DE2027983A1 - Procedure for error compensation - Google Patents

Description

IBM Germany Internationale Büro-Maschinen Gesellschaft mbH

Boeblingen, May 29, 1970 pr-ba

Official file number: New registration File number of the applicant: Docket GE 969 016

Procedure for error compensation

The invention relates to a method and an arrangement for error compensation with interferometer !! with oppositely circularly polarized partial bundles and determination of the measurement results Evaluation of the changes in brightness occurring simultaneously in one or more polarization directions.

When lasers are used as light sources for interferometers, the frequency stability of the laser is impaired by the reaction of the light reflected in the interferometer , which can be very disruptive, particularly in the case of long-term measurements and series of measurements, especially when checking the dimensional accuracy of large numbers of semiconductor components o Bs it has been shown that this disturbing reaction to the frequency stability of a laser used as a light source in interferometers ^ especially in Michelson interferons tern, with oppositely circularly polarized partial beams is particularly low. In such an interferometer, two oppositely circularly polarized partial bundles are brought to interference in the combined bundle, whereby a linearly polarized beam is generated.

109861 / 0.6

stands in which the position of its plane of polarization is a function of the phase relationships of the two sub-bundles. will this When combined bundles are viewed through an analyzer, a group of interference fringes becomes visible, which are located at a Shift the relative rotation between the plane of polarization and the direction of transmission of the analyzer. With a very good parallelism of the interferometer mirror, there are no interference fringe displacements but only fluctuations in brightness are visible. Both ways of describing this process are therefore equivalent to. With each shift of the phase of one sub-bundle with respect to the phase of the other sub-bundle by one Hellen length the plane of polarization of the combined beam rotates once through 360 °. The interference fringe field visible behind the analyzer is shifted by two interference fringes or two brightness maxima occur in chronological succession and two brightness minima. If a light-sensitive element is arranged in this area, they give at its output occurring electrical impulses the number of half the wavelengths of the light used to di @ the measuring table is moved. The number of these impulses only indicates the amount but not the direction of this shift. Intended to the direction of the shift is also to be indicated, so two light-sensitive elements and two analyzers must be provided are, the transmission directions include, for example, an angle of 45 °. The number of at the output of a light-sensitive Element occurring electrical impulses gives the amount and the phase relationships of the light-sensitive at the output of both Elements occurring pulse trains the direction of the displacement of the measuring table.

Since the measurement results of an interferometer are caused by thermal influences, by changing the frequency of the light used, and can be influenced by changing the temperature and the pressure of the air located in the course of the beam paths, which This is particularly annoying with longer measurements, a whole series of procedures for correcting the by changing these

109851/0626 Docket GE 969 016

. ■ - 3 - '' ■ ■. ' ■. ■ '■■

Suggested parameter related error. For example Precautions to stabilize the light sources used, for the storage of the mirror which cannot be thermally influenced and beam splitter to hit the interferometer and means for controllable adjustment of the interferometer elements provided by the undesired and disruptive changes in the phase relationships the sub-bundle can be reversed. These measures are very complex on the one hand, and could on the other hand so that the desired goal can only be partially achieved.

However, arrangements have also become known in which the two most important of the above-mentioned influence the measurement accuracy Parameters determined and used as the basis of a correction factor can be used to correct the readings. This process is not only cumbersome and costly but also has the particular when performing longer series of measurements or a very disturbing disadvantage in quality controls, that from the occurrence of a disturbance to its correction a relatively long time elapses in which, under certain circumstances, a large number of incorrect measurement results can be read.

The invention is based on the object, a method and an arrangement for carrying out the method for error compensation in the case of interferometers with oppositely circularly polarized partial bundles, indicate with which the errors that occur in simple terms, very precisely and with a very small time constant automatically compensated.

