DE2353108A1 - MEASURING ARRANGEMENT FOR MEASURING PHASE SHIFTS - Google Patents

Description

■ —.-- - · ■■■ ... 410-21.

Cr .- '. No. . · ;. ac t_ i * - jr.

B Munich 22. Sle'.ncdorfstr. 10

23rd October 1975

Commissariat ä 1 'Energie Atomique Paris (France)

Measuring arrangement "for measuring phase shifts

The invention relates to a measuring arrangement for Measuring the phase shift caused by a system for phase shifting electromagnetic radiation

The measuring arrangement designed according to the invention are available numerous applications are open, of which only measurement in particular the electron density in a plasma, the measurement of 'refractive indices, the measurement of changes in the dimensions of mechanical components and measurements in the meteorological field as examples be called '. ·

It has already been suggested that the actions one radiation when it passes through a phase-shifting system or when it comes into contact with such a system

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System learns with the help of interferometric methods to eat. These methods have been used in particular in the investigation of plasmas. she generally work with an incident wave supplied by, for example, a laser, which is divided into two Partial waves are split with the same frequency, one of which is the one with the passage through the Plasma related effects is exposed, while the other experiences no change and therefore as Reference shaft can serve. Examples of interferometric Devices that are used to carry out these procedures can be found in U.S. Patents 3,510,665 and 3 539 262. In these known arrangements, the incident waves originating from a laser can be contain two different frequencies that are coupled with two different oscillation modes in the laser, however, these frequencies both traverse the plasma. These known methods and arrangements However, the accuracy required for certain measurements is lacking.

To enlarge the arrangements known with these achievable accuracy has already been proposed, the reference beam · for example with the help of a Periodically deflect the pendulum motion executing mirror and a Fourier analysis for the on the interferometer perform the transferred service; from this one can then use one of the two partial waves in the ' Interferometer derive phase shift experienced. Regarding the details of this mode of operation on one of JrN. Olsen under the title Fractional Fringe HCN Laser Interferometer "in" The Review

of Scientific Instruments "," Volume 42, Number 1, January 1971 » Page 104, published article will. However, this procedure is because of the detected signal to be carried out Fourier analysis in its implementation very complicated.

The invention is therefore based on the object of a To train the measuring arrangement of the type mentioned in such a way that it can be used while avoiding those described above Disadvantages "of the known methods and arrangements Phase shift on an electromagnetic wave caused by a phase shift system to be measured with high accuracy and in a simple manner.

This object is achieved according to the invention in that the measuring arrangement has a source for electromagnetic radiation which emits a wave of the form χ = a cos wt, a beam splitter fed with this time, which splits the wave fed to it into two partial waves, a rotating cylindrical diffraction grating , to which one of these partial waves is fed and which shifts the frequency of this partial wave by an amount w '- w = (v / c) w, where c is the speed of light and ν is the component of the linear grating speed along the direction of the Wave stand at their point of impact, a system for phase shifting arranged on the path of one of the two partial waves, which shifts the phase of the wave fed to it by the value ^ , a union element to recombine the two partial waves, which are mutually shifted in frequency and phase, 'a first not fed with the beam emitted by this union member

0.8.1-9 / 10-3-3.

linear detector which emits a low-frequency electrical signal ζ = c cos I (w '- w) t - fj and has a device connected to the output of this detector for measuring the phase shift -f contained in this low-frequency electrical signal. . .

The basic principle of the invention consists in the phase shift that is to be measured and the affects a very high frequency wave, converting it to a low frequency signal by acting as a reference wave a wave is used whose frequency is slightly shifted from that of the incident wave is. The beats between these two waves, which are mutually offset in phase and frequency, deliver then a low-frequency signal that contains the information to be measured, namely the phase shift of interest * the measurement of this variable can then be carried out however, make it with high accuracy, since the phase shift of interest occurs in this case affects a low frequency signal.

