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61.
We present numerical models of tri-valence erbium ion and thulium ion-co-doped fiber amplifiers pumped by 800-nm and 980-nm
lasers. The rate and power propagation equations of the models are numerically solved to analyze the gain as a function of
co-doping concentrations, fiber length and signal wavelength. The results reveal that with 800-nm or 980-nm pump, gain competition
exists between 1470- and 1530-nm bands, which may arise from the pump absorption competition and complicated energy transfer
between the two types of active ions, and the results further show that the gain spectra may cover 305 nm (1375–1680 nm) for
800-nm pump and 160 nm (1400–1560 nm) for 980-nm pump. The doping concentrations and fiber length may be tuned to reduce the
ripple of the gain spectra. 相似文献
62.
W. J. Guo Y. F. Lin X. H. Gong Y. J. Chen Z. D. Luo Y. D. Huang 《Applied physics. B, Lasers and optics》2009,94(1):155-163
A Pr3+:NaGd(MoO4)2 single crystal has been grown by the Czochralski method. The polarized absorption spectra, polarized fluorescence spectra,
and fluorescence decay curves of the crystal were measured at room temperature. The Judd–Ofelt intensity parameters Ω
t,q
(t=2,4,6) and the spectroscopic parameters related to the 3
P
0 and 1
D
2 multiplets were obtained and analyzed. The decay mechanisms for the 3
P
0 and 1
D
2 multiplets were also discussed. 相似文献
63.
D. S. L. Pontes E. Longo F. M. Pontes M. S. Galhiane L. S. Santos Marcelo A. Pereira-da-Silva J. H. D. da Silva A. J. Chiquito P. S. Pizani 《Applied Physics A: Materials Science & Processing》2009,96(3):731-740
Ferroelectric Pb1−x−y
Ca
x
Sr
y
TiO3 thin films (denoted by PCST90, PCST70, and PCST30) were deposited on the Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. Their properties were investigated from the viewpoint of crystal
structure, microstructure, dielectric, and ferroelectric properties. X-ray diffraction patterns revealed the formation of
PCST90, PCST70, and PCST30 thin films without any secondary phases. Infrared and Raman spectroscopy results show that a gradual
phase transition from tetragonal to pseudocubic or cubic perovskite structure may occur in PCST thin films with the simultaneous
increase of Ca2+ and Sr2+ contents. Both substitution of isovalent Ca2+ and Sr2+ at Pb2+-site enhanced the dielectric constant and reduced the remnant polarization. In addition, ferroelectric test analyses show
that the PCST thin films undergo a ferroelectric-to-paraelectric phase transformation with an amount of Pb2+, Ca2+, and Sr2+ at 30%, 35%, and 35% mol, respectively. Hence, the absence of ferroelectric property may be attributed to a decreasing of
the octahedron distortion in the perovskite structure accompanied by a weakening of long-range ferroelectric order. 相似文献
64.
F. Pfuner J. G. Analytis J.-H. Chu I. R. Fisher L. Degiorgi 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(4):513-517
We report on a thorough optical investigation of BaFe2As2 over a broad spectral range and as a function of temperature, focusing our attention on its spin-density-wave (SDW) phase
transition at TSDW = 135 K. While BaFe2As2 remains metallic at all temperatures, we observe a depletion in the far infrared energy interval of the optical conductivity
below TSDW, ascribed to the formation of a pseudogap-like feature in the excitation spectrum. This is accompanied by the narrowing of
the Drude term consistent with the dc transport results and suggestive of suppression of scattering channels in the SDW state.
About 20% of the spectral weight in the far infrared energy interval is affected by the SDW phase transition. 相似文献
65.
Studies on 2,4-DNT Mixtures Using Reflection Terahertz Time Domain Spectroscopy for Explosives Detection 下载免费PDF全文
Absorption spectra (0.2-1.8 THz) of the mixtures of explosive 2,4-DNT and polyethylene(PE) at different ratios are obtained using reflection terahertz time domain spectroscopy (THz-TDS). The pronounced absorption peak of 2,4-DNT at 1.08 THz is always observed for the mixtures with 2,4-DNT ratios above 20%. Experimental results demonstrate that more applicable and realistic THz-TDS in reflection geometry can be used to distinguish explosive mixed with other material having no THz fingerprints, and has a high potential in the detection of explosives. 相似文献
66.
Two new modes of generating spiral pairs in an excitable medium have been found. They depend on a geometrical structure (GS) inside the medium. This may be formed e.g. as a result of scars or fibrosis in the heart tissue, or artificially built in a chemical reaction substrate. Both sources involve a GS composed of a circular “convergent lens” bounded by two opaque “walls”. One mode can be induced by a single wave and behaves as a “flip-flop” type of a limit cycle. The other mode is generated by a train of plane waves impinging on the GS, and is created at the focus of the converging wave-fragments. 相似文献
67.
We present experimental measurements and theory of the diffusely backscattered Mueller matrix patterns that arise from illuminating a turbid medium with a polarized laser beam. Our technique employs polarized light from a He-Ne laser (λ=632.8nm) focused onto the surface of the scattering medium. A surface area of approximately 2×2 cm2 centred on the light input point is imaged through polarization analysis optics onto a CCD camera. The Mueller matrix is reconstructed by 49 intensity measurements with various orientations of polarizer and analyser. The measured Mueller matrix of polystyrene spheres is compared with the theory result of incoherent scattering of light by spheres. It shows that the azimuthal patterns of the Mueller matrix are determined by the symmetry of the turbid media and the shape of scattering particles. The result is further proved by experiments with polystyrene spheres of different concentrations in de-ionized water. 相似文献
68.
The motivation of this theoretical work is to introduce a model calculation for the elastic waves scattering and coherent phonon transport at an atomic nanojunction between face-centered cubic (fcc) leads. The model system A/B consists of two perfect semi-infinite fcc leads A and B, oriented in the same direction and joined by an atomic interface. It is applied to the system Cu/Ni and its inverse Ni/Cu. A theoretical approach based on the matching method is used to study the dynamics of the system A/B. 相似文献
69.
M. Jelínek W. Kulisch M.P. Delplancke-Ogletree J. Lancok L. Jastrabík D. Chvostová C. Popov J. Bulír 《Applied Physics A: Materials Science & Processing》2001,73(2):167-170
Nitrogen-rich carbon nitride films were prepared by three different deposition methods on fused silica, stainless steel and
silicon cantilever substrates. Their optical properties were studied by spectroscopic ellipsometry and UV spectrometry. Mechanical
properties such as plastic and Vickers microhardness, Young’s modulus, adhesion and film stress were also tested. The results
were compared with the properties of films with lower nitrogen concentrations.
Received: 26 January 2001 / Accepted: 29 January 2001 / Published online: 3 May 2001 相似文献
70.
F. Bassani V. Lucarini 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):567-573
We use the Kubo response function formalism to derive the asymptotic behaviour of the harmonic generation susceptibilities
to all orders n. The results show a stringent correspondence with the ones previously obtained from the classical anharmonic oscillator model.
They are characterized by a dependence and a coefficient proportional to the trace of the (n+1)th derivative of the potential energy on the equilibrium density matrix. Using the above results we derive new Kramers-Kr?nig
relations and sum rules for all orders of harmonics susceptibilities.
Received 17 April 2000 相似文献