SU1525446A1 - Interferometer for measuring linear displacements of object - Google Patents

Abstract

The invention relates to a measurement technique and can be used to measure displacements and lengths of objects, in particular in the manufacture of integrated circuits. The purpose of the invention is to improve the accuracy of measuring the linear movements of an object, which is achieved by increasing the number of reflection cycles by introducing additional retroreflective systems. The light beam from the coherent source 1 passes through the 2 λ / 8 plate and is divided by the beam splitter 3 into two beams. Each of these rays is directed to one of the branches of the interferometer consisting of successively located first retroreflective system, for example, 14, corner reflector 18 and second retroreflective system 16. The number of cycles of reflection of the beam by systems 14 and 16 is determined by the geometric parameters of reflectors in retroreflective systems and the coherent radiation source 1 parameter — the beam diameter. The other branch of the interferometer is made similarly. After reflection in both branches of the interferometer, the rays interfere with the divider 3 of the beam. The photoelectric unit 12 registers the number of interference fringes and the direction of their displacement as a result of the movement of the carriage 13. 1 Cp f-ly, 6 ill.

Description

The invention relates to a measurement technique and can be used to measure displacements and lengths of objects, in particular in the manufacture of integrated circuits.

The aim of the invention is to increase the accuracy of measuring linear movements of an object by increasing the number of cycles of reflection of the beam by introducing additional retroreflective systems.

Figure 1 is a schematic diagram of the interferometer; figure 2 - diagram of the retroreflective system; on

fig.Z - schematic retroreflective system, left view; figure 4 - the relative position of the angles of the reflectors in the retroreflective system; on Lig.5 - the course of the beam in light-return systems of one branch of the interferometer; figure 6 is a functional diagram of the photoelectric unit.

An interferometer for measuring the linear displacements of the object (Fig. 1) contains a source of coherent radiation 1, installed along the course of radiation of the first plate 2 and a divider 3 of the radiation beam, which

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optically coupled to mirrors 4 and 5, a second plate 6 L / 8, which is optically connected to mirror 7, and a second beam divider 8, to which the mirror 9 is optically connected, two polroids 10 and 11, optically connected to the divider 8 a beam and a mirror 9, a photoelectronic unit 12, whose inputs are optically coupled by t-polaroids 10 and 11, a carriage 13, two retroreflective systems 14 and 15, installed in each branch of the interferometer, one of which is optically connected to the mirror 5, and the second - with mirror 7, two retroreflective systems

16 and 17, mounted on each branch of the interferometer, two additional corner reflectors 18 and 19, optically coupled retroreflective systems 14, 15 and 16, 17, respectively. Each of the retroreflective systems consists of a corner reflector 2O-23, respectively, mounted on the carriage 13, two corner reflectors, 24, 25, 26, 27 and 28, 29, 30, 31, respectively.

and two mirrors 32 and 33 (FIG. 3), optically coupled to the corner reflector, respectively, 20, 21, 22, 23 and installed in such a way that the corner reflectors are respectively 24 and 28 (FIG. 1), 25 and 29, 26 and 30, 27 and 31 Perpendicular to the edge of the corner reflector, respectively 20, 21V 22, 23, the bisectors of the right angles of displacement: parallel to each other by the distance determined for the corner reflectors 24, 25 28, 29 of the light reflecting systems 14 and 15 by the formula

8i "0.5 d (jh - 1),

and for corner reflectors 26, 27, 30, 31 retroreflective systems 16,

17 according to the formula

5, 0.5-d -j, where d is the coherent beam width

Sveta;

j is a more natural number, determined from the expression I6j + 48J + 16 n,

 n is the multiplication factor of the optical path difference of light rays,

and the midpoints of the mirrors 32 and 33 are located on the bisectrixes of the right angles of the corner reflectors, respectively, 24, 25, 26, 27 and 28, 29, 30, 31. From the edge of the corner reflector, respectively

five

0

five

0

five

0

five

0

five

Actually, 28, 29, 30, 31 parallel to its edge is made for a beam of light a window 34 (figure 4) with a length equal to the length of the edge of this reflector and a width determined by the formula