This object is achieved according to the invention by a method for Error compensation in interferometers with opposite directions circular polarized partial bundles and determination of the measurement results by evaluating the polarization in one or more directions of polarization of the combined bundle simultaneously occurring changes in brightness, which is characterized in that the changes changes in brightness that occur due to the environmental conditions either by a comparison interferometer or by measuring instru-

10 9 8 5 1/0626 Docket GE 969 016

ments and calculation are determined and converted into a control variable, which at the ^{interferometer to be kotapensier c} ends the polarization direction or Poiarisatioasrichtragen j, under which the combined bundle is evaluated, rotates together so that the brightness changes that have occurred are reversed.

A particularly advantageous development of the inventive concept. kens is characterized in that the angle between the evaluated polarization directions of the combined bundle is less than 90 °, preferably equal to 45 ° »

Another, particularly advantageous fJeiterbiletaag of the invention Method is characterized in that the values for the rotation of the polarization directions causing the error compensation from a second similar interferometer, taking into account the difference in length can be derived.

Another particularly advantageous further development of the method according to the invention is characterized ₉ characterized in that the measuring section of the Vergleichsinterferometers limiting mirror is arranged on an element dependent on an applied voltage curve, that the element or another element zn periodic oscillations with an amplitude in the size a quarter wavelength of the partial bundle is excited so that as a result of this movement fluctuations in the light intensity of the combined bundle around a minimum value or a maximum value, a control voltage determining the length of the element carrying this mirror is derived to symmetrize the position of said minimum or maximum values that this control voltage is also fed to a voltage divider which has a fixed center tap and a tap which can be moved together with the measuring table of the measuring interferometer and which is used for one of the path length difference. Zero of the measuring interferometer corresponding position of the measuring table in the middle of the voltage divider. stands, and that at the fixed center tap and the

109851/0626 Docket GE 969 016

shiftable tap occurring botential change the direction and the amount of mutual rotation of the polarization directions defined in which the combined beam of the measuring interferometer is evaluated.

Further characteristics of the invention emerge from the sub-. Sayings.

The invention will then be explained in more detail with reference to the figures. Show it:

1 shows the schematic representation of an arrangement

with two interferometers - for * explanation * d @ s

Inventive idea;

Fig. 2 ■ a schematic representation of the

of a photosensitive element occurring -

■ Waveforms and the waveforms of a one

■ piezoelectric element stimulating high-frequency voltage source; '

Fig. 3. the schematic representation of an A ^ sfühniftgs-

form of invention.

The arrangement shown in Fig. 1 consists of a comparison interferometer, a measuring interferometer and the necessary elements for compensation of the measuring interferometer , while 'ren part of the figure shown interferometer includes the numerals 11, 13, 17 and 18 designated elements.

A linearly polarized light beam emanating from a laser 1 2. When it passes through a λ / 4 plate -3 in a circularly polarized beam converted into a »beam splitter 4 in a vertically upward partial beam 2f and

109851/0626

Docket GE 969 016

202798

Kiv? "':

a partial beam 2a running to the right. The beam splitter 4 consists of a larger I thin, alternately each different refractive-pointing dielectric layers and is so au; g; w; '.--- ■ ■ -.- b the polarization of the penetrating ray and of the ^ i l- \ ■ "> -flexed ray""is not changed« The u & a-l zs-ti- ■■ · .-? νΐί running partial beam 2a is in the same direction-v;: r .; v \ ·; ■ ;;.:, · .; 3 2 circularly polarized and reaches the radiation !; -.; _: -, £ : r in the same way as the beam splitter 4 a;: -; ?. " .. - ~ '& At this beam splitter is © in part of the stra?' ..: ■■ - ^- · '.-- "...':>, - anach above as beam 2c reflected and fei .-: '--.-. " ... """■ -

