激光熔覆铁基大厚度非晶合金表层的研究

利用激光熔覆制备了大厚度铁基非晶合金表层，非晶层厚度为0.74mm，表征非晶合金过冷液相区的ΔT(非晶转变温度及晶化温度之差)为67K。XRD、TEM与DSC分析表明表层为单相非晶。分析了非晶形成机制。

Direct Numerical Simulation of Supersonic Turbulent Boundary Layer Flow

Direct numerical simulations of a spatially evolving supersonic flat-plate turbulent boundary layer flow with free Mach number M = 2.25 and Reynolds number Re = 365000/in are performed. The transition process from laminar to turbulent flow is obtained by solving the three-dimensional compressible Navier-Stokes, equations, using high-order accurate difference schemes. The obtained statistical results agree well with the experimental and theoretical data. From the numerical results it can be seen that the transition process under the considered conditions is the process which skips the Tolimien-Schlichting instability and the second instability through the instability of high gradient shear layer and becomes of laminar flow breakdown. This means that the transition process is a bypass-type transition process. The spanwise asymmetry of the disturbance locally upstream imposed is important to induce the bypass-type transition. Furthermore, with increasing the time disturbance frequency the transition will delay. When the time disturbance frequency is large enough, the transition will disappear.

空潜信道中基于多光束阵列的二维图案传输

提出了一种利用多光束阵列在复杂散射信道中进行二维图案传输的理论模型。与传统多光束传输方案思路不同，该模型有效利用信道的强散射特性，使各光束充分扩散，在接收面形成交迭区域，成像光学系统在该区域内接收光信号并恢复各发射光束的空间位置信息，完成二维图案信息在空潜信道中的多通道传输。视在参数的引入使光束原本在两个不同折射率介质中的传输简化为仅在一种介质中传输的简单问题。实验采用直径为15mm的微透镜阵列以及长为12．65m的海水、大气信道来模拟实际信道中的强散射作用，结果表明该模型具有较好的可行性。

Hit-or-miss representation of a pattern spectrum and its optical implementation

We demonstrate that a pattern spectrum can be decomposed into the union of hit-or-miss transforms with respect to a series of structure-element pairs. Moreover we use a Boolean-logic function to express the pattern spectrum and show that the Boolean-logic representation of a pattern spectrum is composed of hit-or-miss min terms. The optical implementation of a pattern spectrum is based on an incoherent optical correlator with a feedback operation. (C) 1996 Optical Society of America

基于基频分量消光的1/4波片快轴标定方法

提出了一种基于基频分量消光的波片快轴标定方法,并利用琼斯矩阵对其标定原理进行了分析。激光器、起偏器、相位调制器、待标定1/4波片、检偏器和光电探测器构成标定光路,起偏器、检偏器的透光轴与相位调制器的振动轴分别成+45°和0°夹角。准直激光束依次经过起偏器、相位调制器、待标定1/4波片和检偏器,由光电探测器接收。理论分析表明该标定方法标定精度主要取决于检偏器的定位误差。实验验证了该标定方法的有效性,1/4波片快轴标定结果的最大偏差为0.043°,标准差为0.012°,标定精度为0.05°。

Polarizing beam splitter of deep-etched triangular-groove fused-silica gratings

We investigated the use of a deep-etched fused-silica grating with triangular-shaped grooves as a highly efficient polarizing beam splitter (PBS). A triangular-groove PBS grating is designed at a wavelength of 1550 nm to be used in optical communication. When it is illuminated in Littrow mounting, the transmitted TE- and TM-polarized waves are mainly diffracted in the minus-first and zeroth orders, respectively. The design condition is based on the average differences of the grating mode indices, which is verified by using rigorous coupled-wave analysis. The designed PBS grating is highly efficient over the C+L band range for both TE and TM polarizations (> 97.68 %). It is shown that such a triangular-groove PBS grating can exhibit a higher diffraction efficiency, a larger extinction ratio, and less reflection loss than the binary-phase fused-silica PBS grating. (C) 2008 Optical Society of America.

激光脉冲宽度对有质动力加速电子的影响

基于真空中单电子运动模型，编程计算得到了高斯激光脉冲与初始位于激光传播轴上电子的相互作用结果。不同激光参鼍条件下，得到了电子的能量增益与激光强度、焦斑大小和脉冲宽度关系。结果表明，高斯激光脉冲焦斑较大时，电子没有明显的能量增益，高斯激光脉冲焦斑太小时，电子也没有明显的能量增益。电子的能量增益有一个最佳焦斑大小。在相同激光强度下，电子能量增益的最佳焦斑大小随脉冲宽度的增大而增大，但最佳焦斑大小与脉冲宽度的比值基本上是不变的。

Influences of radiation trapping on spectroscopic properties of Er3+-doped fluorophosphate glasses

Fluorophosphate glasses with different contents of ErF3 were prepared. Due to the radiation trapping of Er, concentration dependence of the fluorescence lifetime is subject to distortion, and the stimulated-emission cross section calculated by the Fuchtbauer-Ladenburg equation is underestimated. The influence of radiation trapping on the measured fluorescence lifetime and width are investigated quantitatively. By comparing the intensity ratio of the 1556-1532 nm peak in the fluorescence spectrum with that in the stimulated-emission cross-section spectrum obtained according to the McCumber theory, the distortion ratio of fluorescence spectrum due to radiation trapping is obtained. An empirical way to quantitatively evaluate the influences of radiation trapping on fluorescence lifetime and width is proposed. (c) 2007 Optical Society of America.