JO. d (j + 1) 42, with the additional corner reflector, respectively, 18 and 19 being optically coupled through this window 34 to the reflectors, respectively, 20, 21,

22, 23, and the distance between its edge and the edge of the bridge, respectively, 28, 29, 30 and 31 is equal to the width of the light beam, and the distance between the edge and the edge of the reflector, respectively, 28, 29, 30, 31 is selected from the ratio

b dj: n i 16li2 32

The optical axes of the plates 2 and 6 L / 8 are parallel to the plane of polarization of the light beam emanating from source 1. The optical plane of the polaroid 10 is parallel to the plane of the polar 3aiuiH of one of the orthogonal components of the light beam falling on it, and the optical The polaroid 11 plane is perpendicular to the polaroid 10 optical plane. The beam splitters 3 and 8 are designed in such a way that they break the light beam incident on them into two light beams of the same intensity.

The photoelectronic unit 12 (Fig. 6) contains photodetectors 35 and 36, the inputs of which are optically coupled to their polaroids 10, 11 (Fig. 1), and their outputs are electrically connected to the inputs of the movement direction detection unit 37, and the output of the photodetector 35 also connected to one of the inputs of the reversible counter 38, the second input of which is connected to the output of block 37. The output of the reversing counter 38 is the output of the interferometer.

The interferometer works as follows.

The beam from the coherent radiation source 1 passes the 2/8 plate, as a result of which two orthogonally polarized optical signals are formed, broken up by a divider 3 beams into two beams. One of these rays is transmitted by mirrors 4 and 5 to the retroreflective system 14 of the first branch of the interferometer, reflected from which the beam with the help of the reflector 18 is directed to the light locomotive

515

the rotation system 16; - reflected by the retroreflective system 16, the beam with the help of the reflector 18 again hits the retroreflective system 14 and returns with the help of mirrors 5 and 4 to the beam divider 3. The ray path in the second branch is similar. First, the beam passes through the plate 6 and is directed by the mirror 7 to the retroreflective system 15, then through the reflector 19 enters the light-returning system 17, through the reflector 19 is again directed to the retroreflective system 15 and returns to the mirror 7 and 6 A / 8 beam divider 3, where it interferes with the beam from the first branch. The beam path in the retroreflective system is explained in Fig. 5, where M ,, M, ..., Mgg are points of reflection.

nor from reflectors;

M

m:

"one

23

M

la

M

and

M

ta

M

2i

MzzZMS,

- entry points to a window for a ray of light; point of exit from the window for a ray of light.

As the carriage 13 moves, the light beam travels in one branch of the interferometer, and decreases in the other. The difference in the paths of the rays in both branches of the interferometer is determined by the formula

D,

where n is the multiplication factor of the optical path of the beam; Pr - index of refraction

the medium in which the propagation is distributed; X is the movement of the carriage 13. On the other hand, the difference in travel is determined by the expression

Where

P

 X n

(N + LC),

wavelength of radiation;

is an integer number of wavelengths.

25

thirty

counting of light bands, and depending on the direction of movement of the carriage 13 together with the reflectors 20-23, this shift is either negative or positive. The direction of movement of the two signals from the photodetectors 35 and 36 is determined in block 37, which controls the reversing counter 38, which determines the number of pulses occurring during the course of the photodetector 35, representing it in binary code, and also determining the sign displacement, with a logical unit on the sign output of the reversible counter 38 corresponds to a positive displacement, and to a logical zero - negative. The codes for the number of light bars and the mark are the output information of the interferometer.

