WO1992006353A1 - Interferometre - Google Patents

Interferometre Download PDF

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Publication number
WO1992006353A1
WO1992006353A1 PCT/AT1991/000106 AT9100106W WO9206353A1 WO 1992006353 A1 WO1992006353 A1 WO 1992006353A1 AT 9100106 W AT9100106 W AT 9100106W WO 9206353 A1 WO9206353 A1 WO 9206353A1
Authority
WO
WIPO (PCT)
Prior art keywords
measuring
waveguide
interferometer according
beam splitter
interferometer
Prior art date
Application number
PCT/AT1991/000106
Other languages
German (de)
English (en)
Inventor
Gerhard Leuchs
Original Assignee
Tabarelli, Werner
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Tabarelli, Werner filed Critical Tabarelli, Werner
Publication of WO1992006353A1 publication Critical patent/WO1992006353A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02049—Interferometers characterised by particular mechanical design details
    • G01B9/02051—Integrated design, e.g. on-chip or monolithic
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02056—Passive reduction of errors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02075—Reduction or prevention of errors; Testing; Calibration of particular errors
    • G01B9/02078—Caused by ambiguity
    • G01B9/02079—Quadrature detection, i.e. detecting relatively phase-shifted signals
    • G01B9/02081—Quadrature detection, i.e. detecting relatively phase-shifted signals simultaneous quadrature detection, e.g. by spatial phase shifting

