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Analysis of Runaway Evaporation and Bose--Einstein Condensation by Time-of-Flight Absorption Imaging
CHEN Shuai, ZHOU Xiao-Ji, YANG Fan, XIA Lin, SUN Ya-Ya, WANG Yi-Qiu, CHEN Xu-Zong,
Chin. Phys. Lett. 2004, 21 (11):
2105-2108
.
The achievement of Bose--Einstein condensation (BEC) in our experiment is reported. The process of BEC formation is observed by detecting the image after free expansion, in which the effectiveness of runaway evaporative cooling is shown by measuring the optical density of the atom cloud. About 2×105 87Rb atoms in the |F=2,mF=2> state are condensed into the condensate. The ratio of axial-to-radial size of the condensate released from the magnetic trap is investigated in theory and experiment.
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Investigation of Exotic Structure of the Largely Deformed Nucleus 23Al in the Relativistic-Mean-Field Model
CHEN Jin-Gen, , CAI Xiang-Zhou, WANG Ting-Tai, MA Yu-Gang, REN Zhong-Zhou, FANG De-Qing, ZHONG Chen, WEI Yi-Bin, GUO Wei, ZHOU Xing-Fei, , WANG Kun, MA Guo-Liang, TIAN Wen-Dong, ZUO Jia-Xu, MA Chun-Wang, CHEN Jin-Hui, YAN Ting-Zhi, SHEN Wen-Qing
Chin. Phys. Lett. 2004, 21 (11):
2140-2143
.
A candidate for proton halo nucleus 23Al is investigated based on the constrained calculations in the framework of the deformed relativistic mean field (RMF) model with the NL075 parameter set. It is shown by the constrained calculations that the ground state of 23Al has a large deformation that corresponds to the prolate shape. With that large deformation, the non-constrained RMF calculation predicts that there appears an inversion between the 2s1/2 [211] and 1d5/2 [202] shells. The valence proton of 23Al is weakly bound and occupies 2s1/2 [211] and 1d5/2 [202] with the weights of 56% and 29%, respectively. The calculated RMS radius for matter is in agreement with the experimental one. It is also predicted that the difference between the proton RMS radius and the neutron one is very large. This suggests that there exists a proton halo in 23Al.
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Two-Quasiparticle Bands and Isomers in 98Sr
LI Ming-Liang, ZHU Sheng-Jiang, J. H. Hamilton, A. V. Ramayya, J. K. Hwang, CHE Xing-Lai, ZHANG Zheng, YU
Ying-Nan, ZHENG Ran-Cheng, I. Y. Lee, J. O. Rasmussen, Y. X. Luo, W. C. Ma
Chin. Phys. Lett. 2004, 21 (11):
2147-2150
.
Rotational bands in neutron-rich 98Sr nucleus have been investigated by measuring high-fold prompt λ-ray coincidence events of the spontaneous fission of 252Cf with the Gammasphere detector array. A deformed K=3 band built on the 1838 keV level has been confirmed and extended. Another deformed K=6 band based on the 2535keV level has been established. Both the bands originate most probably from the v 2/9[404] v2/3[411] two-quasiparticle configuration with Ω=|Ω1-Ω2|and Ω=|Ω1- Ω2|, respectively. Based on the delay-coincidence measurements, the half-lives for the K=3 and K=6 band head levels have been obtained to be 13±3 ns and 4.5± 1.0 ns, respectively.
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Quasielastic Scattering of the Halo Nucleus 6He at 25 MeV/u from a 9Be Target
PANG Dan-Yang, YE Yan-Lin, JIANG Dong-Xing, ZHENG Tao, WANG Quan-Jin, LI Zhi-Huan, LI Xiang-Qing, GE Yu-Cheng, WU Cui-E, ZHANG Gao-Long, HU Qing-Yuan, WANG Jia, A. Ozawa, Y. Yamaguchi, R. Kanungo, D. Fang, I.Tanihata
Chin. Phys. Lett. 2004, 21 (11):
2151-2154
.
The differential cross sections of quasielastic scattering of a 25MeV/u 6He from 9Be target have been measured. The double-folding model approach is applied to generate the real part of the optical potential. The imaginary potential parameters as well as some of the real potential parameters are studied in comparison with the experimental data. The effect of the unstable nucleus is discussed.
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Surface-Induced Melting of Metal Nanoclusters
YANG Quan-Wen, ZHU Ru-Zeng, WEI Jiu-An, WEN Yu-Hua
Chin. Phys. Lett. 2004, 21 (11):
2171-2174
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We investigate the size effect on melting of metal nanoclusters by molecular dynamics simulation and thermodynamic theory based on Kofman’s melt model. By the minimization of the free energy of metal nanoclusters with respect to the thickness of the surface liquid layer, it has been found that the nanoclusters of the same metal have the same premelting temperature Tpre=T0-T0(γsv-γlv-γsl)/(ρLξ) (T0 is the melting point of bulk metal, γsv the solid--vapour interfacial free energy, γlv the liquid--vapour interfacial free energy, γsl the solid--liquid interfacial free energy, ρ the density of metal, L the latent heat of bulk metal, and ξ the characteristic length of surface-interface interaction) to be independent of the size of nanoclusters, so that the characteristic length ξ of a metal can be obtained easily by Tpre, which can be obtained by experiments or molecular dynamics (MD) simulations. The premelting temperature Tpre of Cu is obtained by MD simulations, then ξ is obtained. The melting point Tcm is further predicted by free energy analysis and is in good agreement with the result of our MD simulations. We also predict the maximum premelting-liquid width of Cu nanoclusters with various sizes and the critical size, below which there is no premelting.
