激光玻璃与包边玻璃的折射率匹配

从理论上详细探讨了基质激光玻璃与包边玻璃的折射率匹配与剩余反射率的关系,并从实验上验证了折射率匹配越好,吸收系数与包边玻璃厚度的乘积越大,则剩余反射率越低,从而对激光放大器中寄生振荡的抑制越好,增益也就越高。

Effects of CO2 laser conditioning of the antireflection Y2O3/SiO2 coatings at 351 nm

Y2O3/SiO2 coatings were deposited on fused silica by electron beam evaporation. A continuous wave CO2 laser was used to condition parts of the prepared samples at different scanning speeds in the air. LAMBDA 900 spectrometer was used to investigate the changes of the transmittance and residual reflection spectrum. A Nomarski microscope under dark field was used to examine the changes of the micro defect density. The changes of the surface roughness and the microstructure of the film before and after conditioning were investigated by AFM and X-ray diffraction, respectively. We found that laser-induced damage threshold (LIDT) of the films conditioning at 30 mm/s scanning speed was increased by more than a factor of 3 over the thresholds of the as-deposited films. The conditioning effect was correlated with an irradiation-induced decrease of the defect density and absorption of the films. (c) 2005 Elsevier B.V. All rights reserved.

SiO_2薄膜折射率的准确拟合分析

精确的光学常数对于设计和制备高品质的光学薄膜非常重要,尤其是那些光学性能对折射率变化敏感的薄膜。SiO_2是一种常用的低折射率材料,因与常用基底折射率相近使其准确拟合有一定难度。实验通过离子束溅射制备了SiO_2单层膜。考虑测量时的误差和基底折射率的影响,采用透射率包络和反射率包络得到了SiO_2的折射率,并用所得折射率进行反演来对这两种途径在实际测量拟合过程中的准确性进行比对。分析表明,剩余反射率在实际的测量过程中误差更小,直接用测量镀膜前后基片的剩余反射率值可以更简便更准确地得到SiO_2的折射率,能达到10~(-2)的精度。

A V-shaped module technique for promoting generation photocurrent density of silicon solar cells

A V-shaped solar cell module consists of two tilted mono-crystalline cells [J. Li, China Patent No. 200410007708.6 (March, 2004)]. The angle included between the two tilted cells is 90 degrees. The two cells were fabricated by using polished silicon wafers. The scheme of both-side polished wafers has been proposed to reduce optical loss. Compared to solar cells in a planar way, the V-shaped structure enhances external quantum efficiency and leads to an increase of 15% in generation photocurrent density. The following three kinds of trapped photons are suggested to contribute to the increase: (1) infrared photons converted from visible photons due to a transformation mechanism, (2) photons reflected from top contact metal, and (3) a residual reflection which can not be eliminated by an antireflection coating.

FEM Simulations and Optimization about Residual Stresses in Coating Structures with Functionally Graded Materials Layer

An elasto-plastic finite element method is developed to predict the residual stresses of thermal spraying coatings with functionally graded material layer. In numerical simulations, temperature sensitivity of various material constants is included and mix

Interferometric Measurement of Density in Nonstationary Shock Wave Reflection Flow and Comparison with CFD

We present density measurements from the application of interferometry and Fourier transform fringe analysis to the problem of nonstationary shock wave reflection over a semicircular cylinder and compare our experimental measurements to theoretical results from a CFD simulation of the same problem. The experimental results demonstrate our ability to resolve detailed structure in this complex shock wave reflection problem, allowing visualization of multiple shocks in the vicinity of the triple point, plus visualization of the shear layer and an associated vortical structure. Comparison between CFD and experiment show significant discrepancies with experiment producing a double Mach Reflection when CFD predicts a transitional Mach reflection.

Numerical Simulation of Transient Thermal Field and Residual Stress in Laser Melting Process

以激光熔凝表面强韧化处理为背景,应用空间弹塑性有限单元和高精度数值算法同时考虑材料组织性能的变化模拟工件的温度场及残余应力,研究激光熔凝加工中瞬时温度场及残余应力数值模拟,同时考虑相变潜热及相变塑性的影响,用算例验证了模型的正确性,给出了不同时刻温度场分布及残余应力分布。

Thermal Residual Stresses in Particulate Composites and Its Toughening Effect

In this paper, an accurate formula for calculating the thermal residual stress field in a particle-reinforced composite are presented. Numerical examples are given to show r-variations of the thermal residual stresses. The increase in fracture toughness of matrix predicted by the thermal residual stress field is compared well with the experimentally measured increase.

