SU1303817A1 - Device for measuring displacement vector of diffusely reflecting film - Google Patents

Abstract

This invention relates to a measurement technique. The purpose of the invention is to improve the measurement accuracy by eliminating the error associated with the presence of additional interference patterns formed in the focal plane of the lens. When the raster 6 is moved, the interference fringes are modulated, and the photodetector 8 of the measuring channel detects a periodically varying light signal. The phase of the reference channel signal remains constant. The signals of both channels are fed to the inputs of the meter 10 phase difference. 1 il. eight . with about oo 00

Description

The invention relates to a measurement and control technique and can be used to measure a displacement vector of diffusely reflecting objects,

The aim of the invention is to improve the accuracy of measurements by eliminating the basic measurement error associated with the presence of additional interference patterns that are arranged in the focal plane of the lens.

The drawing shows the scheme of the proposed device

The device contains a source of coherent radiation I, an interferometer 3 of a shear interferometer 3j installed along the radiation of a speckle photograph 2j, installed along the beam of the measuring channel, a deflecting element 4 installed along the beam of the reference channel, a lens 5 mounted along the beam

rays of both channels, a regular slit raster 6 installed in the rear focal plane of the lens, photo detectors 7 and 8 installed along the beams of the reference and measuring channels, a resonant filter 9 whose input is electrically connected to the output of the photodetector 8, meter 10 phase difference, two inputs of which are connected to the photoacceptor 7 and the output of the resonant filter.

The device works as follows

The non-broadening beam of the coherent radiation source 1 illuminates the speckle photograph 2, on which the investigated object is registered in a disturbed and unperturbed state. The spreading speckle photograph propagates light through the measuring channel, directly passing through the reference channel, In the measuring channel, the speckle - the photograph shows the interferometer 3 shift, which serves to adjust the period of interference fringes. The interference pattern is formed in the rear focal plane of the lens 5 on the surface of the raster 6. A slit cylindrical raster can be used in the device. When moving (rotating the raster 6, the interference fringes are modulated, and the photodetector 6 of the measuring channel records the time-varying light signal , The time dependence of the first harmonic signal at the output of the photodetector 8 is

  Aco5 (s7-l-4 l,

c6

where A is the amplitude of the first harmonic f

57 - first harmonic frequency;

fu

CP - dsino6- first harmonic phase

ki;

cf is the displacement vector; / is the wavelength of the light of the coherent radiation source; , the angle of diffraction of light in speckle photography (the angle between the reference and measuring channels).

In the signal phase, as can be seen from () (contains information about the blending vector.

The deflecting element 4, the lens 5 and the raster 6 form the signal of the reference channel from the light that directly passed the speckle photograph. When moving the speckle photograph relative to the illuminating beam, the phase of the signal of the measuring channel changes in accordance with the change of the displacement vector. The phase of the reference channel signal remains constant. The signals of both channels are fed to the inputs of the meter 10 phase separation. The change in the displacement vector ud is determined from the expression

40

 elnci j

five

0

five

where Ds) is the difference between the readings of the phase difference meter, corresponding to the two positions of the speckle photograph; Cid is the change in displacement vector. The resonant filter 9 serves to suppress the higher harmonics contained in the signals (e of the measuring channel at the output of the photodetector 8). The filter is tuned to the frequency of the first harmonic S7.

The device is tuned using the shift interferometer 3 so that the period of the interference fringes becomes equal to the raster period. In this case, the amplitude of the first harmonic of the signal of the measuring channel will be maximum.

313038

Thus, the proposed implementation of the device while suppressing higher harmonics by 20 dB allows one to measure the displacement vector with an accuracy not worse than the A / 1000 band.

Claims (1)

Invention Formula An apparatus for measuring the displacement vector of a diffusely reflecting object, comprising a coherent radiation source, intended to form a reference and measuring optical channels from the object, a shear interferometer and a photodetector arranged in series along the beam of the measuring optical channel, the second photodetector being installed along the beam optical reference channel, lens placed imbalance with a shear interferometer and photodetectors, and common to both channels, and a phase difference meter, two inputs of which are connected to the corresponding photodetectors, which are different, with the aim of turning the accuracy one because of measurements, it is equipped with a deflecting element installed along the beam of the reference channel in front of the lens, a regular slit raster installed behind the lens in the rear focal plane with the possibility of moving perpendicular to the optical axis of the lens, and a resonant filter installed between the first photodetector and the meter phase differences, and the large side of the raster slit is perpendicular to the plane of intersection of the channel rays.