基于级联光栅的X射线相衬成像实验研究

为避免小周期高宽比吸收光栅的制作,提出了由泰伯-劳干涉仪和逆泰伯-劳干涉仪组成的级联光栅X射线相衬成像装置,该装置利用泰伯-劳干涉仪的自成像作为逆泰伯-劳干涉仪的源.通过实验验证了该方法的有效性,得到了成像系统的莫尔条纹和强度振荡曲线.条纹最高对比度为17.4%,随着吸收光栅偏离零点位置,条纹对比度逐渐降低,但是在其位置跨越从-17mm到12mm的范围内,条纹对比度仍保持在10%以上.实验讨论了样品位置对成像灵敏度的影响,结果表明当样品位置靠近相位光栅两侧时,其成像灵敏度最高.本文的研究可应用于生物医学成像的大视场X射线相衬成像系统的设计.     

基于双光栅的马赫-曾德尔干涉仪的初步研制

设计和初步制备了基于双光栅的等臂和不等臂马赫-曾德尔干涉仪,两个衍射光栅分别用作光束分裂器和光束复合器.来自激光器的平行光束透过第一光栅后产生多柬衍射光,等臂干涉仪使用两个平面反射镜反射两束对称衍射光至第二光栅的同一位置并产生完全重合的衍射条纹,即每束衍射光包含两个成分.利用光探测器监测任一束重合的衍射光束,该光束两成分之间的相位差随时间的变化就能够被准确测定.而不等臂干涉仪仅使用一个反射镜反射某一束衍射光并使之与零级光束透过第二光栅后产生完全重合的衍射条纹.通过使用一个厚度为50μm的玻璃片来改变相位差,对不等臂干涉仪的干涉效果进行了测试,得到了与理论值相符的实验结果.     

双棱镜改变写入Bragg波长的相位掩模技术

将一种可旋转的双棱镜引入到相位掩模技术中以改变光栅的写入Bragg波长.在该系统中,光纤光栅是由来自可旋转双棱镜所形成的波长为248 nm的紫外干涉条纹写入的,其中,相位掩模被用作 1级衍射光的分束器,通过双棱镜的旋转可改变两写入光束的交叉角.为了初始化Bragg波长的参考值,双光栅的顶角由相位掩模的 1级衍射角和双棱镜的折射率确定.因为在～100 nm范围内两光束的非对称旋转对光栅周期的改变是5×10~(-4) nm,双棱镜引入的光栅的闪耀可忽略.当Bragg波长的移位为1 nm时,棱镜最大的旋转角为～1 degree,最小的旋转角是～2.4 min.与Talbot干涉仪中平面镜的旋转角～23 s/nm相比,该相位干涉仪中棱镜的旋转精度降低了2～3个数量级.     

利用迈克尔逊干涉仪制备全息光栅

利用迈克尔逊干涉仪上调节出的等厚干涉条纹,将全息干版放置在观察屏处曝光,经过处理后得到全息光栅,利用分光计测出光栅常数.     

浅议莫尔现象及应用

莫尔(moire)一词来自法文,含义为波动的,或起波纹.在日常生活中,当我们将两块窗纱叠在一起时形成一种不规则明暗相间的花纹,这就是莫尔条纹.现在,莫尔现象已广泛应用于科学研究和工程技术之中,莫尔条纹作为精密计量手段可用于长度,角度、振动等领域的测量.1莫尔条纹的形成将两块参数相近的透射光栅以小角度叠合,将产生放大的光栅.如图1和图2为两块光栅常数相同的光栅A和B,叠合后得到如图3所示的放大光栅即莫尔条纹.     

部分相干光栅衍射效应和干涉术

本文提出一种新的部分相干照明的光栅衍射干涉仪.先分析了光栅的介于Talbot和Lan效应之间的部分相干衍射效应.部分相干干涉图的特点是条纹由频率成倍的两种光栅状载波所表征.调整光源狭缝,系统在两相干性极端分别转成Talbot和Lau干涉仪.理论分析采用了模糊函数方法.最后给出了实验.     

