SU1231400A1 - Interferometer for inspecting quality of plane surfaces - Google Patents

Abstract

The invention relates to measurement instrumentation and is used to control the quality of the flat surfaces of objects. The purpose of the invention — to improve the accuracy of control — is achieved by eliminating the distortion of the interference pattern. The reference beam, formed by reflection from the beam splitter, passes through the mirror element and the light coupling to the observing system. The working beam passes through the beam splitter, the object located in the holder and the light connector, where it is combined with the reference beam and interferes with it. The light coupler and the beam splitter are located in the radiation flux in such a way that the same radiation path length is provided in the working and reference beams to eliminate the aberrations of the lighting system. When combining the image of the pupils of the working and exemplary beams with the introduction of the lens by rotating the holder after removing the lens with the help of a mechanism, an interference pattern is observed, the curvature of the body of which characterizes the deviation from the plane. 2 Il. with S (L

Description

f

The invention relates to measuring technique. It can be used to control the quality of flat surfaces of objects, in particular, to control deviations from the flatness of the rough surfaces of objects of complex configuration,

The purpose of the invention is to increase the control accuracy by eliminating the distortion of the interference pattern.

FIG. I presents a schematic diagram of the interferometer; in fig. 2 - calculation of the optical stroke length in the beam splitter and the light coupler.

The interferometer contains successive lighting system, including a laser 1 and a telescopic system 2, a mirror 3 and a beam splitter 4, a mirror element 5 installed in the beam reflected from the beam splitter, an object holder 6 installed in the beam passing through the beam splitter 4, a light connector 7, located in the intersection plane of the interfering beams, a mirror 8 optically coupled to the light coupler 7 and the objective lens 9 of the observing system also including a mechanical assembly 10 for inputting and outputting a lens 11 from the radiation flux, and the interference pattern recorder 12. The beam splitter 4 and light connector 7 are wedge-shaped and oriented in the radiation flux so that the sum of the distance along the radiation between the reflecting surface of the beam splitter 4 and element 5 and the distance along the radiation between element 5 and the light connector 7 is equal to the sum of the optical length of the radiation path in the beam splitter 4 , the distance from the beam splitter 4 to the object holder 6, the distance from the object holder 6 to the light link of the cable 7 and the optical path length of the light connector 7, I

The interferometer works as follows.

in a way.

The radiation from laser 1 passes through a telescopic system 2, which forms a quasi-flat wavefront, and is deflected by mirror 3. to a beam splitter 4, where it is divided into reference and working beams. The reference beam is formed by reflection from the beam splitter

- ten

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4, then it passes to the mirror element 5, is reflected from it, passes to the light linking device 7, is reflected from it by means of a mirror 8

5 enters the observation system. The working beam passes the beam splitter 4, is deflected and obliquely falls on the holder 6 of the object on which the part to be monitored is mounted. After reflection from the controlled surface, the working beam passes the light coupler 7, is combined with the sample beam and interferes with it. Then both beams on 5 are guided by a mirror 8. In the observation system, the lens 9 of which forms the interference pattern in the plane of the recorder 12, the Lens 11 is introduced with the help of the node 10 into the 20 radiated current of the interfering beams so that it observes in the plane 12. with the coincidence of the images of the pupils of the working and reference beams of the interferometer. Combining the images of the pupils is carried out by rotating the holder 6 with respect to. dvzgkh mutually perpendicular axes lying in a plane. Parallel to the mirror element 5,

25

thirty .

The beam splitter 4 and the light beam connector 7 are located in the radiation flux in such a way that the same radiation path length is provided in the working and exemplary beams to eliminate the influence of the aberrations of the lighting system

AB + BC ED-i-EF + n (AD + FC),

(I)

where n is the refractive index of the material of the beam splitter 4 and the light coupler 7. The angle iff of the radiation incident on the monitored surface, which provides a regular wave front for a given roughness, is the initial value for calculating the parameters of the circuit satisfying condition (1), Optical path length splitter and luminer for the axial beam (Fig 2)

nd cos 0

i5in {9 + 8 + ii) r-T, (2)

55 where d is the thickness of the beam splitter and the light connector along the normal to the reflecting surface at point A;

E - wedge angle;

o - beam deflection angle after

passing a wedge; i, is the angle of incidence of the beam on the reflecting surface of the wedge. Since,,,, then from condition (1), taking into account expression (2),

n-d-cos 0

(9111 (e + 1k

Proceeding from i ,,, d, 0, find the constructive parameters of the scheme, if condition (3) is satisfied.

For the convenience of combining the test surface of the part with point E, corresponding to the equality of the length of the radiation path in the working and sample beams, a K-K sighting line can be drawn on the back wall of the interferometer.

Combining the images of the pupils of the working and exemplary beams with the introduction of the lens 11 by rotating the holder 6 makes it possible to observe the interference pattern after removing the lens 11 using the mechanism 10. The frequency and orientation of the bands is adjusted by means of the corresponding inclinations of the holder 6. The curvature of the bands characterizes the deviation from the flatness of the surface, and the price of the band K is defined by the expression:

to

2 cosibj,

where L is the wavelength of the laser radiation 1.

a5

ten

- but

15

20

25

3.0

35

40

Claims (1)

Invention Formula Interferometer for quality control of flat surfaces of objects containing successively located lighting system and a beam splitter, a mirror element mounted in a beam reflected from a beam splitter, an object holder mounted in a beam passing through a beam splitter, a light coupler located in the intersection beams intersecting plane, and observational system containing the object yv and the recorder of the interference pattern, about tl and h and y and 1 with the fact that in order to increase the accuracy of control, he a lens located in front of the recorder at such a distance from it that the back focus of the lens is coupled to the recorder's receiving plane, the mechanical assembly for the input and output of the lens from the radiation flux, and two mirrors, one of which is optically connected to the illuminator and the beam splitter, but. others with a lens and a light-coupler, and a beam splitter and a light coupler are made wedge-shaped and oriented in the radiation flux so that the sum of the distance between the reflector surface of the divider and the mirror element and the distance along the radiation between the mirror element and the light-coupler is equal to the sum of the optical path length of the radiation in the beam splitter, the distance from the beam splitter to the object holder, the distance from the object holder to the body connector and the optical link eskoy stroke length izlucheg in light- connector. at F sriе.2