Diffraction Efficiency of Attenuated Sinusoidally Modulated Gratings in Volume Holograms

Based on the theory of coupled waves the amplitude of the first-order diffracted wave and the diffraction efficiency respectively is calculated for an attenuated sinusoidally modulated grating using suitable approximations. Solutions for absorption, lossless dielectric, and mixed holograms in transmission and reflection are given. It is shown that the attenuation acts as a decreasing factor of the effective thickness of the storage medium. A deviation of Bragg-angle incidence shows an increasing and shifting of the secondary minimum and maximum values related to the normalized maximum value caused by attenuation.     

Contour Mapping of the First and the Second Derivatives of Plate Deflection by Using Modulated Diffraction Gratings Made by Double-exposure Holography

A method is presented to determine contour maps of the first and the second derivatives of the deflection of an elastic bending plate. The deflection of a rough surface object is recorded once as a modulated diffraction grating. One of the diffracted waves is spatially filtered and brought into a shearing interferometer. The resultant shearing interferogram depicts contours of the first derivative of the deflection. The second derivative is obtained from the second modulated diffraction grating which is made with the interferogram of the first derivative. By recording the grating non-linearly, it is possible to obtain a substantial increase in the sensitivity of the interference fringes.     

Effect of Vibration on the Visual Telescopic Imaging of Sinusoidal Gratings

Abstract

On many occasions observers using telescope and sighting instruments see an image subject to an oscillatory displacement. It is of interest to the designers and users of these optical instruments to know in a quantitative way how such image oscillation will affect overall performance. This paper describes a set of laboratory experiments undertaken in carefully controlled conditions to study this problem in terms of its effect on the contrast sensitivity function of observers as they looked through a 10 × telescope at sinusoidal grating targets. The experiments show that observers perform this task surprisingly well, obtaining results that are hard to explain in terms of simple modelling.     

Vibration Analysis by Speckle Counting

A method for the simultaneous determination of the amplitude and frequency of in-plane vibrations is described, based on a velocity measurement within small time intervals made by analysing the moving speckle pattern. This is done by counting the intersections between the actual speckle intensity and a threshold given by the mean intensity, which is evaluated by spatial integration of the speckle intensity with the aid of an aperture of appropriate diameter, thus avoiding the use of any time constant. A special control measurement enables the inversion point of the vibration to be detected precisely, which enables the frequency to be determined, even if shot noise is not negligible.     

齿轮振动中调频信号的解调方法及仿真计算

齿轮发生裂纹故障时其振动信号会产生调制现象，包括幅值调制和频率（相位）调制两部分。目前调幅信号的解调分析已经比较成熟，但对于调频信号的解调方法研究还不够完善。全面系统介绍了近年来处理调频信号中最常用的希尔伯特相位解调和循环平稳解调两种方法，并通过仿真指出了这两种方法各自的优缺点和局限性。     

Grazing Diffraction by Volume Phase Gratings

Light diffraction by a volume phase grating with slanted fringes is considered. An analytical solution of the system of second-order coupled wave equations is obtained and applied to the problems of grazing diffraction by a transmission grating. It is shown that a strong backward diffracted wave arises, demonstrating that the grating can behave simultaneously as a transmission and a reflection grating. The diffraction efficiency balance and angular selectivity are analysed.     

重叠体光栅相干组束的耦合波分析

目前基于重叠体光栅的相干组束系统还没有完整的理论模型和参数分析,针对这个问题,本文采用耦合波理论,建立了比较完整的基于重叠体光栅的双光束组束模型,给出了各光束在重叠体光栅内传播的解析解.模型表明,基于重叠体光栅的双光束组束系统其输出光强受两入射光的振幅和位相、体光栅间的相移和折射率调制振幅、光栅厚度,失谐量等多个光学参数的影响.通过数值计算,详细分析了各光学参数对组束结果的影响.最后总结了设计高效重叠体光栅相干组束系统时必须遵循的条件,如必须对光栅厚度进行优化、各光栅的折射率调制振幅必须相同,保证失谐量足够小等.     

斜拉索受轴向激励引起的面内参数振动分析

考虑拉索垂直及几何非线性的影响，导出了拉索在轴向激励作用下的非线性振动方程，用谐波平衡法得出了产生参数共振的最小激励幅值，共振时瞬态和稳态的振幅值及拉索内力的变化特性，论述了结构阻尼对参数振动的影响，并对典型斜拉索进行了数值求解，研究结果表明，参数振动的响应特性与Irvine参数，频率匹配，激励幅值，倾斜角度等有关，索内力在瞬态现稳态有较大的变化，索的瞬态内力不容忽视。     

线性调频信号在低频振动校准系统中的应用

针对某低频(0.01～20Hz)电动振动台校准系统存在的校准时间长、精度低、费用高等不足,利用虚拟仪器技术对其进行扩展和完善;针对原系统由于采用单频正弦信号进行人工扫频的校准方法,而导致的校准时间长,且对于被校传感器的某些谐振点无法精确测得等缺点,介绍了采用低频段内的线性调频信号作为激励信号的校准方法,有效地实现了一定频率段内快速、高精度的校准.提出了在校准过程中将调频信号校准方法和正弦信号校准方法有机结合的新方案.通过理论分析和试验结果表明,此校准方法具有较好的实用价值.     