Analysis of residual stress gradient in MEMS multi-layer structure

Residual stress and its gradient through the thickness are among the most important properties of as-deposited films. Recently, a new mechanism based on a revised Thomas-Fermi-Dirac (TFD) model was proposed for the origin of intrinsic stress in solid film

Biosensor with Total Internal reflection Imaging Ellipsometry

In order to monitor multiple protein reaction processes simultaneously, a biosensor based on imaging ellipsometry operated in the total internal reflection mode is proposed. It could be realised as an automatic analysis for protein interaction processes with real-time label-free method. Its principle and methodology as well as a demonstration for its applications are presented.

An Effective Method of Determining the Residual Stress Gradients in a Micro-Cantilever

A method of determining the micro-cantilever residual stress gradients by studying its deflection and curvature is presented. The stress gradients contribute to both axial load and bending moment, which, in prebuckling regime, cause the structural stiffness change and curving up/down, respectively. As the axial load corresponds to the even polynomial terms of stress gradients and bending moment corresponds to the odd polynomial terms, the deflection itself is not enough to determine the axial load and bending moment. Curvature together with the deflection can uniquely determine these two parameters. Both linear analysis and nonlinear analysis of micro-cantilever deflection under axial load and bending moment are presented. Because of the stiffening effect due to the nonlinearity of (large) deformation, the difference between linear and nonlinear analyses enlarges as the micro-cantilever deflection increases. The model developed in this paper determines the resultant axial load and bending moment due to the stress gradients. Under proper assumptions, the stress gradients profile is obtained through the resultant axial load and bending moment.

Scheme Construction with Numerical Flux Residual Correction (NFRC) and Group Velocity Control (GVC)

For simulating multi-scale complex flow fields like turbulent flows, the high order accurate schemes are preferred. In this paper, a scheme construction with numerical flux residual correction (NFRC) is presented. Any order accurate difference approximation can be obtained with the NFRC. To improve the resolution of the shock, the constructed schemes are modified with group velocity control (GVC) and weighted group velocity control (WGVC). The method of scheme construction is simple, and it is used to solve practical problems.

The Mach reflection of a detonation based on soot track measurements

This paper presents a series of soot tracks formed by gaseous detonation waves diffracting around wedges with different wedge angles. These cellular structure patterns describe the Mach-reflection processes of a detonation and reveal some unique characteristics. They can be used to analyze the relationship between the trajectory angle of the triple point, wedge angle, and initial pressure in Mach reflection. Compared to the Mach-reflected one-dimensional shock wave in nonreactive air, all these unique characteristics for a Mach-reflected detonation should be attributed to the transverse-wave structure of the detonation front; meanwhile, the precursor shock wave and transverse wave influence the Mach-reflected detonation, respectively. The experimental results support the recently published numerical simulation of this complex phenomenon.

Wave Dynamic Processes in Cellular Detonation Reflection from Wedges

When the cell width of the incident detonation wave (IDW) is comparable to or larger than the Mach stem height, self-similarity will fail during IDW reflection from a wedge surface. In this paper, the detonation reflection from wedges is investigated for the wave dynamic processes occurring in the wave front, including transverse shock motion and detonation cell variations behind the Mach stem. A detailed reaction model is implemented to simulate two-dimensional cellular detonations in stoichiometric mixtures of H (2)/O (2) diluted by Argon. The numerical results show that the transverse waves, which cross the triple point trajectory of Mach reflection, travel along the Mach stem and reflect back from the wedge surface, control the size of the cells in the region swept by the Mach stem. It is the energy carried by these transverse waves that sustains the triple-wave-collision with a higher frequency within the over-driven Mach stem. In some cases, local wave dynamic processes and wave structures play a dominant role in determining the pattern of cellular record, leading to the fact that the cellular patterns after the Mach stem exhibit some peculiar modes.

Ocean Waves Propagating over a Porous Seabed: Residual and Oscillatory Mechanisms

Two mechanisms for the wave-induced pore pressures in a porous seabed, i.e. oscillatory and residual excess pore pressures, have been observed in laboratory experiments and field measurements. Most previous investigations have focused on one of the mechanisms individually. In this paper, an analytical solution for the wave-induced residual pore pressure, which is not available yet, is derived, and compared with the existing experimental data. With the new solution, a parametric analysis is performed to clarify the applicable ranges of two mechanisms. Then, a simplified approximation for the prediction of wave-induced liquefaction potential is proposed for engineering practice.