图6-4 机械法移相原理图
6.1.2 激光干涉测长系统的组成

除了迈克尔孙干涉仪以外，激光干涉测长系统还包括激光光源、可移 动平台、光电显微镜、光电计数器、显示记录装置
7.干涉条纹计数时，通过移相获得两路相差π/2的干涉条纹的光强信号， 该信号经放大，整形，倒向及微分等处理,可以获得四个相位依次相差 π/2的脉冲信号（图6-5）。
图6-5 判向计数原理框图
激光干涉测长仪chelson interferometer( the core part) Laser source( Single-mode helium neon gas laser;Output for 632.8 nm red wavelengths) Mobile platform( Along the direction of incident light translation) Photoelectric microscope Photoelectric counter Display record device( Output measurement results, can be replaced by special computer or PC)
基本原理
The Michelson interferometer is shown in Figure 1. The basic optical path of laser interferometer length measurement is a Michelson interferometer, and this makes use of interference fringes ,which are the traces of points owing the same path difference, to reflect the information of measured object. It uses the partially reflecting element P to divide the light from laser source into two mutually coherent beams which are reflected by M1 and M2 .The output intensity of an interferometer is a periodic function of the length difference between the measuring path and the reference path of the interferometer. Typical length measurements with a laser interferometer are performed by moving one reflector of the interferometer along a guideway and counting the periodic interferometer signal, e.g. the interference fringes. These results are unambiguous as long as the length difference between two consecutive measurements is within λ/2. Interpolation of the fringes can lead to a resolution of the length measurement below 1nm. The bright fringes occur when the path difference is kλ and the dark fringes when it is (k+1/2)λ,where k is any integer.
6.1 激光干涉测长
激光干涉测长

干涉测量技术是以光的干涉现象为基础进行测量的一门技术 6.1.1 干涉测长的基本原理
1. 激光干涉测长的基本光路是一个迈克尔逊干 涉仪,如图6-1示,用干涉条纹来反映被测量的信息。 两束光的光程差可以表示为
ni li n j l j
i 1 J 1
He-Ne Laser
computer
Detector module
A brief introduction about Michelson
Albert Abraham Michelson(1852~1931) was born in what was then Germany (now Poland) and emigrated with his family to the United States in 1855.He became a professor of physics at the Case School of Applied Science (Cleveland, Ohio), then at Clark University( Worcester, Massachusetts), and then at the University of Chicago. In 1907 he became the first American to receive a Nober prize; the prize citation reads: “For his optical precision instruments and the spectroscopic and meteorological investigations carried out with their aid.”
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2.被测长度与干涉条纹变化的次数 和干涉仪所用光源波长之间的关系是 3.从测量方程出发可以对激光干涉 测长系统进行基本误差分析
L N L N
即L N
图6-1 激光干涉测长仪的原理 图
6.1.2 激光干涉测长系统的组成
1. 除了迈克尔逊干涉仪以外，激光干涉测长系统还包括激光光源，可移动平台，光电显微 镜，光电计数器和显示记录装置。 2.迈克尔逊干涉仪是激光干涉测长系统的核心部分，其分光器件、反射器件和总体布局 有若干可能的选择 3.干涉仪的分光器件原理可以分为分波阵面法、分振幅法和分偏振法 分振幅平行平板分光器和立方棱镜分光器 偏振分光器(参见图6-6中的B2)以及由晶轴正交的偏光棱镜组成如沃拉斯顿棱镜
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4.干涉仪中常用的反射器件:平面反射器、角锥棱镜反射器（图6-2a）、直角棱镜反射器 （图6-2b）、猫眼反射器（图6-2c）
图6-2 反射器
6.1.2 激光干涉测长系统的组成

5.激光干涉仪的典型光路布局有使用角锥棱镜反射器的光路布局，如图6-3示。
图6-3 典型光路布局
6. 移相器也是干涉仪测量系统的重要组成部分。常用的移相方法有机械移相（图64），翼形板移相，金属膜移相和偏振法移相。