上转换效应对Er3+-Yb3+共掺磷酸盐玻璃被动调Q 激光输出的影响

To study the effects of upconversion in Erbium, a set of rate equations that simulates the performance of the passively Q-switched Er:Yb:glass laser with a Co²⁺:MgAl2O4 saturable absorber was set up. The dynamics of the Er³⁺ excited state and the effect of upconversion on the passively Q-switched laser are obtained through numerical simulation of the model. It is found that the impact ratios of upconversion effect on the peak power of the passively Q-switched laser pluse and the repetition rate are both decreased with the increase of pump power.

Effect of dietary carbohydrate-to-lipid ratios on growth and feed utilization in Chinese longsnout catfish (Leiocassis longirostris Gunther)

An 8-week growth trial was carried out in a semi-recirculation system at 26 +/- 0.5 degrees C to investigate the optimal dietary carbohydrate-to-lipid (CHO:L) ratio for carnivorous Chinese longsnout catfish (Leiocassis longirostris Gunther). Triplicate tanks of fish were assigned to each of five isocaloric and isonitrogenous diets with different carbohydrate-to-lipid ratios (0.75, 1.48, 1.98, 2.99 and 5.07). The results showed that a higher specific growth rate (SGR) and feed rate (FR) were observed in the fish fed diet ratios of 1.98 CHO:L (P < 0.05). Overloading dietary carbohydrate (5.07 CHO:L ratio) caused skeletal malformations. Apparent digestibility of dry matter (ADC(d)) significantly increased with dietary CHO:L ratio (P < 0.05), while significantly higher apparent digestibility of protein (ADC(p)) and apparent digestibility of energy (ACD(e)) was observed only in the 1.98 CHO:L group (P < 0.05). Whole body contents of dry matter, lipid and energy significantly increased as the CHO:L ratio decreased (P < 0.05). The hepatosomatic index (HSI) was highest at 1.98 CHO:L ratio (P < 0.05). Highest dietary CHO:L ratio resulted in lower liver glycogen, liver lipid, plasma glucose and plasma triacylglycerol (P < 0.05), whereas there was no significant difference in plasma total cholesterol (P > 0.05). High dietary CHO:L ratio caused pathological changes in fish morphology and liver histology. Based on maximum growth, the optimal carbohydrate-to-lipid ratio was 1.98 for Chinese longsnout catfish.

Double ionization of helium in collision with 20-500-keV/amu Cq+ and Oq+ (q=1-3) ions

Target ionization and projectile charge changing were investigated for 20-500 keV/u Cq+, Oq++He (q=1-3) collisions. Double- to single-ionization ratios R-21 of helium associated with no projectile charge change (direct ionization), single-electron capture, and single-electron loss were measured. The cross-section ratio R-21 depends strongly on the collision velocity v, the projectile charge state q, and the outgoing reaction channel. Meanwhile, a model extended from our previous work [J. X. Shao, X. M. Chen, and B. W. Ding, Phys. Rev. A 75, 012701 (2007)] is presented to interpret the above-mentioned dependences. Good agreement is found between the model and the experimental data.

One-electron capture with simultaneous ionization in Cq+, Oq+ (q=1-4)-Ar collisions

The ratios R-k1 of k-fold to single ionization of the target atom with simultaneous one-electron capture by the projectile have been measured for 15-480 keV/u (nu(p) = 0.8-4.4 a.u.) collisions of Cq+, Oq+ (q=1-4) with Ar, using time-of-flight techniques which allowed the simultaneous identification of the final charge state of both the low-velocity recoil ion and the high-velocity projectile for each collision event. The present ratios are similar to those for He+ and He2+ ion impact. The energy dependence of R-k1 shows a maximum at a certain energy, E-max. which approximately conforms to the q(1/2)-dependence scaling. For a fixed projectile state, the ratios R-k1 also vary strongly with outgoing reaction channels. The general behavior of the measured data can be qualitatively analyzed by a simple impact-parameter, independent-electron model. (C) 2009 Elsevier B.V. All rights reserved.