w let through undistracted »The rt- - ■" ■■■ - - - ^:. " polarized beam 2b is aa a mirror 8: ■ ..: ".. ■""" - ': ■:;. arrives back in the same way. ".,". -which it partly as ray 2r u &<sh laat ^ n reflei = '"''." ■■ -: Ά se in the direction of the originally- © iafsliendea Str ^f - ■ -. '. '■. --- i ™ let «The beam at the beam splitter 5 aaeh above r -: '■■" ■ ■■. "-' ^r beam 2c penetrates a / ^^ plate β _v which he L ·: ■; - ■ - '. ^: ..- slertsr beam leaves ^ is aa a mirror 7 r- ■ - "■ -""- ■ -. äörcfesiätafe <Mm χ / 4 plate β © ia second time ₁₇ woL--""■'- .. ". ; is ularly polarized »This implies the ssueimf · '· ■'. ■.: ■ '-.- .; by the λ / 4-plate β the «rspraglieh rec- ■; \ ^-..-,::: ■ τ * risierte linksgisfaalar pe feiistrahl 2º in-one ":, i - &'■■' ■ uiigewaßdelt 21, äex AEEN beam splitter 5 © toa JFE" - - ■■■ - ^ i: -? RisatioBsrastendes äörehsetat and as with aera S * '-: - ^v , - render beam scm delivery receiver 20 arrives _o Da: - ■ "■'" inflected, right circularly polarized © - part tr. . ^; - ■ - <■ keiae λ / 4 plate, s © that it is larized -sowoSni after the Hai ■ ■; -as also after the reflection sm ray © at © il @ r S - ■ and alg stra £ l 2s gram Lidhtdsapf am - "the co-operation of two mutually sensual sirkulai - - rays result in a © linearly polarized © S tr al- - ■■ ■; ■: - position of the polarization plane © © in © FunJcti © n der Wf . . -. - - - ■■■: ■: ■■ ' between dea right ^ irkalgr and ä @ a
Teilstrahien 2r raad 21 isto Hiatss @
Schar ¥ on iaterferanzstreifeii "di © see bsi ÄadssrisE- ■ - da ;, ..-,., -

10S851 / 0626 'Docket GE 969 016

between

polar is ie-,
fangers 2C

Interfer - "

on sin Il

circularly polarized and the right circular ..beam over the receiving surface of the light emitter

sn. As already mentioned, very carefully there are no erferometers behind the analyzer

but changes in brightness, but that 'xiches element have the same effects.

'© tu .-,. * Sr 4 penetrating partial beam 2f becomes, of χ * c; 11, who in the same way as the rays

interspersed ι * al still near ¹ - Oil ^ thing-j. durc * ' is ier oil J 'r- ^ kular polci "ν Ϊ tierbe Tel ι. Τ enforced ο «N Sl

A can Sieines Strar

divider .4 vn b al b <- u »i3 is partially transmitted as partial beam 2g IK - t" *: i reflected as partial beam 2h to the right and is clicked on a mirror "7", after which he uses the λ / 4 plate 13 again _:

* ilbeam 2i to the left towards a

eibende arrangement 30 is reflected. At ¹ laligen passage through the ./4 plate 13 ..- eiler 11 reflected partial beam 2k left-circulating

r on the beam splitter 11 to the right reflec ~. is reflected at a mirror 18 "and." Si * α-enteiler 11 as. Right circularly polarized partial beam 2i, due to the interference between two oppositely circularly polarized beams 2i and 2k occurring in the area of the arrangement 30, a. linearly polarized ■ beam in which the position of the plane of polarization is a function of the phase difference between the two partial beams. It should be pointed out that, given the position of the mirror, the one in the upper part of Fig. 1 shown measuring interferometer the. Has a path length! Fference Hull.

The mirror 8 is attached to a piezoelectric element 9, which in turn is arranged on a piezoelectric element 10. The piezoelectric element 9 is connected via lines 41 and 42 allow the AC voltage source 24 to be in the range of a few KHz vibrations. The AC voltage source 24 is also connected via line 43 to the input of a phase-sensitive rectifier 21, whose

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The second input is connected to the output of the light-sensitive element 20 via the line 35. The phase sensitive Rectifier, 21 is connected via a line 34 to an integrator 22, which is connected to an amplifier 23 via a line 33 connected is. The output of the amplifier 23 is via lines 32 and 35 to the piezoelectric element 10 and via a Line 36 connected to one side of a voltage divider 37, whose other input is grounded. The sliding contact 39 of this voltage divider is with a reflective surface 18 supporting measuring table of the measuring interferometer shown in the upper part of FIG. 1 rigidly connected so that it is simultaneously with this is moved. A center tap of the voltage divider 37 and the sliding contact 39 are connected to the lines 38 and 40, Via which the correction voltage required to control the arrangement 30 is transmitted.

