Chin. Phys. B
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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--2000, Vol.9, No.11
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GENERAL

EFFECTS OF NON-CONSERVATIVE FORCES ON LIE SYMMETRIES AND CONSERVED QUANTITIES OF A LAGRANGE SYSTEM

Zhang Rui-chao, Chen Xiang-wei, Mei Feng-xiang
Chin. Phys., 2000, 9 (11): 801-804 doi: 10.1088/1009-1963/9/11/001
Full Text: [PDF 171 KB] (Downloads:511)
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Non-conservative forces are exerted on a Lagrange system. Their effects on Lie symmetries, structure equation and conserved quantities of the system are studied. It can be seen that some Lie symmetries disappear and some new Lie symmetries emerge. Under certain conditions, some Lie symmetries will still remain present.
CLASSICAL AREAS OF PHENOMENOLOGY

THEORY OF INTERBAND COHERENCE AND INVERSIONLESS BISTABILITY IN SEMICONDUCTOR LASERS

Ge Guo-qin, Leung Pui Tang
Chin. Phys., 2000, 9 (11): 813-823 doi: 10.1088/1009-1963/9/11/004
Full Text: [PDF 310 KB] (Downloads:376)
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Coherent transitions of charge carriers between the conduction and valence bands of a semiconductor medium are essential for the operation of a semiconductor laser. In this paper, we study how such interband coherence can be set up by an injection current and a coherent pump-field. In the absence of the pump-field, the injection current is the only source to establish the interband coherence in a semiconductor laser system. A laser threshold is obtained, which shows that a strongly coupled high-Q microcavity has a low threshold value. However, when an external pump-field serving as another mechanism to create the interband coherence is applied, the threshold value of the injection current can be lowered and it vanishes for sufficiently strong field. Besides, if the pump-field exceeds a threshold value, it is even possible to achieve a bistability in the inversionless region. Some fundamental macroscopic properties, including polarization, absorption and dispersion for the semicoductor system, are also obtained analytically.

EFFECT OF SPHERICAL ABERRATION INTRODUCED BY WATER SOLUTION ON TRAPPING FORCE

Yao Xin-cheng, Li Zhao-lin, Guo Hong-lian, Cheng Bing-ying, Han Xue-hai, Zhang Dao-zhong
Chin. Phys., 2000, 9 (11): 824-826 doi: 10.1088/1009-1963/9/11/005
Full Text: [PDF 210 KB] (Downloads:462)
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Trapping force of an optical tweezers system with an oil immersion objective is calculated with a ray-optics model. Results indicate that the trapping force will be decreased as a result of the introduction of spherical aberration, which is caused by the refractive mismatch between objective oil and water, when the sample manipulated is suspended in a water solution. The effect of spherical aberration will be serious when the detection depth of the optical tweezers is enhanced.

LASING FROM A DYE-DOPED PENDANT DROP AND ITS PRECESSION

Pu Xiao-yun, Lee Wing-Kee
Chin. Phys., 2000, 9 (11): 827-832 doi: 10.1088/1009-1963/9/11/006
Full Text: [PDF 238 KB] (Downloads:375)
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We have observed lasing from the rim of dye-doped ethylene glycol pendant drops. Spatial-resolved spectral measurements show that the lasing wavelength varies along a vertical rim of the drop. Time-resolved measurements indicate that lasing precession occurs within the drop. Various lasing patterns due to lasing precession are explained. The measured precession periods for different pumping points are in good agreement with the calculated values based on morphology-dependent resonance theory.
ATOMIC AND MOLECULAR PHYSICS

THE POTENTIAL MODEL INVESTIGATION OF STARK EFFECT IN CAESIUM RYDBERG STATE ATOMS AND COMPARISON WITH EXPERIMENT

Hu Zheng-fa, Zhao Hong-tai, Zhou Shi-kang, Gong Shun-sheng, Zhan Ming-sheng
Chin. Phys., 2000, 9 (11): 805-809 doi: 10.1088/1009-1963/9/11/002
Full Text: [PDF 260 KB] (Downloads:448)
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The potential model method for computation of Stark structure of Cs Rydberg states atoms and oscillator strength is described, for external electric fields varying from 0 to 600V/cm. Anticrossing, l-mixing and n-mixing phenomena are observed clearly from the map of Stark. Corresponding experiment is performed under the same condition, and the two results are in good agreement with each other within the experimental uncertainty.

