Table of Content

20 February 1998, Volume 7 Issue 2 Previous Issue    Next Issue

GENERAL

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OPTIMUM DURATION OF MEASUREMENT FOR REDUCING THERMAL NOISE LIMITATIONS IN TORSION PENDULUM EXPERIMENTS HU ZHONG-KUN, LUO JUN 1998, 7 (2):  81-88.  doi: 10.1088/1004-423X/7/2/001 Abstract ( 0 )   PDF (232KB) ([an error occurred while processing this directive])   Statistical estimates of thermal noise fluctuation of a linear harmonic oscillator used to detect weak forces are reexamined with special reference to gravitational experiments. Thermal noise limitation on the measurement of displacement of an oscillator is studied. It is found that the signal response of an oscillator reaches the maximum value while the thermal noise response reaches the minimum value at the same time during the transient state of the oscillator, and the precision of the experiments in the transient state could increase about two orders higher than that in the equilibrium state for typical experiments. It is also found that there is an optimum duration of measurement in which the uncertainty due to thermal noise in this period is the least.

ATOMIC AND MOLECULAR PHYSICS

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CHAOTIC BEHAVIOR OF A ONE-DIMENSIONAL MODEL ATOM IN AN INTENSE FIELD LIU JIE, CHEN SHI-GANG, BAMBI HU 1998, 7 (2):  89-105.  doi: 10.1088/1004-423X/7/2/002 Abstract ( 0 )   PDF (489KB) ([an error occurred while processing this directive])   In this paper we describe the rescattering process in optical field ionization through a one-dimensional model, which improves the well-known quasistatic model by adding the smoothed Coulomb potential in its second step. The above-threshold ionization spectra and high-order harmonic generation are calculated from this model. They are qualitatively in agreement with the quantum results and experiments. In particular, we find that this model is charact erized by chaotic scattering. Modern nonlinear theory is used to analyze this dy namical system. It is found that singular self-similar fractal structure exists in the phase-dependence energy spectra, and the unstable manifolds constitute the chaotic scattering pattern. Our results also demonstrate a close connection of irregular trajectories with the energy spectra and high-order harmonic gener ation. We conclude that the chaotic behavior plays an important role in this one-dimensional model of optical field ionization.

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DYNAMIC NUCLEAR POLARIZATION OF ORGANIC COMPOUND DOPED WITH FREE RADICALS YANG BAO-LIAN, FENG JI-WEN, ZHOU JIAN-WEI, LI LI-YUN, YE CHAO-HUI, HU JIAN-ZHI, RONALD J.PUGMIRE, DAVID M.GRANT 1998, 7 (2):  106-114.  doi: 10.1088/1004-423X/7/2/003 Abstract ( 0 )   PDF (247KB) ([an error occurred while processing this directive])   For those organic compounds which lack free radicals, a doping approach named melting-liquid-nitrogen-quench was developed in order to perform dynamic nuclear polarization(DNP)-nuclear magnetic resonance experiments. By using this method, the 1H, 13C, 15N DNP enhancements were observed with free-radical-doped dibenzofuran and benzamide. The enhancement mechanism and relation between the concentration of unpaired electrons and the maximum DNP enhancement are discussed.

CLASSICAL AREAS OF PHENOMENOLOGY

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QUANTUM CORRELATION IN PHOTOREFRACTIVE THREE WAVE MIXING: SEMICLASSICAL APPROACH Lü YA-JUN, WU LING-AN, ZHANG PEI-LIN, LI SHI-QUN 1998, 7 (2):  115-125.  doi: 10.1088/1004-423X/7/2/004 Abstract ( 0 )   PDF (438KB) ([an error occurred while processing this directive])   Quantum fluctuations of the fields for three-wave mixing in photorefractive media with drift nonlinearity and nonlocal response are investigated, using a semiclassical input-output theory. It is shown that quantum cor relation and anticorrelation among the three modes will change according to the relative intensity ratio and the direction of energy transfer between the signal and reference modes. The fluctuations in the intensity difference of the two signal modes can be reduced below the corresponding shot-noise level.

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INFLUENCE OF BEAM POLARIZATION ON THE PERFORMANCE OF A MUTUALLY PUMPED PHASE CONJUGATOR GAO HONG, DOU SHUO-XING, CHI MING-JUN, SONG HONG-WEI, ZHU YONG, YE PEI-XIAN 1998, 7 (2):  126-133.  doi: 10.1088/1004-423X/7/2/005 Abstract ( 0 )   PDF (187KB) ([an error occurred while processing this directive])   The influence of polarization variation of a pump beam on the performance of a “bridge” mutually pumped phase conjugator has been investigated. The reflectivity, transmission, and response time were measured for different polarizations and different intensity rations of input beams. From these measured results, the variation behaviors of parameters of fourwave mixing interactions in the crystal are revealed.

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ACOUSTIC ABSORPTION CHARACTERISTICS OF FOAMED ALUMINUM HAN FU-SHENG, ZHU ZHEN-GANG, LIU CHANG-SONG, ZHENG DA-RUI, CAI XIU-LAN 1998, 7 (2):  134-142.  doi: 10.1088/1004-423X/7/2/006 Abstract ( 0 )   PDF (266KB) ([an error occurred while processing this directive])   The acoustic absorption characteristics of foamed aluminum and the effect of its structural parameters on the characteristics have been in vestigated. The results indicate that the acoustic absorption behavior of foamed aluminum has an uncertain relation with its porosity, the effect of pore size is non-monotonous, while the flow resistance, which characterizes the structural coefficients, might be the most important factor. It is also found that the absorption peak is widened and the noise reduction coefficient can be increased through suitable compressive deformation.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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ON THE GENERATION OF LASER-INDUCED PLASMA ACOUSTIC WAVES NI XIAO-WU, ZOU BIAO, CHEN JIAN-PING, BIAN BAO-MIN, SHEN ZHONG-HUA, LU JIAN, CUI YI PING 1998, 7 (2):  143-147.  doi: 10.1088/1004-423X/7/2/007 Abstract ( 0 )   PDF (128KB) ([an error occurred while processing this directive])   In this paper, the transition of laser plasma waves into laser plasma acoustic waves has been discussed first, and it is suggested that the weak limitation of laser-induced-plasma shock wave is an acoustic wave. Based on this idea, a definition of laser plasma acoustic wave is given, and this kind of acoustic waves for some materials has been obtained experimentally.