The piezoelectric element 9 connected to the AC voltage source 24 via the lines 41 and 42 moves the mirror 8 by about a quarter wavelength in the direction of beam 2b. This is between the right circularly polarized and left circularly polarized rays 2r and 21 generates a phase difference that causes a rotation of the plane of polarization of the through the interference of the two beams results in linearly polarized light. As already mentioned, when turning of the plane of polarization of the light fed to the analyzer P, the array of interference fringes arising at the output of this analyzer Moved over the photosensitive element 20, so that a series of pulses arise at the output, whose Frequency equal to the oscillation frequency of the piezoelectric Elements 9 is. As already said, the one output of the alternating voltage source 24 is via the line 43 with one Input and output of the light-sensitive element 20 via the line 35 to the other input of the differential amplifier trained phase-sensitive rectifier 21 connected. The phase positions of the transmitted via lines 35 and 43 Signals are derived from the scheme shown in FIG.

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table representation. The upper curve described by the coordinates V and t represents the curve at the output of the Light-sensitive element 20 occurring signals, which are a function of the brightness fluctuation occurring at the input of this element is. The curve shape reproduced by the coordinates V and t represents the signals transmitted via the line 43. The arrangement is such that when they coincide the zero crossings 50 and 51 of the upper and lower curves at the output of the phase-dependent rectifier 21 a signal with the amplitude zero occurs »If the zero crossing falls 50 of the upper curve shown in FIG. 2 with a positive value that in the lower part of that shown in FIG Signal curve together, it arises at the output of the phase-sensitive Rectifier 21 has a positive signal, the amplitude of which depends on the difference between the potential applied to the arrangement d. H. depends on the mutual displacement of the two curves. If the zero crossing 50 falls in time with a negative The value of the curve shown in the lower part of FIG. 2 together is produced at the output of the phase-sensitive rectifier 21 a negative signal which corresponds to the negative voltage of the voltage across line 43 transmitted signal is proportional. The one at the output of the phase sensitive Rectifier 21 occurring signals are transmitted via line 34 to the integrator 22, the output of which via the line 33 is fed to the amplifier 23. The output of the amplifier 23 is via the lines 32 and 35 with the piezoelectric element 10 connected. Reinforcement of the arrangement 23 is dimensioned so that when the wave train shown in the upper part of FIG. 2 is shifted to the right, a Extension of the piezoelectric element 10 is effected so that the zero crossings of the in the upper and lower part of the 2 coincide again. In the same way, with a shift to the left, the voltage curves shown in the upper part of FIG. 2 at the output of the amplifier 23 generates a voltage which shortens the piezoelectric element, so that the zero crossings of the two in

1098517 0826. Docket GE 969 016

-.10 -

2 coincide again. If the temperature and / or the barometric pressure of the space surrounding the interferometer changes in the course of a series of measurements, this is also associated with a change in the dielectric constant of the air through which the partial bundles of the interferometer pass. A change in the relative positions between the individual mirrors cannot be ruled out either. If the change in dielectric constant, for example, in a sol = ciien direction so that thereby an enlargement of the wavelength is connected to "the sub-beams, as is done because of the interferometers shown in the lower portion of FIG. 1 having a different Hull path length _f is a displacement of the Interference fringes occurring in the area of the light-sensitive element 20. As already mentioned, these interfering fringes a are periodically displaced by about half a fringe spacing "ad h @ r" under the effect of the mirror 8, which is periodically shifted by the piezoelectric element 9 in the direction of the beam 2b, so that a This strip is shifted in position, for example, a lateral shift in the changes in the I3 @ li ± ability to a time shift in the zero crossing of the electrical signals occurring at the output of the light-sensitive element 20 and fed to the phase-sensitive rectifier 21 via the conductor 35. As described above., leads to a phase shift between the signals transmitted via line 35 and via line 43. to an electrical controlled variable which causes a length extension of the piezoelectric element 10 that reverses this phase shift. This controlled variable is a function of the change in the dielectric constant of the sub-bundles air permeated by the interferometer. It can be seen without further ado that if this dielectric constant changes, one - the -. The size of the change is proportional to the change in the wavelength of the partial beams of the interferometer. The greater the wavelength of the partial beams of the interferometer, the greater the change in length of the piezoelectric lament 35 and 43 transmitted electrical

