CS204515B1 - Method of making the interference field of the light bundles and laser interferometer for executing the said method - Google Patents

Description

BACKGROUND OF THE INVENTION The present invention relates to a method of generating a light beam interference field for a laser interferometer comprising information about the position and sense of relative motion of the interfering light beams therebetween.

The interference field for technical use, for example for measuring lengths, must always contain information on the direction of movement of the wavefront of one of the interfering beams with respect to the other. This information may be contained either in the Time course of the interference field or in the spatial and phase arrangement of the field.

For use in laser interferometers, an interference field is typically used which results from the interference of two oppositely oriented circular or elliptically polarized beams. In this case, the laser interferometer provides an interference field, from which two signals in the quadrature (phase shifted by 90 °) necessary to detect the direction of movement of the moving part of the interferometer can be obtained.

Such a single interfering laser interferometer, i.e., a single frequency, typically consists of a splitter unit, a slide back reflection system, a detection unit, and a linearly polarized light source, such as a single frequency laser. Typically, a quadrilateral plate is disposed on the axis of the optically magnified beam of a single-frequency laser to convert the linearly polarized laser light into an approximately circularly polarized beam. Behind the quarter wave plate is a separating unit, for example a prism or plate with a separating and partially permeable layer. On this separating layer, the beam is divided into a reference beam and a specific beam. After double reflection on the separating layer, the reference beam exits to the detection unit. The measuring beam first passes through the partially permeable separating layer and proceeds in the original direction to the sliding retroreflection system and, after reflection, returns parallel to the separating layer of the plate, which it partially passes and passes together with the reference beam to the detection unit. At the point where it passes through the plate separation layer, both the reference and measurement beams are united, creating an interference field and advancing to the detection unit along a common axis. The detection unit includes additional splitters (see, for example, U.S. Patent Certificate No. 185014) which further subdivides the beam so that, for example, one portion reflected in one direction passes through the first optical polarization filter and impinges on the first photodetector and the other beam. partially passing through the separating layer of the separating member and passing through the second optical polarizing filter to the second photodetector. By properly rotating the polarizing filters, two signals are shifted by 90 ° (in quadrature), allowing the use of reversing counters for length measurements.

A disadvantage of prior art laser interferometers is that they usually only use circularly polarized light of opposite orientations for both the reference and the specific light beam. Thus, in both of these beams, measures are required to maintain approximately circularly polarized light at the output of the interferometer. In some cases, other optical elements are provided in one branch of the interferometer (reference or measurement), which makes it difficult to maintain approximately circularly polarized light of the beam at the output of the interferometer.

These prior art drawbacks are overcome by a method of creating an interference field of light beams for a laser interferometer comprising information on the position and sense of relative motion of the interfering light beams between them. It is an object of the invention that the interference field is caused by the interference of two beams of light, one of which is linearly polarized and the other circularly or elliptically polarized.

The method allows an interferometer with a detection unit, the principle being that either in the interferometer or in the detection unit in the axis of the specific and reference beam or in the axis of the united beams, second and third polarizing members are provided between the plate and the additional optical members; the linear delay half-wave plate and the third polarizing member is formed by a linear delay quarter-wave plate and a linear half-wave delay plate.

The advantage of said method of creating the interference field of the laser interferometer according to the invention is the possibility of simple arrangement of the laser interferometer and its use in the laser measuring system. The laser interferometer provides a full interference signal and high reliability.

The principle of creating an interference field is as follows: For the input light we assume that for example ° Ί is expressed by Jones vector in the form = 2. Before impinging on the first separating approximately nonpolar ^E ij "" very degrading layer of the light beam passes through the plate with 1/4 azimuth Θ = 45 °, and Jones matrices rotator with rotation angle ξ = 45 °.

For the second reflected beam a2 according to Fig., When we neglect the inflow of the members F, F ^f :

;] n ^eb ° [\ Л _± е ' ^(02/2) 0 ΊΓΟ фк / ¹ ' ² '^ L o V ^ e-MLl oJL 0

For the second released volume b ₂ :

ГД. e ^{ító / 2)} 0 ΊΓ0 nre ( ^W4) . 0 фе ^ фЬ oJL o

Ί RŤ * '™ е'^{<я / 4} '

For the separation layer with properties we get:

where:

Ei is the electric vector of the input light,

R | l is the reflectance of the separating layer for the radiation component parallel to the plane of incident,

R ± is the reflectance of the separating layer for the radiation component perpendicular to the plane of incidence, δ ₂ is the difference in phase displacement of the separating plate per reflection,

7] 1 is the transmittance of the separating layer for the radiation component parallel to the plane of incidence, the transmittance of the separating layer for the radiation component perpendicular to the incident plane, and δ ' ₂ is the phase shift difference of the separating layer per passage.

For example, if we have in the detection unit 'for the reference beam:

^{! e} r = Ei for the measurement beam

we get for interference field:

e _s - E] _

- i + cos φι + i sin φι + cos φι + i sin φι

After further separation of interfering beams in the detection unit and inclusion of the analyzer (polarized with Jones matt polarization filter)

Jf, = - sin?), Where:

K. is the attenuation coefficient.

010 01

When inserting the polarization filter into the second split beam with Jones matrix: II we get for the light intensity behind the second polarization filter: LJ ^If2 = + cos ^ j).