Definitions

  • the invention relates to an interferometer, in particular for determining the distance or displacement path of a movable component, with a laser light source, with an asymmetrical beam splitter for the intensity-uneven division of the light emitted by the laser light source into a reference beam and one Measuring beam, which is guided over a measuring path running at least partially in a gaseous ambient medium and leading over a movable measuring mirror, with a recombination device on which the reference beam guided over a reference path and the measuring beam returning from the measuring mirror interfere, and with a detector device for analyzing at least one optical interference signal emerging from the recombination device.
  • interferometers are suitable for determining the distance or determining the displacement path and thus for detecting the position or changes in position of movable components, for example machine components.
  • a practically unavoidable wavefront distortion of the measuring beam coming back from the measurement section is a problem.
  • Such wavefront distortions result from air streaks and, above all, from contaminations (oil vapors, etc.) of the air occurring in industrial use in which the measurement is located ⁇ beam propagates, as well as from inaccuracies of the optical components used.
  • the latter inaccuracies of the optical components could at best be avoided by correspondingly expensive components.
  • the wavefront distortions mentioned lead to a change in the observed spatial interference pattern and thus to a falsification of the measurement result.
  • the known wavefront distortions also have an unfavorable effect in known two-frequency heterodyne interferometers, in which the beat frequency between the measuring and reference beams is observed at a slightly different frequency. This is because, like already slight deviations from the ideally exact adjustment, they reduce the quality of the interference, that is to say the modulation deviation of the oscillating interference signal to be evaluated in relation to the signal background. This leads to problems.
  • the signal from the photodetector must be electrically amplified for the evaluation.
  • measurements should also be carried out very quickly, so that the mirror speed can be up to a few meters per second.
  • the generally difficult task is to amplify a small signal which is seated on a large background. This is particularly a problem if the surface is not completely stable over time and therefore cannot be easily subtracted electronically.
  • Detection systems which have the required amplification at high bandwidth are highly sensitive, low-capacity detectors, e.g. B.
  • avalanche diodes combined with very low-noise electronic amplifier circuits, or secondary electron multipliers (photomultiplier), which the photo- Combine electrical detection and electrical amplification in a high-voltage vacuum tube.
  • secondary electron multipliers photomultiplier
  • the object of the invention is to provide a compact interferometer with which measurements can be carried out quickly even under harsh environmental conditions and which is therefore particularly suitable for industrial use.
  • This is achieved according to the invention in that a spatial filter device is arranged between the measuring mirror and the recombination device, through which the measuring beam returning from the measuring mirror is guided.
  • the ratio of the desired signal component to the background in the photoelectric interference signal is still at a maximum when the loss of measuring beam power generated in the spatial filter is zero. So the spatial filter alone cannot solve the problem of a too large background or amplifier saturation. Only the combination according to the invention of asymmetrical beam splitter and a spatial filter device in the measuring beam allows the elimination of the signal background and thus a highly amplifiable output signal for the use of highly sensitive, fast detection and amplifier systems.
  • the photoelectric signal is then: I - ⁇ ⁇ ' R « ac ⁇ ⁇ i £ t) ⁇ ⁇ ⁇ - ⁇ (lR) -a» cos ⁇ j £, t * kL >> a > time average - R * a a / 2 * ⁇ - (lR) .a a / 2 + «f ⁇ - « (1-R> .a a -cos ⁇ kL), where w is the angular frequency, k is the wave number and L is the optical path difference between the reference and Are measuring beam.
  • the angle brackets " ⁇ > time average" indicate that averaging takes place over a light period, so that the zero oscillating threshing floor quickly falls out.
  • the absolute size of the interference signal is reduced, but the constant background can be brought to zero by a suitable choice of the division ratio on the beam splitter.
  • the condition for R is:
  • the spatial filter device is arranged at the end of the part of the measuring section running in the gaseous ambient medium. This completely eliminates the wavefront distortions that occur mainly on the free measuring section running in the surrounding medium. Between the spatial filter and the recombination device there is hardly any risk of renewed wavefront distortions of the "cleaned" measuring beam. If the spatial filter is formed by a coupling-in lens and the entry end of a single-mode waveguide, the measuring beam, which is justified in the wavefront, can be guided without further interference with a well-defined wavefront to the recombination device and there can interfere perfectly with the reference beam .
  • a beam splitter with a symmetrical division ratio of 1: 1 can advantageously be used as the recombination device.
  • the asymmetrical beam splitter for division into measuring and reference beams and the recombining device are separate elements, which may, however, be formed on one and the same carrier substrate (wafer).
  • the division ratio of the asymmetrical beam splitter is preferably adjustable in order to allow a perfect adaptation to the respective circumstances.
  • the measuring beam at the measuring mirror is not thrown back into itself, but is coupled into a second single-mode waveguide with a beam offset by means of a separate coupling lens (or a coupling lens arrangement combined from several to form a lens system).
