RU1793204C - Laser interferometer for measuring object linear displacements - Google Patents

Abstract

The invention relates to measuring technique and can be used to measure linear displacements with high accuracy. The purpose of the invention is to improve the accuracy and speed of measurement. The interferometer contains a source of two-frequency radiation, optically coupled to polarization and non-polarization beam-splitting cubes, two reflectors and two photodetectors connected to an electronic computing unit. A two-mode laser is used as a radiation source, and each photodetector consists of an A / 4 phase plate, a polarizer and a photodiode operating at the intermode beat frequency. 1 ill.

Description

The invention relates to measuring technique, namely to laser interferometry, and can be used for measurements with high accuracy of linear movements of objects.

Closest to the proposed device is a laser interferometer containing a two-frequency radiation source, optically coupled non-polarization and polarization beam-splitting cubes, two reflectors of the reference and measuring arms of the interferometer, and two photodetectors, which are connected electrically to an electronic computer unit .

The aim of the invention is to increase the accuracy and speed of a laser interferometer.

This goal is achieved in that the two-frequency radiation source is made in the form of a two-mode frequency-stabilized laser, and each photodetector consists of an A / 4 phase plate, a polarizer and a photodiode.

The drawing shows the proposed interferometer.

The device contains a monochromatic radiation source 1 operating in the mode of generation of two longitudinal modes, polarizing 2 and polarizing 3 beam-splitting cubes optically associated with it, reflectors 4 and 5 of the reference and measuring arms of the interferometer, and two photodetectors 6 and 7. Each The photodetector consists of a quarter wave phase shifting plate 10, a polarizer 11, and photodiodes 12 operating at an intermode beat frequency. The outputs of the photodetectors are connected to the electronic unit R and the digital indication unit 9.

The radiation of a monochromatic radiation source is two radiation modes with orthogonal linear polarizations and differing in frequency at 640 MHz. After reflection from the beam splitting face of the cube 2, both polarizations arrive at the photodetector 6.

with C

4 Yu GJ

Yu

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The phase A / 4 plate 10 is oriented so that its main axis is at angles of 45 ° to the polarized components of the laser radiation. Two orthogonal circular polarizations with the same frequency difference are formed at the output of the phase plate. Polarizer 11 passes linearly polarized different-frequency radiation to the photodetector 12. As a result of optical heterodyning, an electrical signal appears at the output of the photodetector at an intermode beat frequency of f0 640 MHz

Uo Uosln2 fot, (1) where U0 is the signal amplitude,

The laser radiation transmitted through cube 2 is incident on the polarization cube 3 of the Michelson interferometer, in which it is divided by polarization. When reflected from the measuring and reference reflectors of the interferometer, the rays with different polarizations are combined on the same cube and the device 7 is transmitted to the photodetector, whose output there is an electric signal at a frequency to, similar to (1).

The device operates as follows. . ,. :;. :; . ..;

When moving the measuring reflector 5, mounted on the moving part of the machine, relative to the reference reflector 4 with a cube 3, the frequency of the electric signal at the photodetector 7 changes by the value of the Doppler shift

XMt)

where v (t) is the speed of the object; A is the wavelength of light; t time

When the reflector 5 moves towards the cube 3, the signal frequency at the photodetector 7 increases, and when moving in the opposite direction it decreases by the amount (2). The signals from the photodetectors 6 and 7 are fed to the electronic unit 8, where they are amplified, converted in frequency and fed to the digital display unit 9. In the latter there is a measurement of the phase shift of the signals of the photodetectors 6 and 7, equal to -

Dr. Г0 (t) dt V (t),

-TgLV (t), (3)

Where X is the movement of the reflector 5; . k is the optical wave number, k 2 l / A. The digital display unit 9 represents the displacement value X in digital form with a resolution of A / 8 or A / 64.

Formulas of the invention

A laser interferometer for measuring linear displacements of an object, containing a source of two-frequency radiation, optically coupled non-polarization and polarization beam-splitting cubes, two reflectors of the reference and measuring arms of the interferometer, and two photodetectors, which are connected electrically to an electronic computer unit, characterized the fact that, in order to improve the accuracy and speed of measurement, the source of two-frequency radiation is made in the form of a two-mode frequency-stabilized laser, and Each photodetector consists of an A / 4 phase plate, a polarizer, and a photodiode.

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