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Signals should be avoided or reversed. It is furthermore without further ado that this is at the output of the amplifier 23 occurring signal is proportional to the change in dielectric constant of the air penetrated by the partial beams. The control voltage appearing at the output of the amplifier 23 is also fed to the one input of the voltage divider via the line 36 37 transmitted, the other input of which is grounded. The sliding contact 39 of this voltage divider is mechanically connected to the measuring table having the reflecting surface 18 in the upper part of the Fig. 1 connected interferometer, so that in the drawn Position between the line 38 connected to the center of the voltage divider 37 and that with the sliding contact 39 connected line 40 is no voltage difference.

In the position shown in the upper part of Fig. Interferometer shown has a path length difference equal to zero, so that changes in the dielectric constant of the sub-bundles permeated air have no influence on the measurement result. In this position of the measuring table is therefore independent of the The control voltage transmitted via the line 36 does not transmit any correction voltage via the lines 38 and 40. Will be the measuring table with the reflecting surface 18 shifted to the left or to the right, the results in the beam path in the upper area the measuring interferometer shown in Fig. 1 is a non-zero Path length difference, so that a change in wavelength the partial beams result in a phase shift that falsifies the measurement results. In such a position of the measuring table the sliding contact 39 firmly connected to this is no longer in the center of the voltage divider 37, so that a change in the control voltage transmitted via the line 36 a change in the difference between the potentials of the Lines 38 and 40 result. As is readily apparent, the size of this potential difference is a function of the position of the sliding contact 39 and the size of the control voltage transmitted via the line 36. Because the size of this control voltage

109 851/0626 Docket GE 969 016

a puncture of the one present in the area of both interferometers Is a parameter, the difference between the potentials on lines 38 and 40 is also a function of these parameters. Will lines 38 and 40, for example, with a moving coil instrument or another suitable drive element, its deflection is also a function of the above-mentioned Parameter. This drive element adjusts the arrangement 30 to be described in more detail in such a way that the change the above parameters, namely the temperature and the air pressure, resulting falsification of the measurement results is reversed.

In FIG. 3, an exemplary embodiment of the one designated by 30 in FIG. 1 is shown Arrangement reproduced.

The components identified in FIG. 1 2i and 2k are incident on a lens 52, it is split in a beam splitter 53 into two beams 54 and 55 exit as converged beam. The two partial beams pass through analyzers 56 and 57 and arrive at light-sensitive elements 58 and 59. The analyzers 56 and 57, the directions of which pass through an angle of 45 °, are fastened in toothed rims 60 and 61, which mesh with a toothed wheel 62 common to them , which is driven via an axis 65 by a moving coil instrument 66. Since the numbers of teeth of the ring gears 60 and 61 are equal to one another, when the gear wheel 62 rotates, the analyzers 56 and 57 are rotated in such a way that their passage directions always include the same angle with one another. If the control voltage on the line 36 is zero or if the measuring table of the interferometer shown in the upper part of FIG. 1 is in the position shown, there is no voltage at the terminals 67 and 68 of the moving coil element 66 and the gear 62 does not rotate. However, if the reflective surface 18 of the measuring table and thus also the sliding contact 39 are in a position other than that shown in FIG. 1, and the dielectric constant changes due to the partial beams of the two interferometers