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High Efficiency Continuous-Wave Tm:Ho:GdVO4 Laser Pumped by a Diode
YAO Bao-Quan, HE Wan-Jun, WANG Yue-Zhu, ZHANG Xing-Bao, LI Yu-Feng
Chin. Phys. Lett. 2004, 21 (11):
2182-2183
.
We report a high efficiency cw diode-pumped cryogenic Tm(5at.%), Ho(0.5at.%):GdVO4 laser. The pumping source is a fibre-coupled laser diode with fibre core diameter of 0.4mm and numerical aperture of 0.3, supplying power 14.8W at 793.6nm. For input pump power of 13.6W at 794.2nm, the maximum output power of 4.2W, optical-to-optical conversion efficiency of 31% and slope efficiency 38% have been attained at 2.0485μm. To our knowledge, the operating performance is the best among the previously reported Tm:Ho:GdVO4 lasers. We also analyse the influence of pump wavelengths (from 792 nm to 794.2 nm) on the output power, the optical-to-optical conversion efficiency increases with the longer pump wavelength which is closer to the absorption peak of 797 nm in Tm,Ho:GdVO4.
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Diode-Pumped Self-Starting Mode-Locked Nd:YVO4 Laser with Semiconductor Saturable Absorber Output Coupler
JIA Yu-Lei, WEI Zhi-Yi, ZHENG Jia-An, LING Wei-Jun, WANG Yong-Gang, MA Xiao-Yu, ZHANG Zhi-Gang
Chin. Phys. Lett. 2004, 21 (11):
2209-2211
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By using a semiconductor saturable-absorber output coupler as a mode-locking device, we experimentally realized the operation of a diode-pumped passively mode-locked Nd:YVO4 laser. Stable laser pulses with duration of 2.3ps were generated at the output power of about 1W. With increasing the pump power to 9 W, the maximum mode-locked power of 1.7 W was obtained, which corresponds to a slope conversion efficiency of 44% and optical-to-optical conversion efficiency of 19%.
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Analysis of Photosensitivity of Copolymer Optical Fibre Preform
MA Hui, LI Zeng-Chang, MING Hai, ZHANG Qi-Jin, TAM Hwa-Yaw, ZHANG Yong-Sheng, ZHANG Tao, WANG Pei, XIE Jian-Ping
Chin. Phys. Lett. 2004, 21 (11):
2252-2254
.
The photosensitivity of copolymer optical fibre preform is analysed in comparison with the doped one. The effects of write conditions such as pump power and pump time have been studied. Then, the preform is drawn into single mode polymer optical fibre with core refractive index of 1.499, and core-cladding refractive-index difference of 0.008. Long-period birefringence gratings with period of 120um are fabricated in the fibre. The duty cycle is 50%, and the refractive index change in the exposed area is about 1×10-3.
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Electron Transport of an Impurity Quantum Wire Under THz Electromagnetic Field Illumination
LI Yuan, ZHOU Guang-Hui, XIAO Xian-Bo, CHENG Fang, LIAO Wen-Hu
Chin. Phys. Lett. 2004, 21 (11):
2263-2266
.
We theoretically investigate the effect of a single finite-size attractive impurity on the electron transport of a semiconductor quantum wire under the influence of a terahertz electromagnetic field illumination. In the free-particle framework, the time-dependent electronic states are obtained by introducing an unitary transformation, and the electronic transmission of the system is obtained by using the scattering matrix approach. In the case of the field frequency resonant with the lateral energy spacing of the two lowest levels, a step-like structure for the transmission probability versus the total electron energy is predicted. Furthermore, due to the interplay between the single impurity and the applied field, the transmission probability curve in the non-resonant case shows a structure of a resonance dip on the interference pattern background with certain parameters of the impurity.
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Evidence of the Griffiths Phase in Doped Manganites Studied by Electron Paramagnetic Resonance Measurements
YUAN Song-Liu, LIU Sheng, CAO Heng, SHANG Jing-Lin, DONG Bo, XIA Zheng-Cai, LI Jian-Qing
Chin. Phys. Lett. 2004, 21 (11):
2285-2288
.
A systematic investigation of electron paramagnetic resonance above the Curie temperature Tc is performed on polycrystalline (La1-xYx)x2/3Ca1/3MnO3 (x=0, 0.15 and 0.2) samples. The results indicate anomalous paramagnetic behaviour below a temperature TG and, the anomalous extent
increases with cooling from TG. Especially, the resonance linewidth ΔHpp anomalously increases with cooling for the temperature range of TCG. The experimental observation is discussed within the framework of the Griffiths theory that predicts the existence of ferromagnetic clusters above TC. We explain the observed anomalous paramagnetic behaviour to be due to the magnetic heterogeneity caused by the ferromagnetic clusters which appear in the Griffiths phase.
