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991.
The infrared and visible cooperative emissions of ytterbium ions are studied in Yb-doped NdVO4 single crystals. The absorption of optical phonons allows the emissions at room temperature when a Nd:YAG laser is used. Low temperature emissions are observed due to the Nd3+→Yb3+ energy transfer following an argon ion laser excitation of the Nd3+ ions. Analysis of the cooperative emission at low doping concentration (1%) indicates that it is generated by distant pair forming Yb3+ ions while at high doping concentration (≥ 5%) close ions magnetically coupled and superexchange mechanisms prevail in the emitting process. 相似文献
992.
The attenuation of the transverse vibration of a plate, subjected to a harmonic force, is studied. This goal can be achieved by using an active dynamic absorber. The active absorber is made of a pair of piezoelectric sheets, attached to both sides of the plate, and closed electric circuits. One piece of the piezoelectric material provides a sensor for detecting the motion of the plate. Another piece serves as an active dynamic absorber. The equations of motion of the composite plate, including the plate and the piezoelectric material, and the circuit equations of the sensor and the absorber are derived. The displacements of the plate and the currents in the circuits are calculated. The active absorber can successfully attenuate the vibration. The numerical results show that the proposed active absorber can offer more reduction than that using a passive absorber while the absorber is designed to suppress the resonance of a particular vibration mode. Moreover, the active absorber can also reduce the displacements corresponding to other uncontrolled modes. The effects of altering various parameters of the active absorber are studied and discussed. 相似文献
993.
Magnetic properties and magnetocaloric effects of amorphous and crystalline TbCuAl ribbons are investigated by measuring their ac susceptibilities including a nonlinear term and dc magnetizations. The in-phase third harmonic ac susceptibility is found to be negative. It can be well fitted by the expression at high temperatures, indicating a spin-glass behavior in amorphous TbCuAl alloy. ΔTf(ω)/[Tf(ω)Δlog10ω], a possible distinguishing criterion to judge the presence of a spin-glass behavior is ∼0.011. The frequency-dependent data can be well fitted by the conventional critical slowing down law and the spin-glass transition temperature is obtained to be 20.1 K. The maximum of magnetic entropy change reaches 4.5 J kg−1 K−1 for a field change of 0-50 000 Oe, while the crystalline TbCuAl compound experiences a simple ferromagnetic-to-paramagnetic phase transition. The peak value of magnetic entropy change is obtained at the Curie temperature and reaches 14.4 J kg−1 K−1 for the same field change, which is much larger than that of amorphous TbCuAl alloy. 相似文献
994.
The pressure-induced disproportionation reaction of LaH2 was investigated by infrared reflection and Raman measurements at ambient temperature. The relative reflection intensity in the 4000-6000 cm−1 region began to decrease significantly at a pressure of about 12 GPa and fell to 10% of the initial value at 20 GPa. Absorption peaks, which appeared around 1200 and 700 cm−1 at pressures above 14 GPa, were assigned to the hydrogen vibrations at the tetrahedral and octahedral sites of the fcc metal lattice, respectively. The peak frequencies measured in the 14-30 GPa range were similar to those observed in LaH3. These infrared results indicated insulating LaH3 precipitated from metallic LaH2. Above 20 GPa, a Raman peak related to the hydrogen vibration in the octahedral sites appeared around 700 cm−1, and was likely due to lattice distortion. The disproportionation reaction of LaH2 into and solid solution LaHx (x<1) was confirmed. 相似文献
995.
Based on the phenomenological Landau-Devonshire theory, we investigate the film thickness dependence of ferroelectric and electro-optic properties of epitaxial BaTiO3 thin films grown on SrTiO3 and MgO substrates. By using the effective substrate lattice parameter concept, the film thickness dependence of misfit strain is incorporated into the theory. Therefore, the film thickness dependence of ferroelectric and electro-optic properties in epitaxial BaTiO3 thin films can be explained. Moreover, a large quadratic electro-optic effect was obtained in the BaTiO3 thin films, which is in good agreement with the experimental result of BaTiO3 thin films on the MgO substrate. 相似文献
996.