It can be seen that we received two signals 4 _,, 1 _Рг in the quadrature with full interference (full contrast). These two signals allow the direction of movement of the moving part of the interferometer to be differentiated and are needed to control the return counters, for example when using a laser interferometer for measuring lengths. Similarly, other signals with a phase shift of zero to 360 ° can be obtained.

An exemplary embodiment of a laser interferometer using said method of obtaining the interference field of two light beams is shown in the attached drawing.

The entire laser interferometer consists of the light source A, the first polarizing member B, the interferometer itself formed by the splitting unit C, the retro-reflecting system E, the additional optical members F and the retro-reflecting system D, and further consists of a detection unit K as described below.

The light source A consists of a single-frequency laser from which a beam and beams emerge, linearly polarized in the oscillation plane yz. We consider the orthogonal coordinate system x, y, z, where the z axis is the axis of beam and beam propagation and in the yz plane the plane of incidence of the dividing plate 2 is located. The beam and beams first pass through the first polarizing member B or to form a circularly polarized beam of light, which proceeds further to the splitting unit C. On the approximately non-polarizing splitting layer 1 of the plate 2, the beam and rays are divided into the first reflected beam o. and the first beam of b _{ rays released.

We assume that the separating layer 1. it is so-called non-polarizing, ie it has approximately the same reflectance in the plane of impact R || and perpendicular to it In any case, ^ + ^ = к (т _{1 +} т _п ), where:

k = 1 - Zp in the case that in the interferometer the additional optical elements F are in the path of light transmitted by the separating layer 1;

k = --- case that interferometrujsou přídvvné pptické members (F ') in the light path, ddraeeného ^{_ p} avlicí layer 1;

From _p - loss of optical elements F or F '.

Hereinafter, the beam and the beams are circularly polarized and the separating layer 1 of the plate 2 has a different reflectance for the radiation component thymphoed with the incident impact Ky and the component perpendicular to the plane of incidence and exhibits a phase shift between the two components. Then, after a fixed reflection on the separating layer 1 of the plate 2, the first reflected beam ar is elliptically polarized with the general position of the oscillation plane relative to the plane of incidence

Г1 01

The first reflected beam a ₁ is further reflected by the back reflection system E and passes through the second polarizing member G. The functional property of the second polarizing member G is to rotate the azimuth passing through the first reflected beam. beam _R and 90 °. As a result, the radiation component which lies on the beam and before the first impact on the separating layer 1 in the plane of impact is situated before the second impact on the same separating layer 1 in a plane perpendicular to the plane of impact and vice versa. This double successive reflection on the same separating layer 1 compensates for the reflectance differences in the different planes and subtracts the phase shifts. As a result, the second reflected beam and ₂ beams then have the same polarization form as the original beam and beams. The losses Z _{p of the} additional optical members F are compensated for by the overall higher reflectance (K "4- K _± ) of the separating layer 1. The phase shifts of the retro-reflective system E and the additional optical members F, which are usually small, can be included as a correction in arranging a second polarizing member G.

The first transmitted beam of _x- rays passes through the additional optical members F and is reflected by the retro-reflective system D, passes again through the additional optical members F, further through the third polarizing member H and impinges again on the separating layer 1 of the plate 2. an oscillation plane of elliptically polarized light with a general oscillation plane position of 90 ° and the conversion of the second transmitted beam b ₂ to light linearly polarized with an oscillation plane below 45 ° relative to the plane of incidence of the splitter plate. ₂ and a linearly polarized second transmitted beam b ₂ .

It is assumed that the beam polarization form a _x , b ^ together with the used polarizing members G, ev. H may be swapped together, i.e. the first reflected beam may be linearly polarized and the first released b _r may be circularly polarized.

In some cases, it is preferred that the interferometer itself operates only with orthogonally linearly polarized light beams. Using only orthogonally linearly polarized light beams in interferometer a ₂ , b ₂ , one of the beams is transformed into circularly polarized in the detection unit К, while the other remains linearly polarized. In this case, the interferometer works with orthogonal linearly polarized beams and the conversion to a combination of circular and linearly polarized light is performed after the interferometer in the detection unit K.

Claims (2)

OBJECT OF THE INVENTION 1. A method of generating an interference field of light beams comprising information on the position and sense of relative motion of interfering light beams between each other, characterized in that the interference field is caused by the interference of two light beams, one polarizing linearly and the other circularly or elliptically. 2. A laser interferometer for carrying out the method according to claim 1 with a detecting unit for producing a light beam interference field, characterized in that either in the interferometer or in the detecting unit (K) in the axis of the measurement and reference beams (a _x> bj of light) The beams (a ₂ , b ₂ ) are between the plate (2,2 ') and the additional optical members (F, F') of the second and third polarizing members (G and H; G 'and H'), the second polarizing member (G , G) is formed by a linear delay half-wave plate (21) and a third polarizing member (Η, H ') is formed by a linear delayed quarter wave plate (22) and a linear half-wave delay plate (23).