共查询到20条相似文献,搜索用时 78 毫秒
1.
2.
3.
4.
将调Q的Nd:YAG激光脉冲聚焦到FC-72介质池中,利用电荷耦合器件(CCD)和数字图像处理技术,实验研究了后向受激布里渊散射(SBS)光斑的光强分布,获得了其光强分布及光斑大小随入射能量的变化规律。结果表明,在入射光束为基模高斯光束的条件下,随着入射光能量增大,受激布里渊散射光斑的空间光强分布由近高斯型变为高斯型。并且受激布里渊散射光斑大小总体上是随着入射光能量的增大而逐渐减小的。当入射能量在受激布里渊散射阈值附近时,受激布里渊散射光斑大小达到最大(大于入射光斑);当入射能量为3倍阈值以上时,受激布里渊散射光斑大小达到最小(小于入射光斑)。 相似文献
5.
为了研究硅片表面球形粒子的光散射情况,根据Mie氏理论,采用相差模型,得到了球形粒子在任意线偏振光照射下的散射光光强空间分布的计算方法,给出了球形粒子在s偏振和p偏振光分别以0°和70°角照射下散射光微分散射截面的模拟计算结果,并与相关的实验结果进行了比较,对硅片缺陷自动检测仪的研制具有指导意义。 相似文献
6.
光折变晶体全息存储中散射噪声特性的研究 总被引:18,自引:10,他引:8
采用信噪比损失系数 (LSNR)深入研究了光折变铌酸锂晶体中散射噪声对全息输入图像像质的影响。对不同掺杂物质、不同掺杂浓度、不同处理方法以及不同记录方式的大量晶体进行了实验研究 ,并重点考察了物光束引起的散射噪声的特性。实验结果表明 ,氧化态晶体的散射噪声的影响小于生长态和还原态晶体 ,反射光路较之透射光路和邻面入射 ( 90°)光路更不易受散射噪音影响 相似文献
7.
K9玻璃与熔石英玻璃中纵向受激布里渊散射的脉宽压缩和能量提取效率 总被引:1,自引:2,他引:1
以K9玻璃与熔石英玻璃代替传统的液体或气体作为纵向受激布里渊散射(LSBS)样品,波长1.064μm,脉宽12 ns的单纵模电光调QNd∶YAG激光器作抽运光,实验上以脉宽压缩和后向斯托克斯(Stokes)散射光频移为标志,测到后向斯托克斯散射光线宽和散射光脉宽压缩比。研究了纵向受激布里渊散射样品的长度、抽运光能量大小、材料种类对纵向受激布里渊散射脉宽压缩效应和散射光能量提取效率的影响。实验结果表明,熔石英与K9玻璃的受激布里渊散射发生阈值、饱和阈值、散射光能量提取效率、散射光脉冲波形均相近,K9玻璃可以成为一种更廉价的受激布里渊散射介质。针对170 mm的熔石英玻璃样品,找到了纵向受激布里渊散射的发生阈值、饱和阈值,并得到了较高的散射光能量提取效率,从100 mm的熔石英玻璃中获得了87%的散射光能量提取效率,而从170 mm的熔石英中获得了90%左右的散射光能量提取效率。实验数据拟合的规律曲线印证了数值模拟结果。 相似文献
8.
9.
《激光与光电子学进展》2001,(6)
劳伦斯·伯克利国家实验室的研究人员已产生持续不足 30 0 fs的频闪式同步加速器闪光。这些亚皮秒脉冲的光谱范围从红外延伸至 X射线波长。在伯克利实验室的高级光源 ( ALS) ,研究者可直接从同步辐射加速器储存环的电子束中提取飞秒脉冲辐射。从 AL S直线加速器中产生 ( 50 Me V)的相对论电子脉冲与红外激光产生的 10 0 fs脉冲交叉成 90°角。在这种布局中 ,部分红外光子与电子相互作用并被散射。散射光子具有 X射线的能量 ,沿与电子束相同的方向传播 ;离散射脉冲中心最近的光子具有最高的能量。散射脉冲的弛豫时间由红外脉冲通过电子束… 相似文献
10.