There are already devices known that a part of systems in the manner of an interferometer and the frequency of a wave using the Doppler effect move. The simplest device of this type works with a uniform movement of one of the Mirror that forms the end of one arm of the corresponding interferometer. Regarding the details the construction and operation of such a device can be based on one of R.W. Peterson under the title "A far-infrared coupled-cavity interferometer "in the journal" Applied Physics Letters ", Volume 18, Number 10, May 15, 1971,

^ 09019/1033

Page 14O, published article may be referred to. The operation of such an interferometer is based essentially due to a variation in the length of one arm of this interferometer. Therefore it is not suitable for permanent measurements or for long-term measurements, as the mirrors are not displaced infinitely can. In the article cited above, a device is further described which has a rotating mirror contains. However, this device can also not be used in Work permanently, but only during the short time intervals in which the mirror is a suitable length In relation to the arm of the interferometer.

Next is aiming the frequency of a wave by means of the Doppler effect, and always for use in devices for overlay testing it has been proposed to use a spreader wheel. Regarding the details of this method can on one of M.C. Pond and others under the title "Optimum Heterodyjne detection at 10.6 / Um in photoconductive Ge; Cu "in the Zettschrift Applied Physics Letters, Volume 9, Number 10, I5.II.I966, page 357 In these devices, however, the scattered and the frequency drops postponed performance is very low; are said to be the original source of energy using hydrocyanic acid lasers (HCN lasers) are used whose emission power is inherently very small, then it is necessary to use detectors of very complicated design and difficult to use expose yourself.

The inventive use of a rotating diffraction grating provides a means to the hand that better meets the various demands of practice

"4QS819 / 1033 *

is fair than the previously known devices for the same purpose and in particular at a 'high Efficiency leads, with no change in the length of the Interferometerarraes, in whose train the diffraction grating inserted is required.

Advantageous embodiments and. Advanced training of the invention are detailed in the subclaims marked.

For the further explanation of the invention and its advantages, reference is now made to the drawing, illustrated in the preferred exemplary embodiments for a measuring arrangement designed according to the invention are; show in the drawing:

Fig. 1 is an overall diagram for the construction of a measuring arrangement designed according to the invention;

Fig. 2 shows a first variant embodiment for a

measuring arrangement designed according to the invention, which is inserted into an interferometer;

3 shows a graphic representation to illustrate the parameters and the behavior, one that works in autocollimation and is designed as an echelette grating Diffraction grating;

4 shows a graphic representation to illustrate the measuring principle for measuring the phase shift -f on a low-frequency wave;

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ORiaiNAL INSPECTEÖ

Fig. 5 shows two design variants for an electronic circuit for measuring the Phase shift ^ and

6 shows a second embodiment variant for the construction of an interferometer with one designed according to the invention. Measuring arrangement. ".." ■ - .. "·. ~. \ ~

In the overall representation of FIG. 1, a radiation source 2 emits radiation "4, the shape of which satisfies the formula χ = a cos wt, where a denotes the amplitude of the field assigned to the wave and w its angular frequency split into two partial waves 8 and 10 'One of these two partial waves, for example partial wave 10, passes through a device 12 which emits a wave 14 of the form y = b cos w't shifted in frequency passes through a milieu remit "phase shift, from which a wave 18 of the form u = c ¹ cos (w't + ^ ) emerges. Behind the medium 16 combines an optical device 20 to the beam combining shaft l8 with the remaining unchanged part of shaft 8 into a single beam 22 to a detector ₂₄ of nonlinear type is supplied. A circuit 26 for processing the signal captured by the detector 24 is connected to the output of the detector 24.

