. The positions of the sheath edge as a function of time predicted by the model are in agreement with those obtained by fluid equations.

Two -Dimensional Animal-Like Fractals in Thin Films
GAO Hong-jun, XUE Zeng-quan, WU Quan-de, PANG Shi-jin
Chin. Phys. Lett. 1996, 13 (2): 121-124 .  
Abstract   PDF(pc) (230KB) ( 546 )
We present a few unique animal-like fractal patterns in ionized-cluster-beam deposited fullerene tetracyanoquinodimethane thin films. The fractal patterns consisting of animal-like aggregates such as “fishes” and “quasi-seahorses” have been characterized by transmission electron microscopy. The results indicate that the small aggregates of the animal-like body are composed of many single crystals whose crystalline directions are generally different. The formation of the fractal patterns can be attributed to the cluster-diffusion-limited aggregation.

Coefficient of Thermal Expansion of Liquid Helium II
Pao LU
Chin. Phys. Lett. 1996, 13 (2): 125-128 .  
Abstract   PDF(pc) (127KB) ( 688 )
We can write the coefficient of thermal expansion of liquid helium in terms of the isothermal compressibility. Together they are connected by some terms which are microscopic or quantum mechanical in nature. Here we give the necessary derivation.
Negative Magnetoresistance Effect in La-Pb-Mn-O Bulk Manganese Oxides
ZHAO Tong-yun, LI Min, ZHAO Xue-gen, WANG Fang-wei, LI Yun-fei, SHEN Bao-gen, ZHAO Jian-gao
Chin. Phys. Lett. 1996, 13 (2): 129-132 .  
Abstract   PDF(pc) (208KB) ( 515 )
The structure. magnetic and magnetotransport properties of La1-xPbxMnO bulk manganese oxides prepared by the standard ceramic techniques were investigated by XRD. VSM, ESM and MR measurements. The sintering condition and the hole doped concentration x have a strong influence on the magnetic properties and magnetoresistance effect. The maximum MR, 20% at room temperature under a field of 2T, was obtained for x= 0.4 and the sintered temperature Ts = 1260°C. The correlation among the structure, magnetic and MR is discussed.
Distinguish Different Factors Dominating Superconductivity in Y-Doped Bi2Sr2CaCu2Oy
ZHANG Han, WU Ke, FENG Qing-rong, ZHU Xing, FENG Sun-qi, GAN Zi-zhao
Chin. Phys. Lett. 1996, 13 (2): 133-136 .  
Abstract   PDF(pc) (231KB) ( 536 )
We observed in Y-doped Bi2Sr2CaCu2Oy superconductors an interesting phenomenon, the Tc(onset) of the Y-doped samples is higher, but the Tc (end) is lower than that of Y-free samples. After annealing in N2 atmosphere, the Tc (end) is increased, but the Tc (onset) is hardly changed. After careful studying, by structure analysis, x-ray photoelectron spectroscopy, R - T relationship measurement, and Hall effect, we successfully distinguish the different factors that dominate the superconductivity. of which one is carrier concentration, others may possibly be structure change and charges redistribution.

