中国物理B

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OPTIMUM DURATION OF MEASUREMENT FOR REDUCING THERMAL NOISE LIMITATIONS IN TORSION PENDULUM EXPERIMENTS

胡忠坤, 罗俊

1998 (2): 81-88. doi: 10.1088/1004-423X/7/2/001

摘要 ( 1106 )

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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.

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CHAOTIC BEHAVIOR OF A ONE-DIMENSIONAL MODEL ATOM IN AN INTENSE FIELD

刘杰, 陈式刚, BAMBI HU

1998 (2): 89-105. doi: 10.1088/1004-423X/7/2/002

摘要 ( 1432 )

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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

杨保联, 冯继文, 周建威, 李丽云, 叶朝辉, 胡建治, RONALD J.PUGMIRE, DAVID M.GRANT

1998 (2): 106-114. doi: 10.1088/1004-423X/7/2/003

摘要 ( 1326 )

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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.

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QUANTUM CORRELATION IN PHOTOREFRACTIVE THREE WAVE MIXING: SEMICLASSICAL APPROACH

吕亚军, 吴令安, 张培林, 李师群

1998 (2): 115-125. doi: 10.1088/1004-423X/7/2/004

摘要 ( 1119 )

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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

高宏, 窦硕星, 迟明军, 宋宏伟, 朱镛, 叶佩弦

1998 (2): 126-133. doi: 10.1088/1004-423X/7/2/005

摘要 ( 1130 )

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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

韩福生, 朱震刚, 刘长松, 郑大瑞, 蔡秀兰

1998 (2): 134-142. doi: 10.1088/1004-423X/7/2/006

摘要 ( 1048 )

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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.

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ON THE GENERATION OF LASER-INDUCED PLASMA ACOUSTIC WAVES

倪晓武, 邹彪, 陈建平, 卞保民, 沈中华, 陆建, 崔一平

1998 (2): 143-147. doi: 10.1088/1004-423X/7/2/007

摘要 ( 1397 )

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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.

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