The radiation source 2 can advantageously be a hydrogen cyanide Be an acid laser that emits radiation with a wavelength of 337 / U. ·

The mode of operation of the arrangement shown in FIG. 1 is structured in the following way.... _

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The detector 24, which on the one hand receives the wave 18 of the form x "= a" cos (w't + 4 ) and on the other hand is fed with the partial wave 8 of the form x ¹ = a 'cos wt, in turn generates a signal the shape:

OO

(x "+ x ¹ ) ² = - ^ - ± ^ I- + a '. a" cos £ (w'-w) t - f J.

The frequency-dependent component contained in this signal can easily be eliminated. The low-frequency component also present contains the phase shift -f to be measured. The measurement of this phase shift ψ is very simple, since it relates to a wave of lower frequency (w ^f - w) and no longer to the original high frequency wave 18 of the form cos (w 't + -f). The phase shift f is measured in circuit 26 in the manner explained in detail below.

The milieu 16 with phase shift can in the arrangement of FIG. 1 instead of in the path of the wave 1Λ without further can also be inserted into the path of the partial shaft 8 without affecting the working principle of the measuring arrangement something changes. The device 12 can also be used for frequency shifting according to the milieu 16 with phase shifting to be ordered.

The entire arrangement can advantageously have the general form of an interferometer, as shown in FIG is where the device 12 for frequency shifting is designed, for example, as a rotating diffraction grating is. -

In the illustration in Fig. 2, the incident wave comes from 409819/1033

In the form of a radiation 4, in turn, from a radiation source 2. A semitransparent plate 30 inserted in the path of the radiation 4 allows two partial waves 32 and 34 to arise from this radiation 4. The partial wave 34 is bent at a diffraction grating 36 of cylindrical design, which in Pig. 2 is illustrated by a circle. The diffraction grating J> 6 is set in rotation about its axis via a motor 38 fed by a current source 40. The partial wave 34 is deflected by 180 ° at the diffraction grating 36 and is then "reflected on the semitransparent plate 30 in the direction of a non-linear receiver. at which it experiences a total reflection, by means of which it is sent a second time through the medium 16, whereby it experiences a phase shift -f due to the double passage through the medium 16.

A second semitransparent plate 50 is shown in dash-dotted lines in FIG Part of the wave coming from the diffraction grating 36. The detector 54 therefore emits a low-frequency signal of the form z ¹ = d cos (w ^T - w) t _: in that the phase shift ^ is not included, since none of the detector 54 The partial beams reaching the phase shifted through the milieu 16. The receiver 42, on the other hand, emits a signal ζ in accordance with the description above, which contains the phase shift -F and has the form ζ = c cos £ w '- w) t - f J. These two signals, and z '

. 409 819/10 33

are fed from the receiver 42 or from the detector 54 to the circuit 26. In the practical embodiment , the interferometer shown in FIG. 2 is brought slightly out of alignment in order to avoid that the partial wave 32 can reach the detector 54 after its reflection on the deflecting mirror 44 and on the semitransparent plate 30, and in this way a deflected beam 33 Such a type of setting of an interferometer is common in the field of interferometric measurements and well known to the person skilled in the art.

In a preferred embodiment of the invention, as will be shown, the combination is the semitransparent plate 50, the deflecting mirror 52 and detector 54 unnecessary; these components are therefore in the illustration in FIG. 2 all only contained in dash-dotted lines. .

Visually, the way of working is similar to that of Jn Fig. 2 shows the arrangement of the method of operation of the measuring arrangement according to 'described above in connection with Fig. Fig.l. In addition, however, the illustration in FIG recognize the advantage that results from the use provided according to the invention in rotation about its axis offset diffraction grating 36 results. If one denotes with W the angular velocity for the rotation of the diffraction grating 36 about its axis and the radius of the diffraction grating 36 with R, the linear speed is calculated V at the periphery of the diffraction grating 36 to V = WR. If the partial wave 34 falls at an angle of incidence i the diffraction grating 36, so the component is calculated the linear velocity V of the diffraction grating 36 along the direction of the partial wave 34 to ν = V sin i. the

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Frequency shift due to the Doppler effect for the partial wave J> k with the angular frequency w then results in (v / c) w, where c denotes the speed of light. This phase shift can be set to any desired value under the influence of the current source which determines the speed of the motor 38 for driving the diffraction grating 36.