叠栅条纹和CCD用于位移和角度的测量

将叠栅条纹测量技术和CCD器件结合应用于角度和位移的智能测量系统,该系统利用光栅的衍射自成像现象产生虚拟光栅,与另一光栅形成叠栅条纹,并用CCD光电转换系统,测量叠栅条纹的距离,可得到两光栅间的夹角.当任意一片光栅沿垂直于栅线方向移动时,通过数出移过叠栅条纹数目,即可得到相应光栅移动的位移.本文还分析和讨论了误差来源及给实验带来的影响.     

光载波条纹图的计算机辅助分析——阶梯形虚拟光栅解调法

本文提出一种两维光测条纹图的相位测量技术--阶梯形虚光栅解调算法。此法只需要获取一幅光载波条纹图,由计算机产生两个由N(整数)个象素构成、透射函数呈阶梯形分布、彼此间有一定相位差的两个虚光栅(参考信号),通过在整数域的运算实现对条纹图和虚光栅的相乘型叠加,低通滤波后得到两个相位差已知的叠栅函数,然后从两个相差为已知值的正弦信号中提取相位信息。理论分析和计算机模拟表明,具有相当高的测量精度,计算简便快捷。文中还给出了阶梯虚光栅解调法在投影光栅法三维形貌测量中的应用实例。     

光栅成像与Lau效应

本文推导了两个光栅干涉仪的光强分布。分析了光栅周期与狭缝宽度比值对Lau条纹的影响。指出有β>p/(2a)的清晰的Lau条纹存在,并在数值计算与实验上加以证实。 关键词：     

用空间滤波方法制作θ调制全息物片

给出了一种制作θ调制全息物片的新方法.在空间滤波光学系统的频谱面上放置只允许±1级频谱通过的滤波器,当单色平行光垂直照射物平面上的一维光栅时,将在像平面上得到两个重叠的一维光栅像,同时在成像区域形成光强按余弦规律变化的干涉条纹.用装有镂空模板和全息干版的可旋转组合干版夹对干涉条纹进行3次等时曝光,记录下3种不同干涉条纹方向的图案,即可制作出θ调制全息物片.     

Multiplexed fiber Fabry-Perot temperature sensor system using white-light interferometry

A novel monitoring system for a fiber Fabry-Perot interferometer (FFPI) temperature sensor has yielded a resolution of 0.013 degrees C (0.0025 fringe). Light from a broadband source passes through a scanned Michelson interferometer and is reflected from a FFPI to produce a fringe pattern, the temporal position of which is proportional to a change in the optical length of the fiber interferometer. A second Michelson interferometer with a distributed-feedback laser source is used to correct for variations in the translation rate of the motor-driven scanning mirror. Coherence multiplexing of three such sensors has also been demonstrated.     

Optical transfer function analysis of Lau-Type grating atom interferometer

A grating interferometer composed of two transmission gratings in tandem irradiated incoherently was studied for an atom interferometer. Determination of its interference effect was made with consideration of the optical transfer function. An atom beam had a velocity distribution, which made the influence on the interference phenomenon. The calculated results show that the fringe (grating image) with relatively high contrast is obtained under a certain grating arrangement even if the interferometer is irradiated by a spatially incoherent polychromatic atom beam.     

Waveform Measurement of Ultra-Short Optical Pulses Based on Two-Photon Absorption in Si-Image Sensor

We demonstrate a novel waveform mesurement system of ultra-short optical pulses based on the two-photon absorption process in a Si-image sensor. Using an interferometer with a tilt mirror in the reference path, the relative time difference between the signal and reference pulses is spatially distributed on the Si-image sensor, so the intensity auto-correlation is monitored as an image at a time without using moving parts. This system can create or remove an interference fringe pattern overlapped on the auto-correlation image by controlling the polarization states of the laser pulse, which is useful for measuring the crossing angle between the signal and reference beams as well as avoiding contamination of the interference fringe into the auto-correlation image. We successfully measured optical pulses less than 100 fs from a fiber ring laser with a temporal resolution of 0.4 fs. The obtained waveform agreed well with that observed with a conventional second harmonic generation (SHG) based auto-correlator.     