Claims (2)

1. An interferometer for measuring the linear displacement of an object, containing a carriage designed to communicate with an object, and a sequentially installed source of coherent radiation, an A / 8 plate and divide 45 radiation beams — into two branches, in one of which two mirrors are successively installed and retroreflective system, made in the form of three corner reflectors, located stacked at a distance of - 50 in series so that the second HC n 6 . When the carriage J3 is moved, light strips pass in front of the windows of the photodetectors 35 and 36 (Fig. B), and each light strip corresponds to a change in the optical separation by one light wavelength in a given medium. Photodetectors 35 and 36 convert optical signals at their inputs into sequences of electrical pulses that are shifted relative to each other in phase by 90 what is needed for reversing counting of the light strips, and depending on the direction of movement of the carriage 13 together with the reflectors 20-23, this shift is either negative or positive. The direction of movement of the two signals from the photodetectors 35 and 36 is determined in block 37, which controls the reversible counter 38, which determines the number of pulses appearing at the output of the photodetector 35, representing it in binary code, and determining the sign of the movement, in this case, the logical unit at the sign output of the reversible counter 38 corresponds to a positive displacement, and to a logical zero - negative. The codes for the number of light bars and the mark are the output information of the interferometer. Invention Formula 1. Interferometer for measuring linear displacements of an object, containing a carriage designed to communicate with an object, and sequentially installed coherent radiation source, A / 8 plate and radiation beam divider — on two branches, in one of which two mirrors are installed in series and a retroreflective system made in the form of three corner reflectors located consistently so that the second by U u; UN is a fractional number corresponding to a change in the optical difference within a single radiation wavelength. Thus, the displacement of x caret13 can be represented as During the radiation path, the corner reflector is mounted on a carriage and oriented so that its edge is perpendicular to the edges of two other corner reflectors, and two mirrors, one at a time, on the first and third rays of the corner reflectors, normal bisectors of the corresponding npflhe ix angles of reflectors, on the edge the face of the first along the radiation of the corner reflector is made a transparent window, and in the other branch a second plate, a mirror and a second light returning system are installed in series, made similarly to the first oh and oriented so that the bisectors {: s pr5 {the second radiation angle of the corner reflectors of both European-reversing systems are parallel, the second beam splitter installed at the output of the radiation from both branches, the mirror mounted along the beam reflected by the second beam splitter, two poloid one of which is optically coupled to a mirror, and the other is mounted along a beam divider, a photoelectronic unit optically coupled to polaroids, characterized in that, in order to increase the accuracy of In terms of movement of the object, it is equipped with two corner reflectors, one installed in each branch successively along the beam after the retroreflective systems, and two additional light reflecting systems, made similarly to the first two, installed one after each corner in the branch. reflectors, the second in the course of the radiation corner reflectors in the additional retroreflective systems are located the carriage, the first and third reflectors in the form of two and two additional Yelnia svetovoz, rotational systems are arranged so that the right angles bisectrixes are parallel, and the distance between them is determined by the ratios , 0.5 d j, Si - 0.5 d (j + 1), where d is the width of the radiation beam; j is a natural number determined from the expression n - 16J + 48J + 16, where n is the specified multiplication factor of the optical path difference of the radiation paths; the width of the third edge of the corner reflector in the first two retroreflective systems is determined by the relation: - l jj 20 25 Q 35 40 Bh, i (p- ±., 32 and the distance between the edge of the additional corner reflector in each branch and the edge of the third along the direction of the radiation of the corner reflector, respectively, in each of the first two light reversing systems is equal to the width of the light beam, 2. The interferometer according to claim 1, characterized in that, in order to simplify the construction, the first and third along the beam angular reflectors of each of the first two light-returning systems and the corresponding additional retroreflective system in each of the branches are made in the form of one a corner reflector, on one face of which a reflecting coating is applied so that the reflecting layer is equidistant from the edges of the reflector a quarter of the length of the reflector edge and has a thickness on one half of the 5 s face, and on the other - defined by expressions 42,. If J- 6n- 2 3  12 d (j + 1). and from the edge of the edge along the edge there is a transparent window with a length to the entire reflecting layer and a width determined by the formula (j + 1). Chef Fi9.-5 5