Next, consider the properties of one in autocollimation described diffraction grating can be recalled. It is clear, however, that this Type of triggering the frequency shift by means of the Doppler effect has an individual degree of efficiency - that of the diffraction grating used for diffraction. Order - results in and no modification in length of the interferometer arm. Also is obviously, - that the measuring arrangement is constantly in operation ' can be, -as the diffraction grating in the course of its rotation around its axis is constantly able to Partial wave 34 to return to itself Ifcktiereii, .. what of course, this cannot be the case with a rotating mirror. . ;

Let us now briefly recall the functional principle of a diffraction grating operated in autocollimation. For this purpose, in the upper half of a 3 shows the customarily, as an incident beam 60 specifies 62 parameters used for the Besehreibung .Beugung to a grid, In this illustration is the _v normal to the Beugungsgitter62 at the impingement of the beam 60 denoted by N ,. The angle of incidence for the beam 60 with respect to this normal N, has the reference symbol, i, and the angle of diffraction is denoted by r. For a little one

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Area around the point of impact of the beam 6o can the grid 62, regardless of its generally cylindrical configuration, can be regarded as flat, so d aß with the usual formula for diffraction gratings, namely:

m / L = d (sin i + sin r)

can be worked, in which d is the step size of the diffraction grating, m the order for the diffraction under consideration and A denotes the wavelength of the incident radiation.

If the incident beam 60 from the diffraction grating '62 thrown back into itself, so the angle of incidence i and the angle of diffraction become equal to each other, see above If the diffraction grating 62 behaves like a reflector in this regard, one speaks of reflection to Littrow. This autocollimation takes place in of order.1 if the relationship exists between the wavelength Λ and the angle of incidence i;

Λ = 2d sin i '

Part of the incident radiation is not absorbed reflected back, but is lost as diffraction of a different order than 1, which is particularly due to the diffraction beam the order m = 0 applies, to which the so-called mirror reflection corresponds. Let these losses however, as is known, decrease in that suitable values for the step size of the diffraction grating and suitable forms for its öttfufen can be selected. In particular it is according to the representation in the lower half b of Fig.3 of advantage, the angle θ of the

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Facets of the diffraction grating opposite the tangent to the diffraction grating, the so-called angle of attack, to give the size of the angle of incidence i to that given off for the first order diffraction spectrum Bringing intensity to its maximum value.

You can also use the step size d for the diffraction grating choose so that the following condition is met:

It can be shown that under these conditions the only solutions to the lattice equation for m = O. and can be obtained for m = 1; thus only the diffraction orders 1 and O exist, which results in the losses decrease accordingly.

In an exemplary embodiment built by the applicant for operation with a wavelength of 337 yes , the diffraction grating was designed as an echelette grating and had a total of 3600 steps, i.e. 10 steps or teeth per degree of angle , Cut into metal disc. The percentage of self-reflected radiation intensity was greater than $ 80.

The structure shown in FIG. 2 is not the only possible one. Within the scope of the invention, an interferometer of the Mach-Zehnder design can also be used, which has two offset arms. For the acceptance of a reference signal of the form z ¹ ■ = d cos (w '- w) t is then a

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to add a second detector that covers part of the V / ellen before and after the frequency shift receives fed. This second variant of the invention is illustrated in FIG.

