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91.
D.-L. Zhang C. Wu Q.-Z. Yang L. Sun Y.-H. Xu E. Y. B. Pun 《Applied physics. B, Lasers and optics》2009,95(2):335-340
Transient characteristics of upconverted emission (560 nm) of Er3+ in LiNbO3 crystals codoped with 0–7.4 mol% MgO were studied under pulse excitation at 800-nm wavelength. The results show that the
transients display considerable Mg-doping-level-dependent nonexponential behavior and a clear Mg optical-damage-resistance
threshold concentration effect. Below the Mg threshold concentration, the lifetime increases slightly with the increased Mg
concentration. Above the threshold, however, the lifetime drops abruptly by 4–7 times and the nonexponential feature becomes
more evident. It is found that each transient can be fitted by a double-exponential function contributed from isolated and
clustered Er3+ sites. The fit parameters show that doping of MgO above the threshold concentration increases the clustered Er site concentration
and the nonradiative cross relaxation probability. The Mg threshold concentration effect derived from the transients is in
qualitative agreement with that from the fluorescence spectrum measured as a function of the Mg concentration. The effect
of the Mg threshold concentration on the clustered Er site concentration is qualitatively explained on the basis of the microscopic
defect model of MgO:LiNbO3 and is conducted with the Mg site change around the threshold concentration. 相似文献
92.
V. K. Rai 《Applied physics. B, Lasers and optics》2009,95(2):329-333
Upconversion luminescence in triply ionized praseodymium-doped TeO2–Li2O glass using excitation at ∼590 nm into the 1D2 level from a dye laser pumped with the second harmonic of a pulsed Nd:YAG laser has been reported. The mechanism involved
in the upconversion emission observed at ∼480 nm indicates that the most important contribution is energy transfer among praseodymium
ions in pairs followed by the dipole–dipole interaction. The rate-equation model for the emission at ∼480 nm that provides
direct information to determine the energy-transfer rates containing the pair of states involved in the upconversion process
has been explored. 相似文献
93.
A. A. Sirotkin L. Di Labio A. I. Zagumennyi Yu. D. Zavartsev S. A. Kutovoi V. I. Vlasov W. Lüthy T. Feurer A. A. Onushchenko I. A. Shcherbakov 《Applied physics. B, Lasers and optics》2009,94(3):375-379
The use of glasses doped with PbS nanocrystals as intracavity saturable absorbers for passive Q-switching and mode locking
of c-cut Nd:Gd0.7Y0.3VO4, Nd:YVO4, and Nd:GdVO4 lasers is investigated. Q-switching yields pulses as short as 35 ns with an average output power of 435 mW at a repetition
rate of 6–12 kHz at a pump power of 5–6 W. Mode locking through a combination of PbS nanocrystals and a Kerr lens results
in 1.4 ps long pulses with an average output power of 255 mW at a repetition rate of 100 MHz. 相似文献
94.
This study presents a novel approach for analyzing the interaction between two parallel surfaces grafted with polymer brushes
in a good solvent. In the proposed approach, MD simulations are performed to establish the mean brush height and the standard
deviation of the brush height distribution for a given value of the surface separation. The corresponding probability density
function (PDF) of the brush height is then determined both with and without the assumption of a brush interpenetration effect,
respectively, and a statistical technique is applied to compute the corresponding interaction free energy per unit area of
the grafted substrates. Finally, the Derjaguin approximation is employed to determine the corresponding value of the interaction
force between the two surfaces. The results obtained for the interaction free energy and interaction force are compared with
those derived using the Alexander and de Gennes (AdG) model and the Milner, Witten and Cates (MWC) model, respectively. The
value of the normalized interaction free energy computed using the present method is higher than that obtained from the AdG
and MWC models at larger surface separations when the brush interpenetration effect is ignored. However, the results obtained
by the current method for the interaction force are found to be in better agreement with the experimental data than those
obtained using the AdG or MWC models. The enhanced performance of the proposed method is attributed primarily to the use of
an adaptive non-Gaussian PDF of the brush height to model the effects of brush interpenetration and fluctuations in the brush
conformation at different distances from the grafting plane. 相似文献
95.