11.
《Signal Processing Magazine, IEEE》2002,19(5):37-47
A maximum a posteriori (MAP) estimator using a Markov or a maximum entropy random field model for a prior distribution may be viewed as a minimizer of a variational problem.Using notions from robust statistics, a variational filter referred to as a Huber gradient descent flow is proposed. It is a result of optimizing a Huber functional subject to some noise constraints and takes a hybrid form of a total variation diffusion for large gradient magnitudes and of a linear diffusion for small gradient magnitudes. Using the gained insight, and as a further extension, we propose an information-theoretic gradient descent flow which is a result of minimizing a functional that is a hybrid between a negentropy variational integral and a total variation. Illustrating examples demonstrate a much improved performance of the approach in the presence of Gaussian and heavy tailed noise. In this article, we present a variational approach to MAP estimation with a more qualitative and tutorial emphasis. The key idea behind this approach is to use geometric insight in helping construct regularizing functionals and avoiding a subjective choice of a prior in MAP estimation. Using tools from robust statistics and information theory, we show that we can extend this strategy and develop two gradient descent flows for image denoising with a demonstrated performance. 相似文献
12.
Yanagawa H. Ochiai T. Hayakawa H. Miyazawa H. 《Lightwave Technology, Journal of》1989,7(11):1646-1653
A design in which a filter is embedded in a fiber fixed on a substrate is proposed. It was successfully applied to the fabrication of low loss fiber optic components for a single-mode fiber transmission system. These components have a wide operational temperature range. The design is easily adapted to a multifilter or multifiber component. Filter embedding is achieved in two ways. One is to insert a thin filter chip in a slit which is machined into a fiber fixed on a substrate by a dicing saw (filter inserted type). The other is to evaporate a filter film directly on a fiber end face and butt this fiber to another fiber on a guide groove on a substrate (filter evaporated type) 相似文献
13.
《Microwave Theory and Techniques》1961,9(2):201-202
The purpose of this note is to present an alternate derivation of a formula for the synthesis of a loaded line. The problem is to determine the values of the normalized susceptances a and c mounted an exact quarter-wavelength apart along a uniform line. These are arranged in the order a, c, c,. . .c, a to achieve a loaded line with a given phase shift and perfect match. In order to analyze a particular line design for standing-wave ratio and phase shift over a band of frequencies on a digital computer, it is worthwhile to know the values of the susceptances to many more decimal places than one would achieve from a simple graph. 相似文献
14.
A wireless mesh network is a wired extension of a multihop ad hoc network that defines a new paradigm for broadband wireless Internet access. A packet originating from a mesh client is relayed collaboratively in a multihop fashion by the intermediate mesh routers toward an Internet gateway. All existing mesh routing protocols assume that each MR honestly participates in packet forwarding. This is valid only in a network managed by a single trusted authority. However, a community-based WMN can be formed by a group of independent MRs operated by different service providers. It is a real challenge to establish a priori trust in a multi-operator WMN. In such a situation, a selfish MR might be motivated to monopolize the wireless channel for itself by intentionally dropping others? packets. This results in severe performance degradation. Thus, enforcing collaboration is a determinant aspect in designing a secure and reliable WMN. In this article we analyze selfishness of MRs in a multi-operator WMN and explore its overall negative impact on network performance. We finally present a summary of various existing schemes with respect to detecting selfishness, analyze their usefulness in WMNs, and highlight their relative advantages and deficiencies. 相似文献
15.