In the illustration in FIG. 6, components that are also present in the embodiment according to FIG. 2 have the same reference numbers as there. In the exemplary embodiment according to FIG. 6, a first semitransparent plate 100 divides the incident radiation 4 supplied by a radiation source 2 into two partial waves 8 and 10. The partial wave 8 passes through a milieu 16 with a phase shift, where it experiences a phase shift -t " , and is then reflected on a totally reflecting mirror 102 and a second semitransparent plate 104 to a non-linear receiver Plate 10δ is deflected to a diffraction grating 36 , at which it experiences a frequency shift, and then arrives at the receiver 42, "Another semitransparent plate 108 splits off part of the partial wave 10 and feeds it to a second non-linear detector 54. A semitransparent plate 110 splits off part of the partial wave whose frequency is shifted by the diffraction grating J> 6 and also feeds this split off part to the detector 54 via a further semitransparent plate 112. The detector 54 therefore sends a signal of the form z '= d- cos (w ¹ - w) t to a circuit 26, while the receiver 42 sends the circuit 26 with a signal ζ of the form ζ = c cos [(w ¹ - w) t --f] feeds.

The advantage of the structure according to Fig. 6 is that that the detector 54 is not affected by a phase

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shift subject radiation can be taken, so that the required in the measuring arrangement according to Fig. 2, small incorrect settings for the embodiment according to FIG. 6 can be dispensed with. -

According to the above explanation of the optical properties of a ^w eöan- designed according to the invention. Order based on the representations in FIGS. 2 and 6 is now intended to be the actual measurement of the phase shift

<f will be explained on the basis of the electrical signals emitted by the receiver 42 or by the receiver.

For the extraction of the phase shift -P from the signal ζ, the phase of this signal ζ must be compared with the phase of the signal ζ ', which has the same frequency w ^J - w, but not the term going back to the phase shift f contains. In the illustration of FIG. 4, the two low-frequency signals ζ and z 'are superposed on each other. The upper half of FIG. 4 reproduces the signal ζ, which has the amplitude c and the angular frequency w'-w and contains a phase shift · ΐ , while in the lower half of FIG. 4 the signal z 'with the amplitude d and the angular frequency w'-w is shown. The signal ζ goes at a time t, through 0, which compared to the time t for. the zero crossing of the signal z 'is delayed by the difference t, -t- = rf / w'-w. By introducing the period T of the low-frequency signals, this relationship can also be written:

According to the invention, an electronic circuit can therefore be used for measuring the phase shift -f, for which two possible design variants are illustrated in FIG. _: , " ^:

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The first of these embodiment variants, which is shown in Fig. 5 in the upper half, contains a detector 70 for the detection of the time t, the zero crossings of the signal z supplied by the receiver 42, a detector 72 for the detection of the time t of Zero crossings of the signal z ¹ supplied by the detector 5 ^, a circuit 74 for measuring the difference between the times t, and t, a frequency meter for measuring the frequency w'-w of one of the two signals ζ or z ¹ , which is also called a chronometer can be designed for measuring the period T of the signals · or z ¹ , and a circuit 78 which outputs the phase shift -Ϋ at its output, for example in the form of the relative values' -F / 2t [. ...

The circuit shown enables permanent measurement of the phase shift i. Now, however, there are cases in which the milieu 16 with phase shift., N3 has a very short life, during which one. the speed of rotation for the diffraction grating can be regarded as known or even constant. The metal disk forming the diffraction grating generally has a considerable inertia and its speed of rotation remains practically constant for several seconds when it is driven by a DC motor fed by a stabilized current source When it comes into effect for a fraction of a second, it makes no sense to derive ^{the signal z 1} at any moment with the aid of the components shown in dash-dotted lines in FIGS the

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Λ then the phase (w'-w) t-- | of the signal ζ can be compared. This reference phase can then be obtained with the aid of the receiver 42 before the radiation passes through (Las Milieu 16 with phase shift ^ that is, before it has an effect on the phase position, by then assuming a known and, for example, constant value for the frequency w ^l -w is stored, this assumption being largely verified if the phenomenon leading to the phase shift is only brief The same receiver ^ 42 then serves to recognize the signal ζ.

