Table of contents

15 November 2000, Volume 9 Issue 11 Previous issue    Next issue

GENERAL

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EFFECTS OF NON-CONSERVATIVE FORCES ON LIE SYMMETRIES AND CONSERVED QUANTITIES OF A LAGRANGE SYSTEM Zhang Rui-chao (张睿超), Chen Xiang-wei (陈向炜), Mei Feng-xiang (梅凤翔) Chinese Physics, 2000, 9 (11):  801-804.  DOI: 10.1088/1009-1963/9/11/001 Abstract ( 1325 )   PDF (171KB) ( 625 )   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.

ATOMIC AND MOLECULAR PHYSICS

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THE POTENTIAL MODEL INVESTIGATION OF STARK EFFECT IN CAESIUM RYDBERG STATE ATOMS AND COMPARISON WITH EXPERIMENT Hu Zheng-fa (胡正发), Zhao Hong-tai (赵宏太), Zhou Shi-kang (周士康), Gong Shun-sheng (龚顺生), Zhan Ming-sheng (詹明生) Chinese Physics, 2000, 9 (11):  805-809.  DOI: 10.1088/1009-1963/9/11/002 Abstract ( 1256 )   PDF (260KB) ( 556 )   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.

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APPROXIMATE MODEL OF INTENSE FIELD STABILIZATION FOR HYDROGEN ATOM Xie Bai-song (谢柏松) Chinese Physics, 2000, 9 (11):  810-812.  DOI: 10.1088/1009-1963/9/11/003 Abstract ( 1231 )   PDF (169KB) ( 448 )   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.

CLASSICAL AREAS OF PHENOMENOLOGY

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THEORY OF INTERBAND COHERENCE AND INVERSIONLESS BISTABILITY IN SEMICONDUCTOR LASERS Ge Guo-qin (葛国勤), Leung Pui Tang (梁培) Chinese Physics, 2000, 9 (11):  813-823.  DOI: 10.1088/1009-1963/9/11/004 Abstract ( 1553 )   PDF (310KB) ( 487 )   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.

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EFFECT OF SPHERICAL ABERRATION INTRODUCED BY WATER SOLUTION ON TRAPPING FORCE Yao Xin-cheng (姚新程), Li Zhao-lin (李兆霖), Guo Hong-lian (郭红莲), Cheng Bing-ying (程丙英), Han Xue-hai (韩学海), Zhang Dao-zhong (张道中) Chinese Physics, 2000, 9 (11):  824-826.  DOI: 10.1088/1009-1963/9/11/005 Abstract ( 1253 )   PDF (210KB) ( 584 )   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.

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LASING FROM A DYE-DOPED PENDANT DROP AND ITS PRECESSION Pu Xiao-yun (普小云), Lee Wing-Kee (李荣基) Chinese Physics, 2000, 9 (11):  827-832.  DOI: 10.1088/1009-1963/9/11/006 Abstract ( 1201 )   PDF (238KB) ( 552 )   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.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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ACCURATE DETERMINATION OF FILM THICKNESS BY LOW-ANGLE X-RAY REFLECTION Xu Ming (徐明), Yang Tao (杨涛), Yu Wen-xue (于文学), Yang Ning (杨宁), Liu Cui-xiu (刘翠秀), Mai Zhen-hong (麦振洪), Lai Wu-yan (赖武彦), Tao Kun (陶琨) Chinese Physics, 2000, 9 (11):  833-836.  DOI: 10.1088/1009-1963/9/11/007 Abstract ( 1498 )   PDF (217KB) ( 2265 )   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.

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A NEW METHOD TO ALIGN LIQUID CRYSTAL MOLECULES BY LINEAR PHOTO-POLYMERIZATION FOR LIQUID CRYSTAL DISPLAY Liang Zhao-yan (梁兆颜), Fang Kun (方鲲), Xuan Li (宣丽), Huang Xi-min (黄锡珉), Ding Bao-quan (丁保全), Lu Ran (卢然), Zhao Ying-ying (赵英英) Chinese Physics, 2000, 9 (11):  837-840.  DOI: 10.1088/1009-1963/9/11/008 Abstract ( 1363 )   PDF (1807KB) ( 567 )   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.

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OBSERVATION OF PHOTOREFRACTIVE EFFECT OF KNbO3 CRYSTAL AT μW ILLUMINATION Li Qi (李旗), Xia Zong-huang (夏宗璜), Lu Xi-ting (卢希庭), Wang Feng (王锋), Gong Qi-huang (龚旗煌), Shen De-zhong (沈德忠) Chinese Physics, 2000, 9 (11):  841-843.  DOI: 10.1088/1009-1963/9/11/009 Abstract ( 1141 )   PDF (187KB) ( 457 )   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

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EFFECT OF DIELECTRIC CONSTANT ON THE EXCITON GROUND STATE ENERGY OF CdSe QUANTUM DOTS Hui Ping (惠萍) Chinese Physics, 2000, 9 (11):  844-847.  DOI: 10.1088/1009-1963/9/11/010 Abstract ( 1177 )   PDF (198KB) ( 1117 )   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.

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NUMERICAL STUDY ON TUNNELING SPLITTING IN BIAIXAL SPIN SYSTEMS Chen Zhi-de (陈芝得), Zhang Shu-qun (张树群) Chinese Physics, 2000, 9 (11):  848-854.  DOI: 10.1088/1009-1963/9/11/011 Abstract ( 1357 )   PDF (271KB) ( 391 )   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.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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CONSTRUCTION OF AN OPTICAL TWEEZERS—CALCULATION AND EXPERIMENTS Sun Wei (孙巍), Wang Yi-qiu (王义遒), Gao Chong-ming (高崇明) Chinese Physics, 2000, 9 (11):  855-860.  DOI: 10.1088/1009-1963/9/11/012 Abstract ( 950 )   PDF (262KB) ( 577 )   We report the construction of an optical tweezers system and the results of the trapping and the moving of living algal cells. Experimental study on trapping polystyrene spheres demonstrates the effects of the system parameters on the trap. The trapping forces on dielectric spheres are calculated using Ashkin's ray-optics model. The result shows that an objective with higher numerical aperture can build a more stable trap along axial direction than an objective with lower numerical aperture, though their transverse trapping forces are on the same order.