  • a separate coupling lens or a coupling lens arrangement combined from several to form a lens system.
  • the beam offset change occurring when the retroreflector is laterally shifted can be easily mastered with a suitable choice of the coupling and decoupling lenses, that is to say that the meeting of the second single-mode waveguide or coupling lens is relatively uncritical when the waveguide returns from the measuring path - is table.
  • the retroreflector has preferred have a triple mirror or triple prism, the property of the tilt invariance (even when the retroreflector is turned, the reflected beam remains parallel to the incident beam), which has an advantage over longer mirrors compared to flat mirrors.
  • a triple mirror reflects incident light rays parallel to itself in a specific solid angle range.
  • the adjustment effort in the area of the measuring beam is considerably reduced.
  • the interferometer is then correctly adjusted (assuming a relatively simple pre-adjustment of the other optical components) if sufficient light is coupled into the second glass fiber.
  • this is not particularly critical due to the property of the retroreflector to always reflect rays back in parallel, and due to suitable lens dimensions.
  • the interferometer will advantageously be designed such that the single-mode waveguide from which the measuring beam is coupled out and the second single-mode waveguide lie parallel in their end region facing the measuring section.
  • the separate coupling-in and coupling-out lens and waveguide it can preferably be provided that at least the end regions of the single-mode waveguide facing the measuring section, from which the measuring beam is coupled out, and of the second single-mode waveguide a common carrier are fixed, the coupling and decoupling lenses being attached to this carrier. If a flat measuring mirror is nevertheless to be used, an optical attachment can ensure that the returning beam enters the second waveguide is coupled. If it is a single-mode waveguide, the wavefront in the waveguide is almost ideal. Wavefront distortions along the measurement path only worsen the coupling into the waveguide.
  • Such a waveguide can expediently be designed as a waveguide path which is diffused onto a wafer.
  • the single-mode waveguide of the interferometer, the beam controller and the recombination device are integrated on the same wafer, and the reference beam and the interference signal originating from the recombination device are also guided in single-mode waveguide paths. which are diffused into the same wafer.
  • This integrated design means that most of the optical components are pre-adjusted and you get ideal interference between the reference beam and the measurement beam "cleaned" of wavefront distortions. Due to the almost exclusive use of integrated optical components, a considerable price advantage can be achieved compared to known interferometers.
  • the use of waveguide tracks diffused into a wafer for an interferometer is indeed known per se. In the known integrated interferometer, however, the measurement beam emerging from the waveguide path is partially thrown back into the same waveguide by a plane mirror arranged at a small distance from the exit point, which leads to undesired feedback into the light source.
  • the beam splitter and the recombination device may be separate optical elements.
  • the light originating from the light source is present in the entire interferometer arrangement except for the measuring section running through the retroreflector in the surrounding medium between the coupling and decoupling lens (and optionally) is guided into the area behind the recombination device in single-mode waveguides, the beam splitter and the recombination device being formed by waveguide couplers.
  • Figures 1 to 3 show schematic representations of exemplary embodiments of the interferometer arrangement according to the invention.
  • the interferometer arrangement shown in FIG. 1 has a laser light source 1 (preferably a laser diode), the light of which is coupled into a single-mode waveguide track 2, which is diffused onto a wafer 3 made of lithium niobate.
  • a beam splitter B with an asymmetrical division ratio in favor of a higher measuring beam line the division into the measuring beam takes place, which is initially continued in the waveguide path 4 and into the reference beam, which is also integrated in the reference branch 5 in the wafer 3 via a mirror 6 to the recombina ⁇ tion device A leads.
  • the measuring beam emerges from the waveguide 4 and is collimated with a decoupling lens 7.
  • the measuring section now leads through the gaseous ambient medium (usually air) and via a retroreflector 8 (triple mirror), which, for example is attached to a tool slide (not shown).
  • This retroreflector 8 sends the measurement beam back parallel offset, with a lateral displacement of the retroreflector or its tilting the direction of the retroreflective
  • Measurement beam does not change, but only its parallel offset to an uncritical extent.
  • the measuring beam returning from the retroreflector 8 is coupled into a second single-mode waveguide 11 by a separate coupling lens 9. This prevents feedback of disruptive laser light into the laser diode 1.
  • the spatial filter device is essentially formed by the lens 9 arranged at the end of the free measuring section and the single-mode waveguide 11, that is to say in the exemplary embodiment shown in FIG. 1 the surface 10 arranged in the focal plane of the lens 9 acts around the focal point in FIG Wafer 3 diffused single-mode waveguide 9 as a spatial filter, which fades out intensities caused by wavefront distortions lying outside the focal point region. Since it is a single-mode waveguide, the wavefront of the measurement beam coupled into the waveguide 11 via the lens 9 is almost ideal and can therefore interfere perfectly with the reference beam. Wavefront distortions along the measurement path via the retroreflector 8 only lead to a deterioration in the coupling.