In this advantageous embodiment variant, the electronic circuit can be constructed as shown in FIG are given the same reference numbers as there. A detector 70 fed with a low frequency signal provided by the receiver 42; determines the zero crossings of this signal before the occurrence of the phenomenon leading to the phase shift. The corresponding times are equivalent to the times t- for "the zero crossings of the signal ζ ^! which is not phase shifted. This information is stored in a memory 80 connected to the detector 70 The memory 80 is also connected to a frequency meter J6 , via which it is ^{fed with the frequency w f} - w or the period T, and on the basis of these two pieces of information the times t for the zero crossings of the phase (w'-w ) t. If the phenomenon leading to the phase shift occurs, the detector 70 still determines the times for the zero crossing of the signal emitted by the receiver 42,

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and these times are this time equivalent to the times t, for the zero crossings of the signal z. The times t determined in this way can then be compared with one another in a circuit 74 connected to the memory 80 on the one hand and the detector 70 on the other hand, at whose output a difference t _? -t corresponding signal appears.

In the two embodiment variants shown in FIG. 5 for the electronic circuit for measuring the phase shift J , the times for the zero crossings of the low-frequency signals are determined with the aid of electronic clock generators, which are known to the person skilled in the art. The accuracy for measuring the difference t, -t between times t. and t and thus the measurement of the phase shift is in principle only limited by the accuracy of the clock generator used. It can therefore be very large if the beats are at a low frequency. The measurement can be made in each period of the low-frequency signal or even twice in each period if the times for both zero crossings of the signals ζ and z ^{1 are} determined.

In this way, the applicant was able, for example, to achieve an accuracy better than 2 ^ fIO "for the measurement of the phase shift ^, with a measurement being made every 10 seconds, which corresponded to one measurement per period of the low-frequency signal, since the Doppler shift on w ¹ - w = 2 '<10 Hz was set.

In a preferred embodiment variant for the circuit for measuring the phase shift f , the detectors 70 and 72 and the frequency meter 76 and the

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associated circuits 74 and. 78 in digital Kind of executed.

In another, simpler variant, the two low-frequency signals ζ and z '"can be made visible on the fluorescent screen of a two-channel oscilloscope. The phase shift between the two signals is then estimated visually, which is sufficient for certain applications where the fluctuations in the phase shift ' ^ done slowly.

In yet another embodiment, the circuit for measuring the phase shift Jf can measure the differential phase shifts from one period to another, which is then followed by an integration of these differential phase shifts, as a result of which the total phase shift can be obtained.

In the same way, as a third embodiment variant also use a device with a modulation core defined above, whose mode of operation corresponds to the relevant person skilled in the art is familiar. "

The arrangement described above has numerous possible uses; .

a) The system with phase shift can for example be a plasma that is temporarily or permanently present is. The refractive index η of a plasma for radiation of frequency w is known to be:

40 9819/103 3

^-20-23531

where w denotes the plasma frequency, which in turn is given by the relationship:

w _p = (K Ne ² / *) "!. (2)

in which N denotes the electron density of the plasma.

The phase shift 4 ^; for a wave after two passes through a container of length L containing such a plasma then results in:

f = 2 (w / c> J (1-n) dl (3)

where η is calculated from the relationships given above. In this way, the measurement of the phase shift -P according to the invention enables an accurate and rapid determination of the electron density in a plasma.

b) The system with phase shift can continue

be a substance whose index of refraction is not known and for which the variations in this index of refraction are to be measured. The measured phase shift j ' is then related to the refractive index of interest via equation (3) given above.

c) The system with phase shift can still be any structural element whose movement (translation, Rotation or vibration) a displacement of the reflecting or scattering surface and thus causes a phase shift of the radiation reflected or backscattered on this surface. In this way

