Fresnel Diffraction Images of Periodic Objects under Gaussian Beam Illumination

The Fresnel diffraction field of plane periodic objects under single TEM 00 mode gaussian beam illumination is studied. Use of the Fresnel-Kirchhoff diffraction formula allows the axial localization and lateral magnification, the basic parameters of the diffraction images, to be determined. The analysed self-imaging phenomenon and the case of uniform beam illumination are compared and discussed.     

Theory and Applications of Dynamic Laser Speckles Due to In-plane Object Motion

The dynamic behaviour of laser speckle caused by uniform in-plane motion of a diffuse object has been studied by deriving the cross-correlation functions of the complex disturbance and the intensity in a field where the speckle is observed. The expressions for the diffraction and the image fields are calculated from general formulae for a linear coherent system. On the basis of these functions two characters in the dynamic behaviour of speckle, a bodily translation and a gradual change in structure, are discussed quantitatively. The velocity of the translation and the rate of the structure change have been derived. As applications of the relations obtained several new methods have been proposed for measuring pattern correlations, MTF of imaging systems, in-plane velocity of diffuse objects, and eye accommodation state.     

Contrast Enhancement of Gaussian Speckles Produced by Centrosymmetrical Objects

Abstract

It is well known that the contrast of Gaussian speckles produced under ordinary optical configurations is at most 1. It is also known, however, that under some special situations even Gaussian speckles can have contrast values higher than 1. As an example of such a situation, this paper discusses the first-order statistics of speckle patterns produced in the Fraunhofer region of objects having centrosymmetrical structures. The first-order statistics of Gaussian speckles is first reviewed with special emphasis on the optical conditions which produce the contrast enhancement. Enhanced contrast and the intensity distributions which deviate from the negative exponential density are elucidated theoretically in the case of speckles produced by random objects containing centrosymmetrical structures. Some experimental verifications are also given for the speckle patterns produced by randomly distributed circular apertures containing some symmetrical pairs.     

梁在动荷载作用下若干参数的测试技术研究

应用应变片电阻应变测量的方法研究了简支梁和悬臂梁在动荷载的作用下的若干动态参数,包括动荷系数,固有频率,阻尼系数等。详细叙述了用应变片电阻应变测量技术测定简支梁和悬臂梁的参数的过程以及数据处理的方法;并对所测定的简支梁和悬臂梁的动态参数的准确性进行讨论,指出方案中的优点和不足。     

基于动态背景下的海上运动目标检测

针对目前传统的运动目标检测算法基本上仅适用于静态背景下,对于背景不固定的的场合,传统的目标检测算法检测到的效果不理想问题,提出一种改进的四帧差分法与背景减除法相结合的融合算法。该算法结合传统的运动目标检测算法的特点,能够在动态背景下对海上运动目标进行有效地检测,然后通过提取运动目标的区域轮廓和利用区域的形状描述子将海上运动目标标记出来,为进行后续的运动目标跟踪或匹配创造条件。最后,通过对现场采集的视频序列进行检测,验证了该算法的有效性以及较强的适应性。     

基于简谐激励下响应的梁损伤识别

采用扭转弹簧模拟悬臂梁的损伤,导出了损伤悬臂梁位移模态、转角模态的近似公式,获得了损伤悬臂梁在单点简谐激励下,零初始条件时的位移响应和转角响应.发现损伤悬臂梁的转角响应在损伤处发生阶跃变化,损伤悬臂梁的转角响应对位置的一阶偏导数在损伤处发生脉冲函数型突变的特点,从而提出了基于损伤梁转角响应的损伤判据函数.数值仿真算例表明,所提出的判据函数可以判别损伤的位置和损伤的程度.     

动态图像的拼接与运动目标检测方法的研究

动态图像运动目标检测是图像处理中的热点,但动态图像的识别范围却成了目标检测的限制,针对此问题,本文提出了一种利用图像拼接技术扩展图像识别范围、并在此基础上完成运动目标检测的方法。在图像拼接中采用了SURF图像匹配算法,运动目标识别利用背景差分法,实验中使用的是开源的Linux操作系统、以及为图像处理提供了大量算法和函数的Open CV软件开发库。针对不同分辨率、不同角度采集的图像进行了实验研究,结果表明,可以在较好满足图像识别范围的同时,明确地检测出运动目标的相关信息。同时,本文提出一种通过图像拼接实现扩展运动目标检测的方法,满足了实时性要求,达到了增加图像清晰度的目的,但是,在摄像设备与场景之间的相对运动方面还存在着有待解决的问题,这将成为今后研究的重点方向。     

Focusing Properties of the Gaussian Beam Generated by Optical Resonators with Gaussian Reflectivity Mirrors

Abstract

This paper presents a parametric study concerning the focusing properties of the light beam generated by optical resonators with Gaussian reflectivity mirrors. The diffraction integral has been evaluated and analytical expressions are derived for intensity patterns near the focus in systems of different Fresnel numbers. Universal curves have been plotted against dimensionless parameters to show the variations in the intensity patterns due to the change in focusing geometry and the incident beam intensity profile. Modification to the well known diffraction formula are considered in order to extend the conventional Gaussian formalism to the case of Gaussian mirror resonators.     