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Docket GE 969 016

permeated air, the control voltage transmitted via the line 36 increases, which results in a potential difference, referred to as the correction voltage, between the lines 38 and 40. The control voltage acting on the piezoelectric element 10 via the lines 32 and 35 has the consequence that in the interferometer shown in the lower part of FIG. In the measuring interferometer shown in the upper part of FIG. 1, however, the interference fringes occurring in the area of the arrangement 30 are shifted, provided that the path length difference of this interferometer is different from zero, so that a series of light pulses occurs in the area of the light-sensitive elements 58 and 53 which are transmitted to an evaluation unit 73 via lines 70 and 71. With unchanged temperature and with unchanged pressure, there is a clear relationship between the displacement of the reflective surface 18 of the measuring table and the displacement of the interference fringes in the area of the light-sensitive elements 58 and 59, which by the evaluation unit 73 in a clear statement about the amount and direction of the Displacement of said surface 18 is converted. If the temperature and / or the air pressure were to change in the area of the measuring interferometer shown in the upper part of FIG. 1, the interference fringes would shift in the area of the light-sensitive elements 58 and 59, which would lead to a falsification of the measurement results. Since a change in temperature and air pressure is also effective in the area of the second interferometer shown in FIG. 1, a control voltage is produced on line 36, as described above. The control voltage transmitted via the line 36 is a function of the environmental changes _r occurring in the area of both interferometers, which falsify the measurement results of the measuring interferometer. The control voltage generated as a function of said control voltage and the position of the measuring table having the reflecting surface 18, which is fed to the moving-coil instrument 66 via the terminals 67 and 68, causes

109 85 1/0626 Docket GE 969 016

that the analyzer ^ »5β and 57 are rotated continuously so that no shift of the interference fringes in the light-sensitive area due to a change in environmental conditions Elements 58 and 59 occurs so that the change the falsification of the measurement resulting from the conditions of the Ulm world results is compensated.

In the following are the effective x-grounding physical Regularities briefly explained again

P If two oppositely circularly polarized, coherent light beams are brought to interference, a linearly polarized light beam is created. The position of the plane of polarization this Beam of light is a function of the Phassama difference between the left circularly polarized and the right circularly polarized Ray »becomes the phase position of the interfering Rays either by changing the position of the individual elements of the interferometer or by changing the wavelengths, der teiefea Liehtstralilen iferäadert ^ so you see it Plane of polarization of the by the interference of both against = meaningfully circularly polarized rays »If the now linearly polarized light beam is an analogue

If the analyzer is arranged, interference = -, stripes or, in the case of an ideally adjusted interferometer, a certain brightness value are visible. These later ^ stripes or brightness values shift or change ^ 'if the transmission direction of the analyzer is changed in relation to the lag® of the plane of polarization of the light beam introduced to it

1. When carrying out a measurement, the one arranged on the measuring table is used reflecting surface 18 shifted.

2. The wavelength of the beam supplied to the laterferometer is, for example, a change in the refractive index

109851/0626 Docket GE 969 016

and the temperature of the air.

3. The relative position of the transmission direction of the analyzer and the plane of polarization of the linearly polarized one fed to it The beam is changed by rotating the analyzer.

The amplifier 23, the voltage divider 37, the moving coil instrument 66 and the transmission ratio of the gear 62 with respect to the ring gears 60 and 61 are dimensioned so that the over the lines 32 and 35 transferred to the piezoelectric element, one Interlocking the phase relationships of the signals transmitted via lines 35 and 43 causing control voltage at the same time such rotation of the moving coil instrument 66 and thus the analyzers 56 and 57 causes a change in the Environmental conditions caused the interference fringes to shift in the area of the light-sensitive elements 58 and 33 reversed is made. Compensation for changes in environmental conditions Any measurement errors that arise could also be carried out with a single rotatable polarizer. But because of the As is known, displacement of a single interference fringe field is only the amount but not the direction of a change in length can be determined, two polarizers are provided, the transmission directions include an angle of 45 ° and which generate two phase-shifted interference fields in the area of the light-sensitive elements 58 and 59.