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Frequency Upconversion Emission of Er3+-Doped Strontium--Lead--Bismuth Glasses
SUN Hong-Tao, DAI Shi-Xun, XU Shi-Qing, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2004, 21 (11):
2292-2294
.
Er3+-doped strontium--lead--bismuth glasses for developing potential upconversion lasers have been fabricated and characterized. Under 975 nm excitation, intense green and red emissions centred at 525, 546, and 657 nm, corresponding to the transitions 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2, respectively, were observed at room temperature. The upconversion mechanisms are discussed based on the energy matching and quadratic dependence on excitation power, and the dominant mechanisms are excited state absorption and energy transfer upconversion for 525 and 546nm emissions, and energy transfer upconversion for 657nm emission.
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Red Organic Light-Emitting Diodes Utilizing a Novel Metal Complex as the Host Material
WEI Peng, QIAO Juan, GAO Yu-Di, WANG Li-Duo, QIU Yong
Chin. Phys. Lett. 2004, 21 (11):
2298-2300
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Red organic light-emitting diodes (OLEDs) utilizing a novel metal complex with a tridentate ligand, salicylidene-o-aminophenolato (8-quinolinoato) aluminium (Al(Saph-q)) as the host material, have been fabricated. In the OLEDs, N,N’-bis-(1-naphthyl)-N,N’-diphenyl-1,1’-biphenyl-4,4-’diamine (NPB) and 4-(dicyanomethylene)-2-(t-butyl)6-methyl-4H-pyran (DCJTB) are used as the hole-transporting and dopant materials, respectively. Compared with the OLEDs using tris(8-quinolinolato) aluminium (Alq3) as the host material, improved device performance with higher efficiency (0.62lm/W) has been achieved, in the consideration that developing host materials is a promising way to achieve excellent red emission OLEDs.
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Photoluminescence Characterization of Nanocrystalline ZnO Array
CHANG Yong-Qin, YU Da-Peng, LI Guo-Hua, FANG Zai-Li, ZHANG Ye, CHEN Yao-Feng, YANG FU-Hua
Chin. Phys. Lett. 2004, 21 (11):
2301-2304
.
High-density and uniform well-aligned ZnO sub-micron rods are synthesized on the silicon substrate over a large area. The morphology and structure of the ZnO sub-micron rods are investigated by x-ray diffraction, transmission electron microscopy and Raman spectra. It is found that the ZnO sub-micron rods are of high crystal quality with the diameter in the range of 400--600 nm and the length of several micrometres long. The optical properties were studied by photoluminescence spectra. The results show that the intensity of the ultraviolet emission at 3.3 eV is rather high, meanwhile the deep level transition centred at about 2.38 eV is weak. The free exciton emission could also be observed at low temperature, which implies the high optical quality of the ZnO sub-micron rods. This growth technique provides one effective way to fabricate the high crystal quality ZnO nanowires array, which is very important for potential applications in the new-type optoelectronic nanodevices.
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Ultrafast Photoelectric Effects in Heterojunctions of La0.7Sr0.3MnO3 and Si
Lü Hui-Bin, JIN Kui-Juan, HUANG Yan-Hong, HE Meng, ZHAO Kun, ZHOU Yue-Liang, CHENG Bo-Lin, CHEN Zheng-Hao, DAI Shou-Yu, YANG Guo-Zhen
Chin. Phys. Lett. 2004, 21 (11):
2308-2309
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Ultrafast photoelectric effects have been observed in p--n heterojunctions of La0.7Sr0.3MnO3(LSMO)/Si and LSMO/SrTiO3-/Si for the first time. The rise time was about 1 ns and the full width at half maximum was about 2 ns for the photovoltaic pulse when the heterojunction was irradiated by a laser of ~25 ps pulse duration and 1064 nm wavelength. The photovoltaic sensitivity was as large as 435 mV/mJ for a 1064 nm laser pulse. No such pulse was observed with irradiation from a pulsed 10.6 μm CO2 laser.
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A Novel Magnetic Linear Encoder Designed by Using the Slant Multi-Phase Filtering Model
SHI Yu, XING Huai-Zhong, ZHANG Huai-Wu, LIU Ying-Li, JING Yu-Lan, ZHONG Zhi-Yong
Chin. Phys. Lett. 2004, 21 (11):
2310-2312
.
A novel design model based on the slant multi-phase filtering model is presented. A magnetic linear encoder with sinusoidal output voltage waveform has been investigated, and the improved sinusoidal output waveform can be easily acquired. A minimum 6% of distortion factor, when the difference of slant phase is 2π/3, is observed. It is found that the Wheatstone bridge type sensor, made of NiFe(450A)/NiO(300A) bilayers deposited on Si (001) substrate, can enhance both output signal and thermal stability, and then can be widely used in the field of magneto-resistive sensor.
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68 articles
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