Yi-Sheng Lai Jyh-Liang Wang Sz-Chian Liou Chia-Hsun Tu 《Applied Physics A: Materials Science & Processing》2009,94(2):357-363
In this work, we demonstrate a fast approach to grow SiO2 nanowires by rapid thermal annealing (RTA). The material characteristics of SiO2 nanowires are investigated by field emission scanning electron microscopy, high-resolution transmission electron microscopy
(HRTEM), high-angle annular dark-field (HAADF) imaging, electron energy loss spectroscopy (EELS), and energy-filtered TEM
(EFTEM). The HAADF images show that the wire tip is predominantly composed of Pt with brighter contrast, while the elemental
mappings in EFTEM and EELS spectra reveal that the wire consists of Si and O elements. The SiO2 nanowires are amorphous with featureless contrast in HRTEM images after RTA at 900°C. Furthermore, the nanowire length and
diameter are found to be dependent on the initial Pt film thickness. It is suggested that a high SiO2 growth rate of >1 μm/min can be achieved by RTA, showing a promising way to enable large-area fabrication of nanowires. 相似文献
96.
We present direct measurements of the lifetime of the 4F5/2 and 2H(2)9/2 manifold in Nd3+:YLiF4, using a fluorescence pump-probe technique. The technique populates the 4F5/2 and 2H(2)9/2 manifold directly with a pump pulse. Via excited state absorption from this excited manifold, the 2F(2)5/2 manifold of Nd3+ is populated with a delayed probe pulse. The population in the 4F5/2 and 2H(2)9/2 manifold is monitored as a function of time by observing the change in integrated UV fluorescence from the 2F(2)5/2 manifold for each time delay between pump and probe pulses. The pump and probe beams come from the fundamental and second harmonic wavelengths of a femtosecond Ti:sapphire regenerative amplifier. The measured lifetime agrees well with the energy gap law, based on other nonradiative lifetime measurements from the literature for Nd3+:YLiF4. 相似文献
97.
Yanping Wei Chaoyang Tu Guohua Jia Hongyan Wang Fugui Yang Xiuai Lu Jianfu Li Yan Wang 《Solid State Communications》2006,140(5):230-235
crystal with the size up to Φ 13 mm×44 mm was grown successfully by the Czochralski technique and its optical properties were presented. The absorption cross-section and emission cross-section were presented. Also, the potential laser gain near 1.9 μm was investigated. In the framework of the Judd-Ofelt (J-O) theory, the intensity parameters were calculated to be: Ω2=11.375×10−20 cm2, Ω4=5.077×10−20 cm2 and Ω6=6.524×10−20 cm2. The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetime as well as the branching ratios were calculated, too. This crystal is promising as a tunable infrared laser crystal. 相似文献
98.
99.
This paper investigated on the dehydration of Er3+-doped phosphate glasses using O2 + CCl4 bubble flow method. The influence of parameters of dehydration effect was studied systemically. It was found that the dehydration rate was rather rapidly at the initial stage of bubbling. Increasing gas flow rate and temperature could drive the dehydration process toward lower OH concentration in the melts. The dehydration process was carried out in open system and analyzed by thermodynamic theory of open system, which clarified the process of eliminating of OH groups from the glass melts with bubbling time and gas flow rate. A time-dependent empirical equation about reaction rate constant was derived, and the relationships between rate constant and bubbling flow rate, and temperature were also discussed. This analytical method could be applicable to the dehydration of glass melt using other dehydration agents. 相似文献
100.
We describe a physically associating triblock copolymer-based gel that exhibits a reversible transition between solid and liquid states at a temperature of approximately 55°C. The thermal transition of the gel enables us to compare the properties of liquid suspensions and elastic composites with identical particle loadings, with particle volume fractions as large as 0.55. The suspension viscosity and the composite elasticity scale in a similar manner with the overall particle volume fraction, a result that is rationalized in terms of an effective strain amplification factor that depends only on the particle loading. Measured values of the strain amplification factor are in good agreement with the expected form for well-dispersed spheres. We also find that the elastic composites are exceptionally strong, with fracture strengths that exceed the modulus of the base gel by a factor of 100 or more. Deviations from purely elastic behavior became important for high particle volume fractions, and were probed by stress relaxation experiments. 相似文献