An in-plane insensitive multiaperture speckle shear interferometer for slope measurement

A modified two-aperture speckle shear interferometer that eliminates the contribution of the in-plane component and its derivative to the phase change, and yields a fringe pattern corresponding to the first-order partial derivatives of the out-of-plane displacement component, is reported in this note. In this method, two laterally sheared object points are viewed axially. The wave fields from these points are independently combined at the image plane of the imaging system.     

基于CCD采集的Mach-Zehnder干涉条纹图的处理算法

Mach-Zehnder干涉仪适用于研究气体密度迅速变化的状态。由于气体折射率的变化与其密度的变化成正比,而折射率的变化将使通过气体的光线有不同的光程,因此可通过干涉臂变化对干涉条纹图像效果的影响得到气体密度。实测中,采用图像采集卡和CCD来接收Mach-Zehnder干涉仪产生的条纹图像,再通过计算机对条纹图像的条纹间距进行处理,从而得到气体密度的变化状态。从光干涉理论出发,对Mach-Zehnder干涉条纹图像特征进行了分析,建立了Mach-Zehnder干涉条纹的数学模型,并根据此模型设计了处理Mach-Zehnder干涉条纹图像的算法。算法包括图像的预处理(即图像的噪声提取)、图像的二值化及图像的细化。     

一种新型莫尔条纹的生成方法及应用

通过对Mach-Zehnder干涉仪光路的改装,得到了一种新型的莫尔条纹生成方法.利用CCD接收并将图像采集到计算机上进行了观测,对莫尔条纹参数和性质作了分析,最后对其应用进行了研究.     

采用整体最小二乘法的条纹图配准方法

针对共光路菲索型动态干涉仪采集到的4幅条纹图的空间一致性问题,本文提出一种新的条纹图配准思路,将条纹图与图像配准在关联度上人为分开,搭建了专用的图像配准装置,避免将条纹与十字丝标志点混在一幅图像内而影响干涉仪的测量精度。首先通过本文搭建的条纹图配准装置对4台CMOS相机进行物理配准,然后利用整体最小二乘法对采集到的同一十字丝刻划板图像进行十字丝提取、交点计算以及旋转量计算,实现共光路菲索型动态干涉仪条纹图像的点点对应。最后通过试验对比验证,证明了本文算法的配准精度优于模板重心法的配准结果,互相关度达到96%以上。     

Determination of interferometer phase distributions by use of wavelets

A new technique for directly extracting phase gradients from two-dimensional (2-D) interferometer fringe data is presented. One finds the gradients by tracking the maximum modulus of the continuous wavelet transform of the fringe data and the phase distribution that is obtained, with a small error, by integration. Problems associated with phase unwrapping are thereby avoided. The technique is compared with standard methods, and excellent agreement is found. In common with Fourier-transform methods, the technique is capable of extracting the full 2-D phase distribution from a single image.     

Modeling of the fringe shift in multiple beam interference for glass fibers

A quadratic model is suggested to describe the fringe shift occurred due to the phase variations of uncladded glass fiber introduced between the two plates of the liquid wedge interferometer. The fringe shift of the phase object is represented in the harmonic term which appears in the denominator of the Airy distribution formula of Fabry-Perot’s interferometer. A computer program is written to plot the computed fringe shifts of the described model. An experiment is conducted using liquid wedge interferometer where the fiber of a nearly quadratic thickness variation is introduced between the two plates of the interferometer. The obtained fringe shift shows a good agreement with the proposed quadratic model. Also, it is compared with the previous theoretical shift based on ray optics of semi-circular shape.