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Tunnelling of Two-Level Atoms in Two-Photon Mazer: Atomic Coherence Effect and Statistics of Cavity Fields
HE Xiao-Ling, DU Si-De, ZHOU Lu-Wei, WANG Qi-Sheng, CHEN Hao
Chin. Phys. Lett. 2004, 21 (1):
18-21
.
Tunnelling of a two-level atom is investigated in the two photon mazer when the atom is initially prepared in a coherent superposition state and the cavity in various quantum states. For a strong coherent field, the tunnelling exhibits more regular oscillations but less remarkable switch effect than that in the one-photon mazer. It is discovered that in the presence of atomic coherence, the transmission probabilities in the ultracold regime are significantly different when the cavity field is initially in coherent, squeezed vacuum, even cat and odd cat states, respectively.
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Phase Transition of Hot Nuclear Matter
LI Zeng-Hua, ZUO Wei, LU Guang-Cheng
Chin. Phys. Lett. 2004, 21 (1):
29-32
.
Based on the difference between the Fermi distributions at zero temperature and at the finite temperature, we introduce the temperature-dependent three-body force (TBF) into the microscopic finite-temperature Brueckner-Hartree-Fock theory (FTBHF). In terms of the meson-exchange current approach, i.e. the one boson exchange (OBE) approximation, the exchange of four important mesons π, ρ, σ and ω are considered. Using the FTBHF theory including TBF, we describe the critical temperature of the liquid-gas phase transition for symmetric nuclear matter and discuss its change trend with the increasing asymmetry parameter. Compared to the result excluding TBF, the value of the critical temperature turns out to be smaller.
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Chemical Equilibration and Dilepton Production of Quark-Gluon Plasma at RHIC Energies
LONG Jia-Li, HE Ze-Jun, MA Guo-Liang, MA Yu-Gang, LIU Bo
Chin. Phys. Lett. 2004, 21 (1):
47-50
.
An evolution model of the chemically equilibrating quark-gluon plasma system has been established based on the Jüttner distribution function of partons. By studying the dilepton production of the system, we find that due to high initial temperature, a dominant contribution to dileptons with intermediate masses is provided by gluon density of the system as well as large gluon fusion gg → cc cross section in the intermediate mass region, quark--antiquark annihilation qq → ll and, especially, thermal charmed quarks from the gluon fusion gg → cc and quark--antiquark annihilation qq → cc.
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Application of 41Ca Tracer and Its AMS Measurement in
CIAE
DONG Ke-Jun, HE Ming, WU Shao-Yong, YUE Dong-Fang, YOU Qu-Bo, BAO Yi-Wen, GUAN Yong-Jing, ZHENG Yuan-Feng, YIN Xin-Yi, WANG Hui-Juan, LI Guo-Qiang, YANG Yao-Yun, XU Guo-Ji, HU Yue-Ming, JIANG Shan
Chin. Phys. Lett. 2004, 21 (1):
51-53
.
The man-made calcium isotope 41Ca is an ideal tracer for the study of calcium metabolism. We represent the first application of accelerator mass spectrometry (AMS) measurement of 41Ca tracer in China. The technique is being applied to the research field of cell messenger at the China Institute of Atomic Energy (CIAE). The sample preparation methods and the AMS measurements are discussed and some interesting results are presented.
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Theoretical Analysis of Generalized Oscillator Strengths for Helium by R-Matrix Method
HAN Xiao-Ying, VoKy Lan, LI Jia-Ming,
Chin. Phys. Lett. 2004, 21 (1):
54-56
.
The high-energy electronic-impact excitation cross section is directly proportional to the generalized oscillator strength (GOS) of the target atom. The generalized oscillator strengths of helium atom from the ground state to the excited states (21S, 21P and 31D) are calculated using the updated R-matrix codes within the first Born approximation. Our calculation results are in good agreement with the previous theoretical and experimental results at high incident energies. In order to treat the bound-bound and bound-continuum transitions in a unified manner, the GOS density is defined based on the quantum defect theory. We calculate the GOS densities of 1S, 1P and 1D channels, namely the complete high-energy collision cross sections of electronic-impact excitations into all the n1S, n1P and n1D excited states. In addition to high-energy excitation cross sections, a scheme to calculate the excitation cross sections for entire incident energy range is discussed.