《IEEE transactions on information theory / Professional Technical Group on Information Theory》1965,11(4):544-549
Alterations in probability densities produced by iterative application of Bayes' rule are analyzed. Computational requirements for finding a sequence of a posteriori densities remain reasonable despite a growing sample size if and only if a sufficient statistic expressible as a vector of fixed dimension exists. The existence of such a sufficient statistic also insures existence of reproducing a priori probability densities (a priori probability densities insuring that the a posteriori densities are in the same family). The theory is applied to find a class of sequential Bayes estimators for a Gaussian covariance matrix, and to treat a variety of adaptive "Bayesian learning" schemes in a unified manner. 相似文献
16.
Avitabile G.F. Maci S. Biffi Gentili G. Roselli L. Manes G.F. 《Electronics letters》1992,28(25):2277-2279
A multilayer structure, based on a patch antenna coupled through a nonresonant slot to a pair of feeding microstrips is a versatile module which can be used as a radiating and resonating element in a number of different configurations. Direct connection to a low cost transistor in a feedback loop results in a very simple active antenna, as reported. Different termination conditions at the four microstrip ports give rise to a number of alternative configurations for active generation/detection and multipatch arrays.<> 相似文献
17.
介绍一种用MCS-51单片机控制的PTCR热敏电阻器阻-温特性测试系统,其中分压取样电阻器采用模拟开关进行切换。测试系统由样品室、模拟开关、R-V变换器、信号放大器、A/D转换器、D/A转换器、记录仪、单片机和打印机等部分组成,样品室内设有加热电炉和热电偶等部件。 相似文献
18.
Namiki A. Komuro T. Ishikawa M. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》2002,90(7):1178-1187
This paper discusses a design concept of a sensory-motor fusion system to achieve high performance in a dynamic changing environment. From the viewpoint of a dynamic system, the new concept called "dynamics matching" is proposed to match the dynamics constraints of a system. Based on this concept, we describe a high-speed vision chip that has a general purpose parallel processing array along with a photodetector all in a single silicon chip. Next we describe a new sensory-motor fusion system which consists of a hierarchical parallel processing system, a vision chip system, and a multifingered hand-arm. All sensory feedback, including visual feedback, can be achieved in 1 ms. In addition, as an application of the system, we demonstrate high-speed grasping using visual and force feedback. 相似文献
19.
《Electron Devices, IEEE Transactions on》1969,16(11):923-927
A computer-aided design of a Si avalanche photodiode is presented. As an example, the design of the boron diffused photodiode with a desired time constant is carried out. The choice of an area of an active region is not affected by a diffusion condition but primarily by a substrate impurity concentration. For a very high speed response a moderate substrate impurity concentration must be selected. For a longer time constant than about 0.1 ns an increasing area of an active region is acceptable with a decreasing substrate impurity concentration. In a lightly doped substrate, a uniform multiplication of an active region cannot occur. Using the usual diffusion technique the acceptable highest resistivity of a substrate is about 1-2 Ω.cm. The capacitance of the guard ring occupies a considerable part in a total capacitance. Calculated results are in good agreement with experimental results. 相似文献
20.
Le Jian Wang Cao Yang Jintao Zhang Hao Li Xingrui 《International Journal of Electronics》2018,105(11):1881-1899
A dynamic voltage restorer (DVR) can be installed in a middle-voltage (MV) power grid, to concurrently protect a cluster of sensitive loads from voltage sags. To further improve its efficiency and reduce the difficulty in its implementation, a novel control strategy for operating such a DVR as a virtual impedance in series with sensitive loads is proposed in this paper. In addition to its usual function of compensating for voltage sags, such a DVR can also operate as a virtual inductance, to function as a fault current limiter (FCL) during a downstream fault, or a virtual capacitance, to function as a series compensator (SC) to compensate the voltage loss along the feeder line during heavy load. Based on a dual-loop control design, strategies for operating a DVR as a series virtual inductance and a virtual capacitance are proposed, and methods for tuning the parameter values and a stability analysis of the whole system are presented. The feasibility and effectiveness of the proposed method are verified by simulations using the PSCAD software, and experimental results obtained using a prototype DVR are presented. 相似文献