锻锤基础振动分析及非连续屏障隔振探讨

通过重型锻造车间的环境振动测试，对重型锻锤激励可引起的地基振动信号进行分析，并讨论了已有锻锤隔振基础的改造和非连续屏障的隔振效果的计算及其可行性。     

基于光折变光栅的可调谐滤波方案及特性分析

在LiNbO3单模波导上利用双光束干涉可形成光折变波导光栅,针对粗波分复用系统提出了通过实时改变双光束之间的夹角进而改变光栅间距,实现可调谐滤波的方案.利用光折变动力学理论,得到光栅调谐时间在毫秒数量级.研究发现,适当提高光强和增加杂质掺杂浓度可提高衍射效率、减少光栅初次建立时间.基于耦合波理论的数值模拟结果表明,增大光栅长度能使衍射效率提高且带宽变小,而增加折射率调制度使衍射效率提高但同时带宽变宽.在折射率调制度为8×10-5,光栅长度大于12mm时,可获得91％以上的衍射效率和小于0.08 nm的带宽.     

Analysis of Far-field Diffraction Characteristics of Wavelength-sized Surface Relief Gratings

The rigorous boundary matching technique was used to analyse the far-field diffraction from wavelength-sized surface relief gratings for TE polarization. Diffraction characteristics of such surface relief gratings were studied as functions of complex refractive index, groove depth and the angle of incidence. The surface field at the bottom of the grooves is more severely influenced by the edges and walls for metallic material than dielectric ones. The reflectivities of gold gratings show significant fluctuation for different incident wavelengths. This can be clearly seen from the fact that the zeroth-order diffraction efficiency DE ₀ of gold is lower than that of aluminium at u = 0·4 wm but higher at u = 1·0 wm. It is also shown that the depth of the grooves has significant influences on the diffraction efficiencies, an optimum depth can be chosen to minimize the specular component. However, this optimum depth value is found to be different for the gratings of different materials, e.g. aluminium and gold, although the gratings have exactly the same size and shape. The effect of the incident angle, particularly at critical angles when certain diffracted waves are just about to be cut off was discussed. The zeroth-order diffraction efficiencies are found to change noticeably at the critical angles.     

旋转摩擦诱发粘滑振动特性分析

把旋转体和与弹性梁固结的质量块作为一对摩擦副,研究了旋转摩擦诱发质量块的粘滑运动规律.理论分析和仿真结果表明,旋转摩擦诱发质量块的运动是周期性的非常规振动,其运动过程为质量块先随旋转体一起粘滞运动,然后沿粘滞运动方向滑动,再沿相反方向滑动,无论在粘滞期还是在滑动期,质量块都在运动.这一运动重复进行,直到质量块脱离旋转体或旋转体停止转动为止.     

复杂振动引起的图像退化分析与仿真

平台振动导致光学系统在曝光时间内与景物产生相对运动,严重影响了成像质量,而图像的退化模式可能并不单一,针对目前难于仿真高阶多模的复杂振动引起的图像退化问题,提出了基于像移矩阵的微分动态像移路径图像退化法,全面考虑了振动的空域和频域特性对图像退化的综合作用.从而在实际应用中只要已知振动函数,便可以通过一幅清晰的图像仿真得...     

地铁引起的建筑结构振动及噪声分析

针对上海地铁附近某拟建建筑的振动与噪声问题,建立结构的有限元模型,输入场地实测地面振动加速度激励,计算结构振动的加速度响应.结合噪声预测模型,给出建筑结构内声场分布规律,并结合工程实例,对浮筑楼板隔振降噪措施效果进行分析,结果表明浮筑楼板隔振降噪效果一般.     

地铁引起建筑物振动舒适度分析

针对上海地铁附近某拟建建筑的振动舒适度问题,建立结构的有限元模型,输入场地实测地面振动加速度激励,计算结构振动在时域内的响应.结合烦恼率模型,给出了基于烦恼率模型的建筑物振动舒适度分析方法,同时将分析结果与使用振动舒适度标准获得的结果进行比较,结合算例分析表明,这两种分析方法给出的分析结论基本一致,而烦恼率方法则具有更为定量化的特点.     

推进轴系纵向振动引起的艇体声振特性分析

螺旋桨在艇体艉部不均匀伴流场中旋转产生的脉动推力激励起推进轴系纵向振动,振动经推力轴承基座传递至艇体,引起艇体水下低频辐射噪声。通过建立推进轴系、推力轴承基座和艇体耦合结构模型,分析推进轴系─艇体的耦合振动模态,结果显示,艇体弹性支撑边界条件对推进轴系的纵向振动特性有一定影响。采用基于模态叠加法的有限元结合边界元方法分析推进轴系纵向振动激励下的艇体水下辐射声场,分析表明,艇体第1阶纵向振动模态是参与艇体水下声辐射的主模态。进一步在推力轴承及其基座间安装动力吸振器以减小推进轴系纵向振动向艇体的传递,使艇体水下辐射噪声得到一定程度上的控制。