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Structural Phase Transformations of ZnS Nanocrystalline Under High Pressure
PAN Yue-Wu, QU Sheng-Chun, GAO Chun-Xiao, HAN Yong-Hao, LUO Ji-Feng, CUI Qi-Liang, LIU Jing, ZOU Guang-Tian
Chin. Phys. Lett. 2004, 21 (1):
67-69
.
In-situ energy dispersive x-ray diffraction on ZnS nanocrystalline was carried out under high pressure by using a diamond anvil cell. Phase transition of wurtzite of 10 nm ZnS to rocksalt occurred at 16.0 GPa, which was higher than that of the bulk materials. The structures of ZnS nanocrystalline at different pressures were built by using materials studio and the bulk modulus, and the pressure derivative of ZnS nanocrystalline were derived by fitting the equation of Birch-Murnaghan. The resulting modulus was higher than that of the corresponding bulk material, which indicates that the nanomaterial has higher hardness than its bulk materials.
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Experimental and Theoretical Analysis of Nondegenerate Ultrabroadband Chirped Pulse Optical Parametric Amplification
LIU Hong-Jun, ZHAO Wei, CHEN Guo-Fu, WANG Yi-Shan, YU Lian-Jun, RUAN Chi, LU Ke-Qing
Chin. Phys. Lett. 2004, 21 (1):
94-97
.
Experimental investigations of nondegenerate ultrabroadband chirped pulse optical parametric amplification have been carried out. The general mathematical expressions for evaluating parametric bandwidth, gain and gain bandwidth for arbitrary three-wave mixing parametric amplifiers are presented. In our experiments, a type-I noncollinear phase-matched optical parametric amplifier based on lithium triborate, which was pumped by a 5-ns second harmonic pulses from a Q-switched Nd:YAG operating at 10 Hz, seeded by a 14-fs Ti:sapphire laser at 800 nm, was presented. The 0.85 nJ energy of input chirped signal pulse with 57-FWHM has been amplified to 3.1 μJ at pump intensity 3 GW/cm2, the corresponding parametric gain reached 3.6 x 103, the 53 nm-FWHM gain spectrum bandwidth of output signal has been obtained. The large gain and broad gain bandwidth, which have been confirmed experimentally, provide great potentials to amplify efficiently the broad bandwidth femtosecond light pulses to generate new extremes in power, intensity, and pulse duration using optical parametric chirped pulse amplifiers pumped by powerful nanosecond systems.
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Low-Threshold Mid-Infrared Optical Parametric Oscillator Using
Periodically Poled LiNbO3
LIN Xue-Chun, ZHANG Ying, KONG Yu-Peng, ZHANG Jie, YAO Ai-Yun, HOU Wei, CUI Da-Fu, LI Rui-Ning, XU Zu-Yan, LI Jian
Chin. Phys. Lett. 2004, 21 (1):
98-100
.
We report the generation of tunable mid-infrared optical pulses using all-solid-state pumped optical parametric oscillator in a periodically poled lithium niobate. Several ways were used to lower the threshold, resulting in a mean threshold as low as 6.5 mW and an achievement of wavelength conversion in the 2.77-4.04 μm spectral range. Continuous tuning range from 2.97 to 3.25 μm was achieved. The maximum idler output power of 466 mW at the wavelength of 3.41 μm was obtained, which represents an optical-to-optical conversion efficiency of 19% from incident pump power to the idler output.
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Electromagnetic Instabilities Excited by Electron Temperature Anisotropy
LU Quan-Ming, WANG Lian-Qi, ZHOU Yan, WANG Shui
Chin. Phys. Lett. 2004, 21 (1):
129-132
.
One-dimensional particle-in-cell simulations are performed to investigate the nonlinear evolution of electromagnetic instabilities excited by the electron temperature anisotropy in homogeneous plasmas with different parameters. The results show that the electron temperature anisotropy can excite the two right-hand electromagnetic instabilities, one has the frequency higher than Ωe, the other is the whistler instability with larger amplitude, and its frequency is below Ωe. Their dispersion relations are consistent with the prediction from the cold plasma theory. In the initial growth stage (prediction from linear theory), the frequency of the dominant mode (the mode whose amplitude is large enough) of the whistler wave almost does not change, but in the saturation stage the situation is different. In the case that the ratio of electron plasma frequency to cyclotron frequency is larger than 1, the frequency of the dominant mode of the whistler wave drifts from high to low continuously. However, for the case of the ratio smaller than 1, besides the original dominant mode of the whistler wave whose frequency is about 2.6 ωe, another dominant mode whose frequency is about 1.55 ωe also begins to be excited at definite time, and its amplitude increases with time until it exceeds the original dominant mode.