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the fluctuations in the radius of a to determine the rotating body rotating around its own axis, by directing the measuring radiation onto the outside of this rotating body. The variations in the Radius de? Rotary bodies then lead to fluctuations in the phase shift of the incident light waves, which can be detected with the aid of the measuring arrangement designed according to the invention, whereby the possibility a precise production control for rotating body results. One is of particular advantage Application to the measurement of the diameter of turbines. This measuring method has the advantage that none material contact with the moving rotating body is required for the measurement.

d) Permitted in the field of meteorology measuring arrangement designed according to the invention of displacement measurements .;

The possibility of using a hydrogen cyanide acid laser (HCN laser) with an output radiation of wavelength 357 M as a radiation source has already been mentioned as an example. It goes without saying that other radiation sources can also be used, for example COg lasers which emit an output radiation with a wavelength of 10.6 / rev. In general, the field of infrared radiation is of interest, this radiation proving to be particularly advantageous for measuring high plastic densities. For plasma densities in the order of magnitude

! "5 14 -3 '■ ■ ■
from 10 to 10 cm, as it occurs in devices for the investigation of a thermal core dislocation,

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namely, the plasnia frequency w, as defined by equation (2) given above, is approximately in the case of microwaves in the millimeter range, which are therefore poorly matched. On the other hand, if you can

2 2

Chooses w large because of w, the refractive index η des

P 2/2

Plasmas to η approximately equal to 1-w / 2w, and the phase shift -f results in: -

L ρ
3) ' W dl

Since this phase shift is then inversely proportional to the frequency w of the probing wave, there is none Interested in using radiation of too high a frequency, such as radiation in the ' Visible light range. The 'infrared part of the spectrum therefore forms a privileged zone where the Measurement of high plasma densities is possible while the microwaves are being cut by the plasma, and the density measurement is carried out with high sensitivity.

The measuring arrangement designed according to the invention shows an excellent efficiency, whereby how already mentioned above, the relatively low emission power of the HCN laser known today is not an obstacle their use represents more, as is the case with the previously known measuring arrangements. Also can Very simply built pyroelectric detectors can be used that operate at near room temperature lying temperature work; for example, detectors made of glygocole sulfate, so-called T.G.S., come in Consideration. The bandwidth of these detectors - today in the order of 100 kHz - sets the upper limit for

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the usable Doppler shift. It should be added that the measurement, according to the phase shift of the invention is independent of the amplitude of the e falling waves or partial wavesida them alone the determination of the times for the zero crossings of the different phases. In this way the measurement becomes independent of the inevitable fluctuations in the intensity of the radiation emitted by the radiation sources and in particular the lasers.

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Claims (4)