  • the measuring beam returning from the measuring section is brought into interference in the recombination device designed as beam splitter A with a symmetrical division ratio with the reference beam guided in the reference branch 5.
  • the interference signals are then detected by detectors 12a-d and evaluated in an electronic evaluation circuit, not shown.
  • the division ratio R of the asymmetrical beam splitter B is now selected so that the power losses (1- ⁇ ) on the measurement section and in the spatial filter 9, 10, 11 are compensated by correspondingly more light (1-R) on the measurement section is sent.
  • Typical values of R are between 10% and 30%.
  • R ⁇ / (l + ⁇ ) the constant signal background can be reduced to zero and highly sensitive photoelectric detectors suitable for the detection of fewer photons can be used.
  • the typical light output on one of the detectors is approximately 2 ⁇ W.
  • the measuring time interval is 10-50 ns. During this time, only 60,000 to 300,000 photons arrive at the detector.
  • the detectors 12a-d are only shown schematically and can be, for example, secondary electron multipliers or avalanche diodes with an electronic amplifier circuit.
  • the exemplary embodiment shown is a single-frequency interferometer, in which two different polarization directions of the light emitted by the light source 1 are used in order to obtain information about the direction of movement of the retroreflector 8.
  • a polarization-dependent phase retarder 13 is integrated in front of the recombination device, which causes, for example, a relative phase difference of 90 * between the two directions of polarization.
  • the two complementary outputs of the recombination device A are connected by way of waveguide tracks 14 and 15 diffused into the wafer 3 with polarizing beams 16 and 17, the outputs of which lead to the photo detectors 12a-d mentioned.
  • these photodetectors 12a-d receive interference signals which are shifted relative to one another, from which not only the displacement path of the retroreflector 8 but also its displacement direction can be clearly determined. Furthermore, from the detection of the intensities of both complementary outputs 14 and 15 of the recombination device A, influencing factors (thermal drifts of the mechanics and electronics, fluctuations in intensity of the light source, fluctuations in intensity due to slight misadjustments), which otherwise lead to measurement errors in homodyne operation can eliminate, so that it can be determined whether changes in intensity only due to the change of influencing factors or actually from a movement of the retroreflector. After combining the measurement and reference beam, one not only uses an interference signal beam, but also uses the second output of the beam splitter, which delivers a complementary interference signal. Now everyone
  • the coupling of the measurement beam into a second single-mode waveguide and the associated spatial filter effect and the ideal wave fronts in the single-electrode waveguides ensure that complementary interference signals are actually well-defined even under industrial conditions which can then be reliably evaluated by the electronics.
  • the interferometer arrangement according to the invention can also be operated heterodyne, two light frequencies having slightly different frequencies being used.
  • the lithium niobate material used has the advantage that acousto-optical modulators can also be integrated, these being vaporized in order to obtain a light frequency shifted by the acoustic frequency.
  • Such an acousto-optic modulator would then have to be installed shortly before the measuring beam emerges from the wafer 3. it would be recommendable to install a second acousto-optic modulator with a modulation frequency different from the first modulator in the reference beam in order to avoid direct crosstalk into the detection electronics.
  • only one detector is then required instead of the four photo elements 12a-d.
  • the polarization-dependent phase retarder and the polarization beam splitters 16 and 17 can also be omitted.
  • the integrated design in which the light in the wafer is guided in single-mode waveguide tracks, achieves a compact design and excellent interference between the reference beam and measuring beam, since both have ideal wavefronts in the single-mode waveguides.
  • a large part of the optical components can already be pre-adjusted.
  • the interferometer is also largely independent of the temperature of the wafer 3.
  • Particularly suitable as light sources Laser diodes 1 because they take up little space and are inexpensive.
  • the measurement result of an interferometer is available in units of the air wavelength present on the measurement section, which in turn depends on the frequency of the light and the refractive index of the surrounding medium (mostly air), it is advantageous to continuously determine this air wavelength using your own device.
  • the frequency of the light source is known, a refractive index determination is sufficient to know the air wavelength.
  • the refractive index can be determined the so-called parameter method can be determined by determining the air temperature, the air humidity and the air pressure. If you want to determine the wavelength of light in the air directly, you can compare it with a measuring standard (etalon) in which the same environmental conditions prevail as on the measuring section. In such a case, it is necessary to divert light originating from the light source from the actual interferometer. In the simplest case, this is done using a beam controller C, which is arranged immediately after the light source in the beam path.
  • the measure of leading the measurement beam in front of the measurement section in the surrounding medium in a single-mode waveguide and then guiding it via a decoupling lens to the measurement section achieves excellent constancy and reproducibility of the optical beam guidance.
  • glass and gallium arsenide are also suitable as wafer materials.