In this paper, we report two crystals Tm:YLF laser pumped by a fiber coupled diode laser with total power of 180 W at 792
nm. When the incident power reached up to 117.0 and 37.3 W of the emission wave-length at 1.91 μm was achieved. Through linear
fit, the corresponding slope efficiency of 38.5%, optical-to-optical conversion efficiency of 31.9% and the beam quality factor
of M
2 ∼ 1.1 were obtained, indicating nearly diffraction limited beam propagation. To our best knowledge, this is the best beam
quality among the reported paper results under the similar experiments. 相似文献
997.
L. Zhang Y. G. Wang H. J. Yu S. B. Zhang W. Hou X. C. Lin J. M. Li 《Laser Physics》2011,21(12):2072-2075
We report on a passively mode-locked Nd:YVO4 laser using a novel graphene oxide saturable absorber fabricated by vertical evaporation method. An 880 nm LD pump source
was used to reduce the thermal load of the laser crystal. At the pump power of 7.4 W, 1.2 W average output power of continuous
wave mode-locked laser with optical conversion efficiency of 16.2% was achieved. To the best of our knowledge, this is the
highest output power of passively mode-locked solid-state laser using graphene oxide saturable absorber. The repetition rate
of passively mode-locked pulse was 88 MHz with the pulse energy of 13.6 nJ. 相似文献
998.
T.Nakagawa M.Kidera Y.Higurasi J.Ohnishi T.Kageyama T.Aihara A.Goto Y.Yano 《中国物理 C》2007,31(Z1):133-136
We measured the main plasma parameters(density of electron,temperature of electron and ion confinement time)and beam intensity of various heavy ions as a function of B_(min).The B_(min) strongly affects the field gradient at the resonance zone,consequently the plasma parameters and beam intensity are changed. Based on these experimental results,we started to construct new 18GHz ECRIS and make a detailed design of the 28GHz SC-ECRIS for RIKEN RI beam factory project. 相似文献
999.
T. Saito T. Nakano H. Hoshizuki K. Sakai Y. Tatematsu S. Mitsudo I. Ogawa T. Idehara V. E. Zapevalov 《International Journal of Infrared and Millimeter Waves》2007,28(12):1063-1078
A 300 GHz CW gyrotron FU CW I has been developed and installed in the Research Center for Development of Far-Infrared Region,
University of Fukui as a power source of a high frequency material processing system. Its performance was tested and the maximum
power of 1.75 kW / CW has been attained at the beam voltage of 15 kV and the beam current of 1A. The maximum window power
efficiency of 15.5% has been obtained at the cathode voltage slightly lower than 15 kV. This gyrotron is designed to deliver
a Gaussian beam after mode conversion from the oscillation mode TE22,8 in the cavity with a complex of an internal radiator and beam shaping mirrors. The detailed measurement with an infrared
camera has confirmed that a Gaussian beam is radiated when the magnetic field strength B
c
at the cavity is adjusted at a proper value. However, within a range of B
c
, the output power is emerged into multiple directions, which suggests simultaneous oscillation of competing cavity modes. 相似文献
1000.
R. Yimnirun A. Ngamjarurojana R. Wongmaneerung S. Wongsaenmai S. Ananta Y. Laosiritaworn 《Applied Physics A: Materials Science & Processing》2007,89(3):737-741
The temperature scaling of the ferroelectric hysteresis was investigated in hard lead zirconate titanate (PZT) bulk ceramic.
The power-law temperature scaling relations were obtained for hystersis area 〈A〉, remnant polarization Pr, and coercivity EC in the forms of 〈A〉∝T-0.9650, Pr∝T-0.0261, and EC∝T-0.8823, respectively, which are mostly comparable to those of its soft counterpart. The observation that Pr decayed more slowly with temperature than in soft PZT was attributed to the presence of the complex defects in hard PZT.
However, the product of Pr and EC still provided the similar scaling law on the T dependence in comparison with 〈A〉.
PACS 77.80.-e; 77.80.Fm; 77.84.-s; 77.84.Dy 相似文献