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Linear and Nonlinear Optical Properties of Quasicrystals
ZHOU Xiang, HU Cheng-Zheng, GONG Ping, ZHU Jia-Kun
Chin. Phys. Lett. 2004, 21 (1):
140-142
.
An investigation is carried out on the linear and nonlinear optical properties of quasicrystals. The linear and nonlinear susceptibilities are determined for two- and three-dimensional quasicrystals. The results show that for optical linearity, two-dimensional quasicrystals are uniaxial, while icosahedral quasicrystals are optically isotropic. Meanwhile all quasicrystals, except those with 5, 5 m, N, Nmm (N = 8, 10, 12) symmetries, have no the first-order optical nonlinearity. The tensor scheme of the first-order nonlinear susceptibility is the same for these eight exceptional kinds of quasicrystals.
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Thermal Stability and Spectroscopic Properties of Yb:Zinc-Tungsten-Tellurite Glass
WANG Guo-Nian, XU Shi-Qing, YANG Jian-Hu, DAI Shi-Xun, ZHANG Jun-Jie, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2004, 21 (1):
173-175
.
New multi-component Yb:zinc--tungsten--tellurite glasses (70TeO2-(20-x) ZnO-xWO3-5La2O3-2.5 K2O-2.5Na2O-1.0 Yb2O3 (x = 0, 15 mol%) have been presented. Thermal stability and spectroscopic properties of Yb3+ ions have been measured. The results show that TZW2 glass (x = 15 mol%) has thermal stability (Tx - Tg > 160°C with Tx being the onset crystallization temperature and Tg the glass transition temperature) better than TZN glass and that the stimulated emission cross-section of 1.32 pm2 for the 2F5/2 → 2F7/2 transition is higher than other laser glasses (QX, ADY, LY and FP), with the measured fluorescence lifetime of 0.93 ms and the broad fluorescence effective linewidth of 74.5 nm. Evaluated from the good potential laser parameters, TZW2 glass with both the minimum pump intensity (0.92 kW/cm2) and gain parameter (1.23 pm2ms) is promising for miniature solid fibre lasers or high-peak power lasers, as well as tunable lasers.
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Coherent Excitonic Wavepackets in Two-Dimensional Square Dot Arrays Driven by an In-Plane Uniform Electric Field
LI Xiu-Ping, YAN Wei-Xian,
Chin. Phys. Lett. 2004, 21 (1):
197-200
.
We investigate the evolution behaviour of electron-hole pair wavepacket in optically excited square quantum-dot arrays driven by in-plane (x-y plane) uniform electric field E (viz, E = Exex + Eyey, ex, ey are unit vectors along x and y directions respectively), in the time domain. It is found that if the ratio of the x-component electric field Ex to the y-component electric field Ey is a rational p/q (p and q being coprime integer numbers), the wavepackets undergo a time-periodic breathing mode, with the period 2πp/ωBx, where ωBx = eExa/ħ, with a being the lattice constant of square dot arrays, ħ being Planck's constant, e being the electron charge. This finding provides a time-domain demonstration of the recent spectral result [Phys. Rev. Lett. {86} (2001) 3116].
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Field Emission from Silicon Nanocrystallite Films with Compact Alignment and Uniform Orientation
YU Ke, WANG Wei-Ming, ZHU Zi-Qiang, ZHANG Yong-Sheng, YU Xian-Wen, CHEN Shao-Qiang, LI Qiong, YANG Guang-Da, ZHU Jian-Zhong, CHEN Qun, LU Wei, ZI Jian
Chin. Phys. Lett. 2004, 21 (1):
203-206
.
Patterned silicon nanocrystallite (SiNC) films were fabricated on (100) orientation p-type boron-doped silicon wafer by the hydrogen ion implantation technique and the anodic etching method. The efficient field emission with low turn-on field of about 3.5 V/μm at current density of 0.1 μA/cm2 was obtained. The emission current density from the SiNC films reached 1 mA/cm2 under a bias field of about 9.1 V/μm. The experimental results demonstrate that there are great potential applications of the SiNC films for flat panel displays. A surface treatment with hydrogen plasma was performed on the SiNC films and a significant improvement of emission properties was achieved.
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64 articles
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