APPROXIMATE MODEL OF INTENSE FIELD STABILIZATION FOR HYDROGEN ATOM

Xie Bai-song
Chin. Phys., 2000, 9 (11): 810-812 doi: 10.1088/1009-1963/9/11/003
Full Text: [PDF 169 KB] (Downloads:355)
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An approximate model is proposed to study the stabilization problem of hydrogen atoms under monochromatic intense laser field. The stabilization regime for system parameters such as laser field strength, laser field frequency and atomic magnetic quantum number are obtained by stability analysis of fixed points of the model. The results are consistent with those obtained by other methods.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

ACCURATE DETERMINATION OF FILM THICKNESS BY LOW-ANGLE X-RAY REFLECTION

Xu Ming, Yang Tao, Yu Wen-xue, Yang Ning, Liu Cui-xiu, Mai Zhen-hong, Lai Wu-yan, Tao Kun
Chin. Phys., 2000, 9 (11): 833-836 doi: 10.1088/1009-1963/9/11/007
Full Text: [PDF 217 KB] (Downloads:1758)
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A modified Bragg law for straightforward determining the film thickness by low-angle X-ray reflection was derived based on the geometrical optical theory. We showed that this modified Bragg law and its inference formulae could be used to accurately determine the thickness of the monolayer or multilayer film. Furthermore, the modified Bragg law for determining the superlattice period presented earlier by others can be derived from the above modified Bragg law. The similar inference formulae were also given. The precision in determining the film thickness and/or superlattice period by the above formulae was discussed.

A NEW METHOD TO ALIGN LIQUID CRYSTAL MOLECULES BY LINEAR PHOTO-POLYMERIZATION FOR LIQUID CRYSTAL DISPLAY

Liang Zhao-yan, Fang Kun, Xuan Li, Huang Xi-min, Ding Bao-quan, Lu Ran, Zhao Ying-ying
Chin. Phys., 2000, 9 (11): 837-840 doi: 10.1088/1009-1963/9/11/008
Full Text: [PDF 1807 KB] (Downloads:459)
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A new technique to uniformly align liquid crystal molecules is presented. The technique is based on producing an anisotropic surface on the glass substrate coated with photo-polymers by photo-polymerization of linear polarized UV-light. The orientation of liquid crystal molecules is governed by the direction of the polarized vector of UV-light. Using this method, we have studied the photo-polymer PSi-CM aligning LC 6710A molecules. The liquid crystal microscopic texture between crossed polarizers, optical retardation from liquid crystal layers and electro-optical properties of twisted nematic liquid crystal display cell are obtained, which was prepared with one side -photo-alignment and the other side-rebbed substrate.

OBSERVATION OF PHOTOREFRACTIVE EFFECT OF KNbO3 CRYSTAL AT μW ILLUMINATION

Li Qi, Xia Zong-huang, Lu Xi-ting, Wang Feng, Gong Qi-huang, Shen De-zhong
Chin. Phys., 2000, 9 (11): 841-843 doi: 10.1088/1009-1963/9/11/009
Full Text: [PDF 187 KB] (Downloads:365)
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The photorefractive effects of the as-grown and proton-implanted KNbO3 crystals were studied by two-wave mixing at 62.2μW/cm2 illumination. At this pump power level, the as-grown crystal showed little photorefractive effect, while the proton-implanted crystal showed an obvious effect. Furthermore, there seemed to exist two photorefractive gratings with response times of 22.54 and 1596.30s, at 62.2μW/cm2 pump power level, in the proton-implanted sample. This phenomenon has been attributed to the influence of proton-implantation.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

EFFECT OF DIELECTRIC CONSTANT ON THE EXCITON GROUND STATE ENERGY OF CdSe QUANTUM DOTS

Hui Ping
Chin. Phys., 2000, 9 (11): 844-847 doi: 10.1088/1009-1963/9/11/010
Full Text: [PDF 198 KB] (Downloads:950)
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The B-spline technique is used in the calculation of the exciton ground state energy based on the effective mass approximation (EMA) model. The exciton is confined in CdSe microspherical crystallites with a finite-height potential wall (dots). In this approach, (a) the wave function is allowed to penetrate to the outside of the dots; (b) the dielectric constants of the quantum dot and the surrounding material are considered to be different; and (c) the dielectric constant of the dots are size-dependent. The exciton energies as functions of radii of the dots in the range 0.5-3.5 nm are calculated and compared with experimental and previous theoretical data. The results show that: (1) The exciton energy is convergent as the radius of the dot becomes very small. (2) A good agreement with the experimental data better than other theoretical results is achieved. (3) The penetration (or leaking) of the wave function and the difference of the dielectric constants in different regions are necessary for correcting the Coulomb interaction energy and reproducing experimental data. (4) The EMA model with B-spline technique can describe the status of excition confined in quantum dot very well.

NUMERICAL STUDY ON TUNNELING SPLITTING IN BIAIXAL SPIN SYSTEMS

Chen Zhi-de, Zhang Shu-qun
Chin. Phys., 2000, 9 (11): 848-854 doi: 10.1088/1009-1963/9/11/011
Full Text: [PDF 271 KB] (Downloads:311)
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Numerical study on tunneling splitting in biaxial spin systems is done by performing diagonalization of the Hamilton operator. It is found that the calculated energy splitting agrees quantitatively with theoretical prediction of instanton method. Our result shows that both the instanton method and the large spin limit work well for the total spin around 10. By including the fourth-order term in Hamiltonian, experimental observation can be re-covered quantitatively.
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