中国物理B

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GENERALIZED SIEGMAN FORMULA AND COMMENTS ON THE INEQUALITY M²≥1 FOR LIGHT-BEAM QUALITY

盛正卯, 杨焕雄

1999 (2): 81-88. doi: 10.1088/1004-423X/8/2/001

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An generalized version of the Siegman formula which comes directly from Helmholtz equation is reported in this paper. Based on this formula, a comparison between the two definitions of the light beam far-field divergence angle is made. It is discovered the Siegman's moment definition for divergence angle would not make sense if the light beam could not be approximated to the slowly varying one. The proof of inequality M²≥1 given by Chen and Qiu would fail if the evanescence wave effects are considered.

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MULTIPHOTON INTERACTION OF A TWO-LEVEL ATOM WITH A LARGE PERIOD QUANTIZED STANDING WAVE FIELD BEYOND THE RAMAN-NATH REGIME

王晓光, 于荣金

1999 (2): 89-96. doi: 10.1088/1004-423X/8/2/002

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A model that describes the multiphoton interaction of a two-level atom with a large period quantized standing wave field beyond the Raman-Nath regime is solved exactly by the Wei-Norman's operator factorization method, and the momentum distribution of the atom is discussed. We also investigate the dynamics of the atomic population inversion and field second-order correlation function. They exhibit very remarkable behavior due to the inclusion of atomic translational motion.

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SCREENING EFFECT OF THE SPIN DISTRIBUTION IN THE ATOMS OF HYDROGEN AND ALKALI METALS UNDER THE DISTURBANCE OF A STRONG PERIODIC MAGNETIC FIELD

张忠灿, 胡陈果, 方祯云

1999 (2): 97-108. doi: 10.1088/1004-423X/8/2/003

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Using the path integral method, we calculated all the distribution probability ratios for the spin projection of the electron in a hydrogen atom under the disturbance of a strong periodic magnetic field, and studied the screening effect of the coupling of spin with the periodic magnetic field B(t) on the ratios of the spin distributions. It is found that the screening exists not only in the usual direction along the magnetic field (not affected by initial conditions) but also other directions affected by the initial conditions. For the valence electron in the alkali metals, such as ^{3/sup>Li, ¹¹Na, ¹⁹K, ³⁷Ru, and ⁵⁵Ce, etc., a similar conclusion can be drawn.}

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ENTROPY IN DEMIANSKI-NEWMAN BLACK HOLE

万浪辉, 朱建阳

1999 (2): 109-117. doi: 10.1088/1004-423X/8/2/004

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By using the brick-wall model we calculate the free energy and the entropy including the superradiant effect mode of the scalar field in Demianski-Newman black hole. When the radial cut-off factor \barε and the angular cut-off factor δ satisfy a proper relation, the entropy can be written as S=A_H/4.

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A SOLITON PERTURBATION THEORY FOR THE UNSTABLE NONLINEAR SCHR?DINGER EQUATION WITH CORRECTIONS

陈芝得, 陈向军, 黄念宁

1999 (2): 118-130. doi: 10.1088/1004-423X/8/2/005

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Based on the Zakharov-Shabat equation of the inverse scattering transform for the unstable nonlinear Schr?dinger equation, for which a perturbation theory with corrections is developed in this paper. All necessary formulae for calculating the scattering data are derived. Based upon these formulae, the effect due to the corrections can be studied. As an example, the correction due to the damping is calculated.

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A NONLINEAR MODEL FOR HIGHLY EXCITED VIBRATIONAL ENERGY LEVELS OF SILANE

陈向荣, 程艳, 罗俊, 芶清泉, 庞小峰

1999 (2): 131-135. doi: 10.1088/1004-423X/8/2/006

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The highly excited vibrational energy levels of SiH stretches of silane SiH₄ in the electronic ground state are calculated using a three-parameter nonlinear model, i.e., the quantized discrete self-trapping equation. The obtained results are in good agreements with the experimental data and with those obtained from local mode calculations of others. We note that SiH₄ molecule is a typical molecule close to the local mode limit, and that when n≥3, the molecule could be thought of as vibrating with the four SiH stretching quanta trapped into a single SiH bond.

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INTERACTION OF A ∧-TYPE THREE-LEVEL ATOM WITH A TWO-MODE FIELD AND A TWO-MODE RAMAN-COUPLED MODEL

张智明, 何林生, 周士康

1999 (2): 136-142. doi: 10.1088/1004-423X/8/2/007

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The Hamiltonian is derived for the interaction of a ∧-type three-level atom with a two-mode quantum cavity field from the general interaction Hamiltonian between a multi-level atom and a multi-mode radiation field, and it is reduced to an effective two-mode Raman-coupled model under a large detuning condition. We propose a modified effective Hamiltonian for the two-mode Raman-coupled model, find the time-dependent state vectors, and present the validity conditions for the involved interaction Hamiltonians. It is shown that in the study of the two-mode Raman-coupled model it is not enough to retain only the usually used effective Hamiltonian, one must also take into account the ac Stark shift of the atomic levels (at least one of the levels). Finally, we study the atomic dynamics in the interaction of a ∧-type three-level atom with a two-mode quantum cavity field and in the two-mode Raman-coupled model. We find that the number of collapse-revivals, the collapse time and the revival time show new characteristics.

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LINEWIDTH REDUCTION IN AN INVERSIONLESS LASER WITH PUMP PHASE FLUCTUATIONS

胡响明, 彭金生

1999 (2): 143-149. doi: 10.1088/1004-423X/8/2/008

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The effect of the pump phase diffusion on the linewidth of a laser without inversion is studied. It is shown that the linewidth at equal intensity may be reduced below that for a coherent driving, enen if the net effect of the pump bandwidth leads to an increase in the linewidth. The physical mechanism is analyzed in the dressed-state picture. Furthermore, the effects of the pump phase noise on the linewidths of an inversionleess laser and a Raman laser are compared with each other.

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