Anomalies of Doped-LiNbO3 Crystal in Photorefractive Phase Conjugation with Relation to Structural Phase Transformation
LIU J in-song, LIANG Chang-hong, AN Yu-ying, LI Ming-hua, XU Yu-heng, WU Zhong-kang
Chin. Phys. Lett. 1996, 13 (2): 137-140 .  
Abstract   PDF(pc) (193KB) ( 448 )
We investigate the photorefractive phase conjugation in a Ce:Fe:LiNbO3 crystal as a function of temperature (293-393 K) and find the phase conjugate reflectivity increases sharply in the vicinity of 55, 70 and 110°C. The anomalous phenomenon is possibly concerned with the structural phase transformation of a crystal, which induces an extra internal electric field to influence the phase conjugation. The value of the field is estimated at the order of 105 V/m, in agreement with the published data.
Ultrafast Exciton Trapping Dynamics in ZnSe/(CdSe)m (ZnSe))n Short Period Superlattice Quantum Wells
LIN Wei-zhu, PENG Wen-ji, XIE Cang, XU Geng, PENG Zhong-ling, YUAN Shi-xin
Chin. Phys. Lett. 1996, 13 (2): 141-144 .  
Abstract   PDF(pc) (196KB) ( 432 )
The ultrafast exciton trapping dynamics in ZnSe/ZnCdSe short period superlattice quantum wells has been studied by using transient photoluminescence spectroscopy. A rapid exciton trapping time of less than 7ps from the barriers to the wells is measured. In Te doped samples self-trapped excitons give rise to Stokes shifted broad band luminescence and exhibit much longer lifetime.
Green/Blue Photoluminescence from Nanocrystalline Si Thin Films by Rapid Thermal Processing
ZHU Mei-fang, SUN Jing-lan, LIU Shi-xiang, CHEN Gao, CHEN Pei-yi, TANG Yong
Chin. Phys. Lett. 1996, 13 (2): 145-148 .  
Abstract   PDF(pc) (244KB) ( 539 )
The green/blue photoluminescence with peaks centered around 2.4 eV at room temperature was observed from nanocrystalline Si thin films prepared by the three-step rapid thermal annealing of hydrogenated amorphous silicon films. The effect of the parameters of rapid thermal annealing on the light emission was studied. A comparison of photoluminescence feature between the films from the rapid thermal annealing and the furnace annealing of a-Si:H has been carried out.
Polarized Infrared Spectra of Intersubband Transitions in GaAs/AlGaAs Step Multiquantum Wells
CUI Da-fu, YUAN Zhen-yu, CHEN Zheng-hao, MA Jian-wei, ZHOU Yue-liang, LÜ, Hui-bin, HE Meng, YANG Gno-zhen, ZHANG Shu-de*
Chin. Phys. Lett. 1996, 13 (2): 149-152 .  
Abstract   PDF(pc) (231KB) ( 549 )
The polarization dependence of conduction intersubband transitions in GaAs/AIGaAs step multiquantum well structures has been studied using infrared spectroscopy. For S-polarized 45°oblique angle incidence configuration with respect to sample surface normal, the transverse electric (TE) active intersubband transitions were observed. Both transverse electric and transverse magnetic (TM) active intersubband transitions were obtained in P-polarized incidence at 45°angle on sample, which shows a small energy splitting between TE and TM absorption peaks.

Photoreflectance Study of GaN Films on Sapphire Substrate
QIN Lin-hong, YANG Kai, ZHENG You-dou, ZHANG Rong, DAI Xing-jiang, FENG Duan, HUANG Zhen-chun, J. C. Chen
Chin. Phys. Lett. 1996, 13 (2): 153-156 .  
Abstract   PDF(pc) (175KB) ( 538 )
Photoreflectance was used to study the optical properties of single crystal hexagonal GaN films on (0001) sapphire substrate grown by metalorganic chemical vapor deposition. The energy gap of GaN was determined as 3.400eV and the possible origin of the signal was discussed. Optical absorption and reflection were measured. The optical absorption edge of 3.38 eV, and the reflectivity peak at 3.3 eV confirmed the results of photoreflectance.
Molecular Entanglement Analysis Based on the Damping Behavior of Polycarbonate / Epoxy Resin Semi-Interpenetrating Polymer Network
RONG Min-zhi, ZENG Han-min
Chin. Phys. Lett. 1996, 13 (2): 157-160 .  
Abstract   PDF(pc) (241KB) ( 529 )
The characteristics of entanglement structure in polycarbonate/epoxy semiinterpenetrating polymer network at molecular level have been investigated by dynamic mechanical spectrum. It is found that the relaxation of entanglement chains is a kind of synergetic relaxation, which will induce additive internal friction and decrease the apparent activation energy and Tg. The loss areas can represent the degree of interpenetration between the different segments at molecular level.
20 articles