Numerical Simulation of SRS of Cylindrical Wave Beams

A method for numerical simulation of stimulated Raman scattering of cylindrical wave beams in a nonlinear medium has been developed. The features of the spatial structure formation of interacting wave fields in the regime of conservation of azimuthal angular distributions of amplitudes have been investigated. The radial intensity profiles of diffracting light beams in the near-field zone and their angular spectra in the far-field zone corresponding to different stages of energy exchange in the process of amplification from the noise in the barium nitrate crystal have been calculated. It has been shown that in the field of Bessel beams waveguide structures of the soliton type with a peak intensity of the self-channeling Stokes component significantly exceeding the initial pumping intensity are formed. A comparison of the conversion efficiencies under pumping by Gaussian and Bessel light beams has been made.     

Gaussian Fields and Random Packing

Consider sequential packing of unit volume balls in a large cube, in any dimension and with Poisson input. We show after suitable rescaling that the spatial distribution of packed balls tends to that of a Gaussian field in the thermodynamic limit. The results cover related applied models, including ballistic deposition and spatial birth-growth models.     

三维空间管道的重建与分析

本文在假设切片最大内含圆半径即为滚动球半径的前提下 ,通过在每一切片中寻找最大内含圆所有可能的圆心 ,并用邻近层切片信息对所有可能圆心进行筛选 ,比较准确地定出了 0～ 99层的中轴线坐标 ;外推了 1 0 0～ 1 2 8层、-1～ -2 9层的中轴线坐标 ;用所求中轴线坐标重建切片并与原切片比较 ,相异象素点个数相对误差不超过 0 .5 % .     

多周期双啁啾镜结构的空间解波分复用器

以穿透深度依赖于入射波长的基本双啁啾结构为基础，通过对其中的布拉格膜对进行“周期 重复”的方法来提高空间线性侧向位移，从而实现不同波长的入射光的空间分离，用于高集成度的薄膜空间解波分复用器件的设计.比较了总层数相同的直接双啁啾结构和重复周期为n倍的改进结构，发现后者在理论设计更具有应用优势，同时在实验制作上有更高的容差性 .对空间色散特性曲线在周期重复数较大、入射波长较大的情况下所出现的强烈振荡做出了定性分析. 关键词： 双啁啾结构 空间色散 波分复用 薄膜器件     

REE示踪研究坡面侵蚀时空演变过程

在室内人工模拟降雨条件下, 通过沿坡面垂直分段和分层结合布设不同的稀土元素, 研究坡面侵蚀的时空演变规律. 结果表明: 次降雨条件下在产流开始20 min内, 坡面片蚀和细沟侵蚀的平均侵蚀加速度、平均侵蚀率和累积侵蚀量之比分别为1:1, 1:1.5和1:1.3, 坡面下1/3区域的平均侵蚀加速度、平均侵蚀率和累积侵蚀量分别是坡面中部的5, 12, 13倍; 后期细沟平均侵蚀加速度、平均侵蚀率和累积侵蚀量分别为片蚀的43, 7, 5倍. 连续小雨强降雨条件下, 产流35 min内, 细沟侵蚀平均加速度是片蚀的7～10倍, 35 min后, 坡面处于稳定状态; 降雨产流10 min内, 坡面下1/3区域平均侵蚀加速度是坡面中部的5倍, 沟头激活后, 坡面中部的平均侵蚀加速度达到坡面下1/3区域的4倍; 坡顶部存在一个相对稳定区. 说明REE示踪技术能够同时量化随时间和空间变化的坡面侵蚀过程.     

Transmission Fluctuation Spectrometry with Spatial Correlation

Transmission fluctuation spectrometry (TFS) is being developed as a new method of particle size analysis. In the early approaches, the particle suspension was illuminated by one beam with finite beam diameter and the transmission signals underwent a process with variable spatial and/or temporal averaging and a subsequent nonlinear operation. The transmission fluctuations were obtained as a spectrum which included the information on particle size distribution and particle concentration. A new approach presented here employs two narrow parallel beams. While changing the beam separation, the transmission fluctuations of these two beams are expressed in terms of the expectancy of the transmission product (ETP). The analytical expression of the ETP through a monolayer is derived and the ETP of a 3‐dimensional suspension is formulated based on the layer model. The deviation between the transition functions of 3‐dimensional suspensions and monolayers is found to be affected by effects from particle overlapping and monolayer structure.     

Observation of out-coupling of a nematicon

In this work we present the observation of spatial optical solitons in liquid crystal cells by recording the diffraction pattern of the out-coupled beam on a distant screen. Simultaneously, the light propagation is observed via scattering measurements. The most important observation is displacement of the beam on the screen due to the transverse undulation inside the cell. This undulation is caused by the anisotropic walk-off of the beam. The displacement is in good agreement with the values of the undulation earlier reported.     

Spatial distribution of SiCln （n=O-2） in SICl4 plasma measured by mass spectroscopy

For a better understanding of the deposition mechanism of thin films in SiCl4 source gas, we have measured the spatial distributions of SiCln （n=0-2） radicals in SICl4 radio frequency glow discharge plasma utilizing a mass spectrometer equipped with a movable gas sampling apparatus. The experimental results demonstrate that the relative densities of SiCln （n=0-2） radicals have peak values at the position of 10 mm above the powered electrode along the axial direction; the relative densities of the Si and SiCIn （n=1, 2） radicals have peak values at the positions of 27mm and 7 mm away from the axis along the radial direction, respectively. Generally speaking, in the whole SICl4 plasma bulk region, the relative density of Si is one order of magnitude higher than that of SICl, and the relative density of SiCl is several times higher than that of SICl2. This reveals that Si and SiCl may be the primary growth precursors in forming thin films.     

空间差分格式对有限体积法数值散射的影响

数值散射是辐射传递方程近似算法中最常见的离散误差。本文主要讨论空间差分格式对有限体积法数值散射的影响。构造激光平行及倾斜入射的物理模型,验证和比较阶梯格式、中心差分格式及指数格式下温度场的计算精度及数值散射特性。计算结果表明,在激光平行入射与倾斜入射两种情况下,阶梯格式引起的的数值散射比菱形格式及指数格式要多,但其计算精度高于菱形及指数格式。不同激光入射条件下,各种差分格式表现出的数值散射分布有明显的差异。     

三维测量中空间编码技术的研究

针对三维测量中的关键技术——空间编码技术，介绍了空间编码技术对测量的精度、速度和可靠性方面所起的重要作用。阐述了基于三角法结构光投影的测量原理。对空间编码技术在三维测量中的功能进行了研究，介绍了编码原理，总结了编码方案所应满足的条件。列举了当前典型的几种编码方案和一种新的条纹边界编码方案，并对它们进行了分析和比较，指出了它们各自的优缺点和发展趋势。在此研究基础上对空间编码技术作了进一步的总结，指出该领域未来的发展方向将是彩色编码与已有编码的结合。