  • optical fibers in particular glass fibers
  • the interferometer shown in FIG. 2 is used to record the displacement of a movable component (not shown) on which the triple mirror 8 is favorably attached directly.
  • the light originating from a laser is coupled into the glass fiber 2 and then reaches the coupler B, which has an asymmetrical see division of the light into the glass fiber 4 belonging to the measuring branch and the glass fiber 5 belonging to the reference branch.
  • the light from the glass fiber 4 reaches the measurement section actually running in the ambient medium (air) and is reflected back parallel to itself with a beam offset by the triple mirror 8.
  • a special coupling-in lens 9 couples the back-reflected measuring beam into a second single-mode waveguide (glass fiber 11), the spatial filter effect again being used and wavefront distortions being "straightened".
  • the end regions of the glass fibers 4 and 11 facing the measuring section are advantageously parallel, which means that there is always a good coupling of the measuring beam returning from the measuring section into the glass fiber without complex deflection devices when the triple mirror 8 is displaced 11 is given.
  • these can be fastened on a common carrier 18, which advantageously also carries the decoupling lens 7 and the coupling lens 9, which also means their relative Adjustment to the glass fibers 4 and 11 is ensured.
  • the coupling lens 9 and the coupling lens 7 are advantageously of the same design and in particular have the same focal length.
  • Gradient index lenses which can be attached directly to the carrier 18 via their flat connection surface, are particularly suitable as the coupling-in and coupling-out lenses.
  • the light returned from the measuring section in the glass fiber 11 and the light guided in the glass fiber 5 of the reference branch are recombined in the symmetrical coupler A.
  • the preferably 90 ° phase shift between the two polarizations for detecting the direction of movement of the measuring carriage can be achieved in a known manner via total reflection in the triple prism or with a birefringent quarter wave plate (not shown in FIG. 2) in the measuring beam.
  • the interference signals at the two outputs from coupler A are detected separately with a polarization beam splitter or with a beam splitter and polarizer according to the polarization states which are perpendicular to one another (schematically illustrated detectors 12a, b, c, d).
  • the polarization-state-dependent division is carried out over two beam splitters AI * and A2 'and four polarization filters 26a-d arranged in front of each detector 12a-d. If polarization beam splitters are used instead of the beam splitters AI 1 and A2 ', the polarization filters 26a-d can be omitted.
  • the polarization-dependent signal division can alternatively also take place as shown in FIGS. 2a and 2b (in the variants of these figures, the arrangement in front of the recombination device A is the same as in FIG. 2).
  • a lens 27 is provided, which is arranged just before the two exit points of the recombination device A.
  • the two beams imaged by the lens 27 reach a polarization beam splitter A3 and from there to the four detectors 12a-d.
  • FIG. 2b compared to the variant shown in FIG.
  • the beam splitter is used AI * and A2 'are dispensed with and the divergent radiation cones 28, 29 from the two exit fibers of the recombining device A are used in order to achieve a spatial and ultimately the polarization state-dependent signal distribution via the polarization filters 26a-d.
  • the detectors 12a-d are connected to an electronic evaluation circuit 19 which, for example, calculates and displays the position of the measuring mirror 8.
  • the light originating from the light source 1 is guided in single-mode waveguides (glass fibers) up to the measuring section running in the ambient medium, which largely eliminates the influence of stray light and during recombination in the coupler A there are well-defined wavefronts in the measuring branch glass fiber 11 and in the reference branch glass fiber 5, which guarantee an excellent interference signal.
  • the spatial filter effect which occurs when the measuring beam returning from the measuring section is coupled into the glass fiber 11 eliminates any wavefront distortions that may be present.
  • the higher losses on the measurement section and in the spatial filter 9, 11 can be compensated for by the asymmetrical beam splitter B.
  • the beam expensive for dividing the light in the measuring beam and reference beam is also used as a recombination device at which the measuring beam and the reference beam are brought into interference.
  • the beam splitter (coupler B) and the recombination device (coupler A) have separate op- Table components are to reliably exclude the effects of laser light on the light source.
  • the sum of the glass paths in the glass fibers 4 and 11 and the path in the glass fiber 5 are preferably of the same length in order not to have any relative changes in length between the reference and measuring branches in the event of temperature fluctuations.
  • the spatial filter device 30 can also be implemented by a lens-pinhole-lens combination, as shown in FIG. 3. Such a combination could also be retrofitted with existing interferometers with discrete optical components.
  • the measurement beam 31 returning from the measurement section is focused by a converging lens 32 onto the opening of the perforated diaphragm 33 and then collimated by a collimation lens 34.
  • the pinhole 33 dazzles higher spatial frequencies originating from wavefront distortions zen out, since these are located radially outside in the focal point region of the lens 32, where the opening of the pinhole 33 is arranged.
  • the interference signal 36 which contains no signal background due to a suitable choice of the division ratio of the asymmetrical beam splitter (not shown) for division into the measurement and reference beam, passes through a lens 37 to a highly sensitive amplifier 38.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)