Transfer ionization of helium in collisions with Cq+ and Oq+ (q=1-3)

Cross-section ratios sigma(TI)/sigma(SC) of transfer ionization (TI) to single capture (SC) of Cq+- and Oq+-He (q = 1 - 3) collisions in the energy range of 15-440 keV/u (0.8-4.2 v(Bohr)) are experimentally determined. It is shown that sigma(TI)/sigma(SC) strongly depends on the projectile velocity, and there is a maximum for E(keV/u)/q(1/2) approximate to 150. Combining the Bohr-Lindhard model and the statistical model, a theoretical estimate is presented, in reasonable agreement with the experimental data when E(keV/u)/q(1/2) > 35.

L-shell ionization accompanied by one-electron capture in Cq+, Oq+ (q=2,3)-Ne collisions

The L-shell ionization processes of a Ne gas target associated with single-electron capture by bombardment of Cq+ and Oq+ (q=2,3) are investigated using the projectile-recoil-ion coincidence method in the energy range from 80 to 400 keV/u (v(p)=1.8-4 a.u.). The cross-section ratios (R-k1) of k-fold ionization to single capture are compared with the results for He2+-Ne collisions by Dubois [Phys. Rev. A 36, 2585 (1987)]. All the velocity dependences are quite similar. The ratios increase as the projectile energy increases in the lower-energy region, reach the maxima for projectile energies around E-max=160q(1/2) keV/u, and then decrease at higher energies. These results qualitatively agree with our calculations in terms of the Bohr-Lindhard model within the independent-electron approximation.

Double electron processes in collisions of partially stripped ions Cq+ (q=1-4) with helium

The multi-electron processes are investigated for 17.9-120keV/u C1+, 30-323 keV/u C2+, 120-438 keV/u C3+, 287-480keV/u C4+ incident on a helium target. The cross-section ratios of double electron (DE) process to the total of the single electron (SE) and the double electron process (i.e. SE+DE), the direct double electron (DDI) to the direct single ionization (DSI) as well as the contributions of DDI to DE and of TI to DE are measured using coincidence techniques. The energy and charge state dependences of the measured cross-section ratios are studied and discussed.

Thermocapillary Flows In Liquid Bridges Of Molten Tin With Small Aspect Ratios

Numerical simulations were conducted to study thermocapillary flows in short half-zone liquid bridges of molten tin with Prandtl number Pr = 0.009, under ramped temperature difference. The spatio-temporal structures in the thermocapillary flows in short half-zone liquid bridges with aspect ratios As = 0.6, 0.8, and 1.0 were investigated. The first critical Marangoni numbers were compared with those predicted by linear stability analyses (LSA). The second critical Marangoni numbers for As = 0.6 and 0.8 were found to be larger than that for As = 1.0. The time evolutions of the thermocapillary flows exhibited unusual features such as a change in the azimuthal wave number during the three-dimensional stationary (non-oscillating) flow regime, a change in the oscillation mode during the three-dimensional oscillatory flow regime, and the decreasing and then increasing of amplitudes in a single oscillation mode. The effects of the ramping rate of the temperature difference on the flow modes and critical conditions were studied as well. In this paper, the experimental observability of the critical conditions was also discussed. (C) 2008 Elsevier Inc. All rights reserved.

Hydrothermal Instability Of Thermocapillary Convection In Large-Prandtl-Number Liquid Bridges Under Microgravity

Linear stability analysis was performed to study the mechanism of transition of thermocapillary convection in liquid bridges with liquid volume ratios ranging from 0.4 to 1.2, aspect ratio of 0.75 and Prandtl number of 100. 2-D governing equations were solved to obtain the steady axi-symmetric basic flow and temperature distributions. 3-D perturbation equations were discretized at the collocation grid points using the Chebyshev-collocation method. Eigenvalues and eigenfunctions were obtained by using the Q-R. method. The predicted critical Marangoni numbers and critical frequencies were compared with data from space experiments. The disturbance of the temperature distribution on the free surface causes the onset of oscillatory convection. It is shown that the origin of instability is related to the hydrothermal origin for convections in large-Prandtl-number liquid bridges. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

Robust Nanoadhesion Under Torque

In this article, optimization of shear adhesion strength between an elastic cylindrical fiber and a rigid substrate under torque is studied. We find that when the radius of the fiber is less than a critical value, the bonding-breaking along the contact interface occurs uniformly, rather than by mode III crack propagation. Comparison between adhesion models under torque and tension shows that nanometer scale of fibers may have evolved to achieve optimization of not only the normal adhesive strength but also the shear adhesive strength in tolerance of possible contact flaws.

