Pulsed pump: Thermal effects in solid state lasers under super-Gaussian pulses

Solid state laser (SSL) powers can be realistically scaled when pumped by a real, efficient and multimode pulse. In this work, a fourth-order super-Gaussian pulse was assumed as a pump for SSL’s and a complete analytical expression for the thermal phase shift is given. Moreover, the focal length of thermal lens in paraxial ray approximation regime was studied. The results when applied to a Ti: sapphire crystal show an appreciable correction for abberation compared to a top-hat pulse.     

Thermal conductivity, dislocation density and GaN device design

The performance of high power transistor devices is intimately connected to the substrate thermal conductivity. In this study, the relationship between thermal conductivity and dislocation density is examined using the 3 omega technique and free standing HVPE GaN substrates. Dislocation density is measured using imaging cathodoluminescence. In a low dislocation density regime below 10⁵ cm⁻², the thermal conductivity appears to plateau out near 230 W/K m and can be altered by the presence of isotopic defects and point defects. For high dislocation densities the thermal conductivity is severely degraded due to phonon scattering from dislocations. These results are applied to the design of homoepitaxially and heteroepitaxially grown HEMT devices and the efficiency of heat extraction and the influence of lateral heat spreading on device performance are compared.     

Multiscale Finite Element Modeling of Arc Dynamics in a DC Plasma Torch

The dynamics of the electric arc inside a direct current non-transferred arc plasma torch are simulated using a three-dimensional, transient, equilibrium model. The fluid and electromagnetic equations are solved numerically in a fully coupled approach by a multiscale finite element method. Simulations of a torch operating with argon and argon–hydrogen under different operating conditions are presented. The model is able to predict the operation of the torch in steady and takeover modes without any further assumption on the reattachment process except for the use of an artificially high electrical conductivity near the electrodes, needed because of the equilibrium assumption. The results obtained indicate that the reattachment process in these operating modes may be driven by the movement of the arc rather than by a breakdown-like process. It is also found that, for a torch operating in these modes and using straight gas injection, the arc will tend to re-attach to the opposite side of its original attachment. This phenomenon seems to be produced by a net angular momentum on the arc due to the imbalance between magnetic and fluid drag forces.     

单个波长到多个波长的变换实验

报道一种波长变换的新方法.采用此方法不需要任何泵浦光便能够直接将信号光变换成在特定谱宽内的任意多个任意波长的变换光,这对于将来的波分复用光网络提供了较大的方便.此波长变换的原理是利用色散位移光纤的非线性效应产生超连续光谱(SC)信号,由于这种SC信号携带有变换光信号,对这种连续谱进行滤波便能够得到所需要的任意频率的变换信号.此变换方式具有变换频带宽,偏振不敏感的优点。     

单层光学薄膜中薄膜－衬底体系的双重干涉效应及其应用

提出了单层光学薄膜中薄膜与衬底反射光之间的双重干涉效应的理论，实验结果证实了理论分析的正确性。双重干涉效应使薄膜－衬底体系的热致反射调制度高达８０％，这一效应可望有极广泛的应用     

Eu^2＋：BaFCl光激励发光过程中紫外线的激发与漂白效应

通过改变紫外线的辐射照能量范围，研究了Ｅｕ＾２＋：ＢａＦＣｌ的光激励发光性质。发现紫外线能量大于Ｅｕ＾２＋的最低激发态能量及紫外线的能量小于Ｅｕ＾２＋最低激发态的能量两种情况下，光激励发光具有明显的差异，分析了产生差异的原因，给出了紫外线的辐照能量发生转时所对应的能级位置。     

A new quantum statistical evaluation method for time correlation functions

Considering a system ofN identical interacting particles, which obey Fermi-Dirac or Bose-Einstein statistics, we derive new formulas for correlation functions of the type (whereB _j is diagonal in the free-particle states) in the thermodynamic limit. Thereby we apply and extend a superoperator formalism, recently developed for the derivation of long-time tails in semiclassical systems. As an illustrative application, the Boltzmann equation value of the time-integrated correlation functionC(t) is derived in a straightforward manner. Due to exchange effects, the obtained t-matrix and the resulting scattering cross section, which occurs in the Boltzmann collision operator, are now functionals of the Fermi-Dirac or Bose-Einstein distribution.     

Surface properties of finite classical Coulomb systems: Debye-Hückel approximation and computer simulations

We report analytical and numerical studies of surface correlations in finite, homogeneously polarizable, classical Coulomb systems placed in an insulating or conducting environment. Their purpose is to understand the phenomenological, shape-dependent laws of electrostatics, from the point of view of statistical mechanics; we focus on the knowledge of the dielectric susceptibility of the system, a quantity proportional to the equilibrium fluctuation of the system's instantaneous polarization per unit volume. This goal has been achieved for a system in a conducting state. The picture is that the shape-dependent part of the susceptibilities results from the action of unbounded observables (the second moments of the instantaneous polarization of the system) on long-range surface correlations and that the relations of electrostatics are verified by means of shape-dependent thermodynamic limits. This picture is supported (i) by exact solutions and asymptotic analysis of the Debye-Hückel approximation of multicomponent plasmas in disks and spheres with insulating and conducting environment and also in ellipses in a vacuum, and (ii) by computer simulations of a one-component plasma in a disk with different environments, notably a conducting environment with permeable and impermeable wall. These observations have revealed for the first time the reason why the susceptibility of a conducting disk in a conductor with impermeable walls diverges linearly with the radius of the disk: this is due to the occurrence of long-range radial correlations in the conductor. These findings are quantitatively interpreted in terms of a novel canonical Debye-Huckel approximation as contrasted to the ordinary grand canonical version. Lastly a fresh look at the problem of the surface correlations of a conductor in a vacuum, which places the observer close to the surface of the conductor but in the vacuum, is presented and applied to the disk, the ellipse, the cylinder, the sphere, and the wedge.     

SiO2与Keggin杂多酸相互作用的研究

采用经典酸化与乙醚萃取相结合的方法，制备了Keggin型杂多酸H3PMo12O40，并以SiO2为载体制备了经不同温度焙烧的负载型杂多酸样品，利用TG、DTA、IR、XPS、NH3－TPD等手段，对负载前后的杂多酸样品进行了表征；考察了SiO2与杂多酸之间的相互作用以及载体对杂多酸酸性的影响，研究发现，SiO2载体的引入，可以有效改善杂多酸的热稳定性，焙烧温度的升高，会显著降低杂多酸的酸性，并提出SiO2杂多酸的相互作用方式。     

分子筛笼内金属羰基簇合物的热稳定性研究

本实验采用戊马比妥钠诱发豚鼠和家兔急性心力衰竭模型，观察了舒心丸的治疗作用。结果表明，舒心丸ｉｖ能明显升高心衰豚鼠的心脏收缩幅度和心衰家兔的Ｂｐ，ＬＶＰ，ＬＶ±ｄｐ／ｄｔ和ＣＯ。其作用与哇巴因相似。