Abstract

Un interféromètre de mesure de la distance ou du trajet de déplacement d'un composant mobile comprend une source (1) de lumière laser et un diviseur de faisceau (B) ayant un rapport asymétrique de division qui subdivise la lumière émise par la source de lumière laser en un faisceau de référence et en un faisceau de mesure. Le faisceau de mesure est guidé dans une section de mesure qui s'étend en partie dans l'air et à travers un miroir mobile de mesure (8). Dans un dispositif recombinant (A), le faisceau de référence guidé dans une section de référence (5) interfère avec le faisceau de mesure de retour de la section de mesure. Un dispositif détecteur (12a-d, 19) de haute sensibilité analyse les signaux d'interférence qui sortent du dispositif recombinant (A). Le faisceau de mesure de retour de la section de mesure est guidé à travers un filtre tridimensionnel (9, 10, 11; 30) afin d'éliminer des distorsions du front d'onde. Par un choix approprié du rapport de division du diviseur de faisceau (B), on peut éliminer le bruit de fond du signal d'interférence.
PCT/AT1991/000106 1990-10-01 1991-10-01 Interferometre WO1992006353A1 (fr)

Applications Claiming Priority (2)

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AT197390 1990-10-01
ATA1973/90 1990-10-01

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WO1992006353A1 true WO1992006353A1 (fr) 1992-04-16

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0646767A2 (fr) * 1993-10-05 1995-04-05 Renishaw plc Dispositif de mesure de distance par interférométrie
US20230266116A1 (en) * 2022-02-23 2023-08-24 Lockheed Martin Corporation Optical systems with controlled mirror arrangements

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0286528A1 (fr) * 1987-04-07 1988-10-12 Commissariat A L'energie Atomique Capteur de déplacement en optique intégrée
DE3837593A1 (de) * 1988-11-05 1990-05-10 Kerner Anna Wellenlaengenstabilisierung
US4941744A (en) * 1987-07-07 1990-07-17 Tokyo Kogaku Kikai Kabushiki Kaisha Integrated-photocircuit interferometer

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0286528A1 (fr) * 1987-04-07 1988-10-12 Commissariat A L'energie Atomique Capteur de déplacement en optique intégrée
US4941744A (en) * 1987-07-07 1990-07-17 Tokyo Kogaku Kikai Kabushiki Kaisha Integrated-photocircuit interferometer
DE3837593A1 (de) * 1988-11-05 1990-05-10 Kerner Anna Wellenlaengenstabilisierung

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0646767A2 (fr) * 1993-10-05 1995-04-05 Renishaw plc Dispositif de mesure de distance par interférométrie
EP0646767A3 (fr) * 1993-10-05 1996-01-03 Renishaw Plc Dispositif de mesure de distance par interférométrie.
US5541730A (en) * 1993-10-05 1996-07-30 Renishaw Plc Interferometric measuring apparatus for making absolute measurements of distance or refractive index
US20230266116A1 (en) * 2022-02-23 2023-08-24 Lockheed Martin Corporation Optical systems with controlled mirror arrangements
US11841223B2 (en) * 2022-02-23 2023-12-12 Lockheed Martin Corporation Optical systems with controlled mirror arrangements

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