Rayleigh-Marangoni-Bénard Convective Instability

The Rayleigh-Marangoni-Benard convective instability (R-M-B instability) and flow patterns in the two-layer system of silicon oil 10cSt and Fluorinert FC70 liquids are studied theoretically and experimentally. Both linear instability analysis and 2D numerical simulation (A=L/H=10) were performed to study the influence of thermocapillary force on the convective instability of the two-layer system. Time-dependent oscillations arising at the onset of convection were investigated in a larger various range of two-layer depth ratios (Hr=H1/H2) from 0.2 to 5.0 for different total depth less than 12mm. Our results are different from the previous study on the Rayleig-B閚ard instability and show the strong effects of thermocapillary force at the interface on the time-dependent oscillations at the onset of instability convection. Primary experimental results of the critical instability parameters and the convective structure in the R-M-B convection have been obtained by using the digital particle image velocimetry (DPIV) system, and a good agreement in comparison with the results of numerical simulation was obtained.

Research on Q-Switched Nd : YAG laser engraving

IN this paper, the engraving process with Q-Switched Nd:YAG laser is investigated. High power density is the pre- requisition to vapor materials, and high repetition rate makes the engraving process highly efficient. An acousto- optic Q-Switch is applied in the cavity of CW 200 W Nd:YAG laser to achieve the high peak power density and the high pulse repetition rate. Different shape craters are formed in a patterned structure on the material surface when the laser beam irradiates on it by controlling power density, pulse repetition rate, pulse quantity and pulse interval. In addition, assisting oxygen gas is used for not only improving combustion to deepen the craters but also removing the plasma that generated on the top of craters. Off-focus length classified as negative and positive has a substantial effect on crater diameters. According to the message of rotating angle positions from material to be engraved and the information of graph pixels from computer, a special graph is imparted to the material by integrating the Q- Switched Nd:YAG laser with the computer graph manipulation and the numerically controlled worktable. The crater diameter depends on laser beam divergence and laser focal length. The crater diameter changes from 50 micrometers to 300 micrometers , and the maximum of crater depth reaches one millimeter.

A laser-diode-pumped acoustic-optic Q-switched Nd:YVO4 slab laser with a hybrid resonator

A 32.1 W laser-diode-stack pumped acoustic-optic Q-switched Nd:YVO4 slab laser with hybrid resonator at 1064 nm was demonstrated with the pumping power of 112 W and repetition rate of 40 kHz, the pulse duration was 32.47 ns. The slope efficiency and optical-to-optical efficiency were 37 and 28.7%, respectively. At the repetition rate of 20 kHz and pumping power of 90 W, the average output power and pulse duration were 20.4 W and 20.43 ns, respectively. With the pumping power of 112 W, the beam quality M-2 factors in CW operation were measured to be 1.3 in stable direction and 1.6 in unstable direction.

Upconversion and fluorescence spectral studies of Er3+/Yb3+-codoped Bi(2)Q(3)-GeO2-Ga(2)Q(3)-Na2O glasses

The absorption spectra and upconversion fluorescence spectra of Er3+/-Yb3+-codoped natrium-gallium-germanium-bismuth glasses are measured and investigated. The intense green (533 and 549 nm) and red (672 nm) emission bands were simultaneously observed at room temperature. The quadratic dependence of the green and red emission on excitation power indicates that the two-photon absorption processes occur. The influence of Ga2C3 on upconversion intensity is investigated. The intensity of green emissions increases slowly with increasing Ga2O3 content, while the intensity of red emission increases significantly. The possible upconversion mechanisms for these glasses have also been discussed. The maximum phonon energy of the glasses determined based on the infrared (IR) spectral analysis is as low as 740 cm(-1). The studies indicate that Bi2O3-GeO2-Ga2O3-Na2O glasses may be potential materials for developing upconversion optical devices (c) 2006 Published by Elsevier B.V.