Table of contents

20 February 1997, Volume 6 Issue 2 Previous issue    Next issue

ATOMIC AND MOLECULAR PHYSICS

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AN APPROACH OF ESTIMATING EXCITATION CROSS SECTIONS IN MULTIPHOTON PROCESSES RAN QIN (冉琴), ZHANG LI-MIN (张立敏), DAI JING-HUA (戴静华), MA XING-XIAO (马兴孝) Acta Physica Sinica (Overseas Edition), 1997, 6 (2):  81-91.  DOI: 10.1088/1004-423X/6/2/001 Abstract ( 1215 )   PDF (306KB) ( 367 )   We suggest a simple approach to roughly estimate the excitation cross sections of various steps in a multiphoton ionization (or dissociation) process by applying the measured dependence of product signal on laser intensity. The validity of this method is demonstrated theoretically by means of the rate equations based upon a two-step kinetic model and can, in principle, be extended to the multiphoton process with steps more than two. Some results of numerical test and experiment are quoted.

CLASSICAL AREAS OF PHENOMENOLOGY

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LASING WITHOUT INVERSION AND ORIGIN OF GAIN IN A $\Lambda$ SYSTEM ZHANG DENG-YU (张登玉) Acta Physica Sinica (Overseas Edition), 1997, 6 (2):  92-96.  DOI: 10.1088/1004-423X/6/2/002 Abstract ( 1025 )   PDF (91KB) ( 350 )   A three-level $\Lambda$-type atomic system is pumped by an incoherent radiation field. The system lases without population inversion in the steady state. We analyze the inversionless gain and origin of the gain.

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COHERENT POPULATION TRAPPING IN THE SYSTEM OF A $\varLambda$-CONFIGURATION MULTILEVEL ATOM DRIVEN BY A TWO-MODE QUANTIZED FIELD LI GAO-XIANG (李高翔), PENG JIN-SHENG (彭金生) Acta Physica Sinica (Overseas Edition), 1997, 6 (2):  97-109.  DOI: 10.1088/1004-423X/6/2/003 Abstract ( 1194 )   PDF (386KB) ( 387 )   We have studied the atomic coherent population trapping in the system of a two-mode quantized field interacting with a $\varLambda$-configuration multilevel atom with one lower discrete state mad two sets of quasicontinuum states, or a set of quasicontinuum states and a set of true continuum states. The influence of the atom's initial preparation and the properties of the atomic upper levels on whether or not atomic coherent population trapping occurs, and the states of the field which trap the atom are analyzed.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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ION FLUX BEHAVIOR IN HIGH DENSITY PLASMAS SHAO FU-QIU (邵福球), WANG LONG (王龙), WU HAN-MING (吴汉明), YAO XIN-ZI (姚鑫兹) Acta Physica Sinica (Overseas Edition), 1997, 6 (2):  110-124.  DOI: 10.1088/1004-423X/6/2/004 Abstract ( 1138 )   PDF (438KB) ( 458 )   The available electron cyclotron resonance plasma sources have been simulated in two-dimensional configuration space (Z, R) and three-dimensional velocity space (Vz, Vr, V$\theta$). Using a hybrid model, we treat ions as particles and electrons as fluid. The simulation is specified for plasma parameters of the available apparatus and is focused on the ion flux distributions. For a set of given operating conditions, the spatial distributions of electron temperature, plasma potential, plasma density, ionization rate and the contours map of distributions of particles in different volume cells in velocity space are obtained; statistics on ions that hit the bottom surface are also reported. The distributions of ion flux vectors on different cross-section planes in the plasma are given, and the phenomena of large radial diffusione of ions across magnetic force lines are also demonstrated. Finally, the influences of microwave power and neutral gas pressure on the distributions of ion flux vectors on ZR-plane, ion flux radial distributions and ion currents to all walls have been studied.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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INVESTIGATION OF GROWTH CHARACTERISTICS OF MONOCRYSTALLINE C60 FILMS IN HELIUM GAS ENVIRONMENT MA GUO-BIN (马国斌), YANG YING-HU (杨映虎), CHEN GUANG-HUA (陈光华) Acta Physica Sinica (Overseas Edition), 1997, 6 (2):  125-129.  DOI: 10.1088/1004-423X/6/2/005 Abstract ( 1301 )   PDF (170KB) ( 369 )   The growth characteristics of C60 films were investigated in helium gas environment at pressures of 0, 2.667×10-2 and 6.667×10-2 Pa, respectively. X-ray diffraction results showed that perfectly (111) oriented monocrystalline C60 films with large grains were successfully deposited on synthetic 1M phlogopite mica-fluorophlogopite (0Ol) plane at a substrate temperature of 160℃ when the helium gas pressure is 2.667×10-2 Pa. The results indicated that under appropriate helium gas pressure, the energy change of C60 molecules through collisions with helium atoms, and the decrease of the supersaturation of the vapor pressure in the vicinity of the substrate resulted in a quasi-thermodynamic equilibrium deposition system. As a result, well-structured monocrystalline C60 films were deposited on (001) plane of the fluorophlogopite substrate.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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YBaCuO BICRYSTAL JUNCTIONS AND DC SUPERCONDUCTING QUANTUM INTERFERENCE DEVICES WANG SHI-GUANG (王世光), DAI YUAN-DONG (戴远东), ZENG XIANG-HUI (曾祥辉), ZHENG PEI-HUI (郑培辉), CHEN MING-LING (陈名玲), WANG SHOU-ZHENG (王守证), XIONG GUANG-CHENG (熊光成), LIAN GUI-JUN (连贵君), GAN ZI-ZHAO (甘子钊) Acta Physica Sinica (Overseas Edition), 1997, 6 (2):  130-139.  DOI: 10.1088/1004-423X/6/2/006 Abstract ( 1294 )   PDF (284KB) ( 423 )   We have prepared yttria-stabilized-zirconia bicrystal substrates using a simple hot-pressing method. The grain-boundary junctions have been fabricated with YBa2Cu3O7 thin films grown epitaxially on the bicrystals. The patterns are defined by conventional photolithography, The dc and microwave characteristics of the junctiorts and the dc superconducting quantum interference devices (SQUIDs) have been intensively studied. The current-voltage curves are bridge-typed with noise rounding near the critical current. Resistive tail has been observed in the resistance versus temperature curves. The results are compared with the theoretical prediction for classical Josephson junctions. It is found that the behavior of bicrystal junctions can be described in the frame of classical theory. The deviations are attributed to the nonuniformity of the junctions. The small loop dc SQUIDs demonstrate diffraction and interference effects with regard to the applied magnetic field. A large square-washer with a new configuration has been designed to enhance the effective area of dc SQUID as a magnetometer. It has achieved a magnetic field resolution down to 1 pT/(Hz)1/2(at 10Hz) at 77K.

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PHOTOCHROMISM AND ITS MECHANISM IN POLYDIACETYLENE CRYSTALS PENG JING-CUI (彭景翠) Acta Physica Sinica (Overseas Edition), 1997, 6 (2):  140-150.  DOI: 10.1088/1004-423X/6/2/007 Abstract ( 1218 )   PDF (296KB) ( 375 )   Based on summarizing and analyzing experimental facts of photochromism in polydiacetylene crystals, a theoretical model describing the photochromic process was presented. It is considered that the photochromism is the result of phase structural conversion during photoexcitation excitonic relaxation process, and its dependence on the energy and density of incident photons can be explained correctly. The micro-mechanism of photochromism is discussed in detail.