109851/0626

Claims (5)

- 16 - smells Procedure for error compensation in interferometers !! with oppositely circularly polarized partial bundles and determination the measurement results by evaluating the one or more polarization directions of the combined Bundle of simultaneously occurring changes in brightness, fe characterized in that the changes in brightness occurring with changes in environmental conditions either determined by a comparison interferometer or by measuring instruments and calculation and converted into a controlled variable are converted, which in the interferometer to be compensated the polarization direction or polarization directions under which the combined beam is evaluated is, rotates together so that the changes in brightness that occur with changes in environmental conditions To be undone. 2. The method according to claim 1, characterized in that the angle between the evaluated polarization direction r directions of the combined bundle less than 90 °, prefer wise equals 45 °. 3. The method according to claims 1 and 2, characterized in that the values for the error compensation causing rotation of the directions of polarization of one second similar interferometer can be derived taking into account the difference in the measurement lengths. 4. The method according to claims 1 to 3, characterized in that a measuring section of the comparison interferometer limiting mirror (8) is arranged on an element (10) with a position dependent on an applied voltage, that this element or another element 109851/0626
Docket GE 969 016 - (9) the partial bundle is excited to periodic oscillations with an amplitude of the size of a quarter wavelength that occurs as a result of this movement Fluctuations in the light intensity in a region of the combined beam around a minimum value or a maximum value of a control voltage determining the position of the element carrying this mirror for balancing the position of said minimum or maximum values is derived that this control voltage also a Voltage divider (37) is fed / which has a fixed center tap and one with a mirror surface (18) provided measuring table of the measuring interferometer jointly displaceable tap (39), which at one of the Path length difference zero of the measuring interferometer corresponding position of the measuring table in the middle of the voltage divider stands, and that the change in potential occurring at the fixed center tap and the displaceable tap defines the direction and the amount of common rotation of the polarization directions in which the combined beam of the measuring interferometer is evaluated. 5. Arrangement for performing the method according to the claims 1 to 4, characterized by a beam splitter (53) for splitting the from a right circular and a left-circularly polarized partial bundle (2i, 2k) resulting combined bundle of a measuring interferometer, by two jointly rotatably arranged in the course of the partial beams emerging from the beam splitter Analyzers (56, 57), the directions of rotation of which enclose an angle different from 90 °, through both Analyzers jointly moving drive elements (62, 65, 66), which by means of a comparison interferometer or controlled variables generated by means of suitable measuring devices in a possibly occurring measurement error compensating Dre ^, of the analyzers (= 56.5?) and thru the Covers ft 96t Light-sensitive analyzers (56, 57) connected downstream Elements (58, 59) for determining the changes in brightness occurring in their area, indicating the measurement result. Arrangement for carrying out the method according to the claims 1 to 4, characterized by a light source (1) for generating a linearly polarized light beam (2), a λ / 4 plate (3) for converting the linearly polarized 'Light beam (2) into a circularly polarized Light beam, a first beam splitter (4) for splitting the light beam into a comparative gas interferometer (5, 6, 7, 8) to be fed light beam (2a) and a measuring interferometer (11, 13, 17, 18) to be fed Light beam (2f), a mirror (8) of the comparison interferometer carrying first piezoelectric element (9) for periodic displacement of the mirror (8) by about a quarter of the wavelength of light the light source (1), a second piezoelectric element (9) carrying the mirror carrying the piezoelectric Element (10) one at the output of the comparison interferometer arranged analyzer (P) and a light-sensitive element arranged behind it (? ©> to determine the changes in brightness occurring in its area, means (21, 22, 23) for generating the> "^ Occurrence of changes in brightness at the lic | ^ ej ^ sensitive Element (20) by acting on the piezoelectric Element (10) reversing correction signal at the same time an arrangement (3O> is fed to the measuring interferometer :. origina imspected IiIIIIlIIItI.