Claims 1 / Measuring arrangement for measuring the phase shift V triggered by a system for phase shifting in electromagnetic radiation, characterized in that it. a source (2) for electromagnetic radiation (4) which emits a wave of the form χ = a cos wt, a beam splitter (6; 30; 100) fed with this wave, which divides the wave supplied to it into two partial waves (8,10 ] 32, 34) splits a rotating cylindrical diffraction grating (36) to which one of these partial waves is fed "and which ^{shifts the frequency of this partial wave by an amount w f} - w = (v / c) w, where c for the The speed of light and ν stand for the component of the linear grating speed along the direction of the wave at its point of impact, a system (l6) for phase shifting arranged on the path of one of the two partial waves, which shifts the phase of the wave fed to it by the value -P , a combining element (20) for re-combining the two partial waves shifted in frequency and phase with respect to one another, a first non-linear detector (42) fed with the beam emitted by this combining element, which has a low frequency tes electrical signal z = c cos ["(w ¹ -w) t- -f 3 emits and has a device (26) connected to the output of this detector for measuring the phase shift Ϋ contained in this low-frequency electrical signal. 2. Measuring arrangement according to claim 1, characterized in that that the diffraction grating (36) is an Eehelett £ grating working in autocollimation. 409819/1033 3. Measuring arrangement according to claim 2, characterized in that that the diffraction grating (36) is a metal disk rotating about its axis, into which along its eye ends Steps are incised. ■ ' ■ - 4. Measuring arrangement according to one of claims 1 to 3, characterized characterized in that the radiation source (2) emitted radiation is in the range of the infrared Has wavelength. 5. Measuring arrangement according to claim 4, characterized in that that the radiation source (2) is a laser. ■ 6. Measuring arrangement according to claim 5 *, characterized in that that the laser is a hydrocyanic acid laser (HCN laser) is that-a radiation with a wavelength of Releases 337 microns. '' ·. Measuring arrangement according to Claim 5, characterized in that the laser is a CO ₂ laser, the one. Emits radiation with a wavelength νοηΙΟ, ό microns. ^: -. Measuring arrangement according to one of Claims 1 to .7, characterized in that the beam splitter (6) and the combining element (20) form a Mach-Zehnder interferometer. 9. Measuring arrangement according to claim 3 *, characterized in that that they also have a first semitransparent plate (108) which forms part of the one partial shaft (10). before their frequency shift through the serving diffraction grating (36) accommodates a second semi-transparent plate (110) which part of the partial wave (10) after its frequency shift diarch the rotating diffraction grating (36) accommodates a third semi-transparent plate (112) which 409819/1033 the two parts of the picked-up wave are combined, a second non-linear detector (5 ¹ O, which receives the combined beam emitted by the third semitransparent plate and ^{emits a low-frequency signal z 1} = d cos (w'-w) t, and in its Device (26) for _% measuring the phase shift ■ a first circuit (72) fed with the low-frequency signal z ', which determines the time t of the zero crossings of this signal z ¹ , a second circuit (70) fed with the low-frequency signal ζ " ), which determines the time t, the zero crossings of this signal ζ, and a measuring circuit (74) for measuring the phase shift -P resulting distance t.-t between the times t 1 and t. 10. Measuring arrangement according to claim l for measuring temporary phase shifts -P with a known value of the frequency shift w'-w, characterized in that the device (26) for Hessen the phase shift f has a detector (70) for determining the times t or .t .. of the zero crossings of the signal emitted by the first non-linear detector (42) before or after the action of the system (16) for phase shifting the waves (8 or 10) supplied to it, one with the detector (70 ) connected memory (80) for storing the measurement results obtained before the action of the system (16) with phase shift on the wave η for the times t and one to the output of the detector (70) and one to the output of the memory (80) ) Connected measuring circuit to determine the difference t.-t between the time 1 ο points t, and t and thus, the phase shift of interest f contains. 409819/1033 11. Measuring arrangement according to claim 9 or 10, characterized in that the device (26) for measuring 'the phase shift ψ carries out a measurement for each period T of the low-frequency signal. ; ¹ JIiXX. -. "." I. "12. Measuring arrangement according to one of claims 1 to 11, characterized in that the system (16) with phase shift consists of a plasma, the electron density of which can be measured by way of the phase shift ^ f. ■ 1J> · Measuring arrangement according to one of Claims 1 to 11, characterized in that the system (16 ·) has a phase shift from the one upwelling partial wave. ' _t reflective and / or scattering surface of a moving component. 14. A measuring arrangement according to claim \ J>, characterized in that the component rotates about its own axis and absorbs the incident wave on its outer surface, the phase shift ^ varying in the same way as the radius of the rotating component. 15. Measuring arrangement according to Claimu ^. » characterized in that the component is subject to an oscillatory movement, the amplitude of which can be measured in the form of the phase shift "f . '■'. ■ ■ / ■■■■■ '" ■. . - 16. Measuring arrangement according to one of claims 1 to 11, characterized in that the system (16) for phase shift is a material with unknown optical expansion cortex jx η, the variation of which is the variation of the Phase shift corresponds to y. 409819/1 033 17. Measuring arrangement according to one of claims 1 to 9, characterized characterized in that the non-linear detectors (42 and 54) are of the pyroelectric type. 409819/1033