高斯光束均束器光学系统设计

为了提高激光光束的应用水平,需要将高斯光束整形为平顶光束。分析了非球面高斯光束均束器的基本原理和设计理论,选用超高斯光束函数作为平顶光束的数学-物理模型,建立了入射高斯光束与出射平顶光束之间的映射关系式,给出了高阶非球面的面型参数,利用光学设计软件ZEMAX设计了高斯光束均束器光学系统。系统入射光束直径为2 mm,出射光束直径为4 mm,激光波长为1064 nm。分析了能量转换效率,根据Bessel公式定义了平顶光束的平顶度。设计结果实现了激光束的2倍准直扩束、95.98%的能量转换效率和96.6%的平顶度。     

基于时域响应的强耦合梁损伤检测

应用有限元法将连续梁结构简化为两跨强耦合的欧拉-伯努利梁模型,利用直接积分法求出系统在外激励如冲击荷载作用下的动态响应,并进一步推导出动态响应对物理参数(如杨氏模量)的灵敏度.在反问题中,利用基于时域响应的有限元模型修正法进行了强耦合梁系统局部损伤的识别,讨论了人工测量噪声对损伤识别结果的影响.算例表明所提能够快速有效地检测出强耦合梁的局部损伤,并具有高精度,对测量噪声不敏感等特点.     

Dynamic Properties of Laser Speckles on Images Transmitted Through an Image Fibre-bundle

Abstract

The statistical properties of time-varying laser speckles appearing on an image transmitted through an image fibre-bundle are studied experimentally and theoretically. The effect of defocusing on a stage of observation is investigated in relation to the stationarity of the detected speckle intensity. It is shown that a large amount of defocusing produces a stationary speckle field for which the correlation function of the speckle intensity variation is obtained in a stable form. This allows a system for monitoring the velocity of moving objects using an image fibre-bundle to be developed.     

胶体中布朗粒子简谐束缚下准直高斯光束的动态光散射

在将散射粒子间的相互作用看作简谐力、入射光为准直高斯光束、散射光为理想平面光波的模型下研究了胶体溶液中布朗粒子的统计特征并求解了动态光散射的散射光电场强度的自相关函数；     

环形孔径高斯光束的远场特性

讨论环形孔径高斯光束的远场光斑能量分布，并给出拟合表达式。首先推导光束没有抖动时远场光斑的光能分布表达式，然后研究各种不同中心遮拦和不同光束截断比，在有以及没有激光束抖动的情况下，对高斯光束的远场环围能量分布变化的影响。     

基于卡尔曼滤波的运动目标速度测量

移动机器人和智能无人驾驶车辆实时测量运动目标速度是实现自主导航的关键问题。提出了基于Kinect摄像机的机器视觉测速方法,利用图像处理技术检测运动目标,使用速度计算公式获取运动目标速度观测值。为提高速度测量精确度,减少环境噪声影响,应用卡尔曼滤波算法估计运动目标速度。试验结果表明,该方法在移动机器人作任意形式运动过程中可以实时方便地测量运动目标的直线速度以及角速度,具有高精确性、稳定性和广泛应用性。     

Determination of the Coordinates of the Center of a Gaussian Beam by Means of a Matrix Photodetector Using a Weighting Method

A weighting algorithm to determine the coordinates of the center of a Gaussian laser beam projected onto a matrix photodetector is considered. The influence of the internal noise of the photodetector, the maximum brightness of the signal at the beam maximum, and the beam radius on the precision of the algorithm is investigated. Recommendations on image processing are presented.     

基于引信炮口磁探测的单线圈被动测速原理

现有的炮口实时测速都是通过改造发射系统和火控系统完成的,存在成本高,改造技术复杂和存在交联电路等诸多弊端.针对这些问题,提出了一种新的弹上被动测速方法.在分析弹丸运动、磁感应强度变化和单线圈传感器输出信号关系的基础上,提出通过捕获弹丸开始加速和出炮口时线圈输出的两个信号,来实现被动测速的原理,阐述了单线圈被动测速需要考虑的线圈设计、测试误差分析、盲区问题、信号处理以及装定对测速的影响等工程技术问题,列举了单线圈测速的若干优点,指出了需要进一步探讨和研究的问题.     

Gaussian Process Modeling Using the Principle of Superposition

Partial differential equation (PDE) models of physical systems with initial and boundary conditions are often solved numerically via a computer code called the simulator. To study the dependence of the solution on a functional input, the input is expressed as a linear combination of a finite number of basis functions, and the coefficients of the bases are varied. In such studies, Gaussian process (GP) emulators can be constructed to reduce the amount of simulations required from time-consuming simulators. For linear initial-boundary value problems (IBVPs) with functional inputs as additive terms in the PDE, initial conditions, or boundary conditions, the IBVP solution is theoretically a linear function of the coefficients conditional on all other inputs, which is a result called the principle of superposition. Since numerical errors cause deviation from linearity and nonlinear IBVPs are widely solved in practice, we generalize the result to account for nonlinearity. Based on this generalized result, we propose mean and covariance functions for building GP emulators that capture the approximate conditional linear effect of the coefficients. Numerical simulations demonstrate the substantial improvements in prediction performance achieved with the proposed emulator. Matlab codes for reproducing the results in this article are available in the online supplement.     

测量高斯光分布半宽度的光电共轭方法

测量光电信号与参考光电信号来自同一光电器件,形成一对共轭函数。调整参考光电信号 放大器的正电源电平,使之等于测量信号的峰值,此时两函数共轭交点之间的距离即对应于光束的半宽。测量过程中,被测光束能量的缓慢变化并不对结果造成影响,因此稳定性较好,实验重复精度至±2mm。