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WO1989006781A1 - Procede et appareil servant a effectuer des mesures d'une distance optique - Google Patents

Procede et appareil servant a effectuer des mesures d'une distance optique Download PDF

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Publication number
WO1989006781A1
WO1989006781A1 PCT/SE1989/000009 SE8900009W WO8906781A1 WO 1989006781 A1 WO1989006781 A1 WO 1989006781A1 SE 8900009 W SE8900009 W SE 8900009W WO 8906781 A1 WO8906781 A1 WO 8906781A1
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Prior art keywords
wave number
measuring
detector
change
time
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English (en)
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Hans Martin
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Geotronics AB
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Geotronics AB
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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
    • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
    • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
    • G01B9/02004—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using frequency scans
    • 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
    • G01B9/0207—Error reduction by correction of the measurement signal based on independently determined error sources, e.g. using a reference interferometer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/60—Reference interferometer, i.e. additional interferometer not interacting with object

Definitions

  • the present invention relates to a method for measuring an optical distance in accordance with the preamble of Claim 1, and also to apparatus for carrying out the metho
  • Such methods and apparatus are used normally for measuring distances, but can also be used for other purposes.
  • the interferometric methods can only be used for measuring distances which are shorter than approximately half the coherent length of the laser, i.e. in practice distances of less than about 50 meters. Since these methods are based on the known Michelson interferometer principle, it is necessary to transport a retroreflector on a slide or corresponding carrier, along the whole length of the measured path. During transportation of the retroreflector, one interference fringe is calculated for each half-wave ⁇ length of movement. The accumulated number of interference fringes will then give the total distance travelled, when the wavelength of the light beam is known.
  • a variant of this method utilizes two fixed wavelengths, a so-called two wavelength interferometer, where the differ ⁇ ence frequency, phase dependency of the distance in rela- tion to the transmitter, gives the distance.
  • the method can be generalized to the use of more fixed wavelengths than two.
  • US 4 729 653 also describes a reference interferometer which is used to provide a measurement unit for carrying out a fringecount in the measuring interferometer.
  • the reference interferometer is. constructed analog ⁇ ously with the main interferometer.
  • This construction is an unfortunate one. since it means that the reference interferometer will have large dimensions, e.g. a length of about one meter, whereby it is impossible to avoid dimensional changes, unless taking expensive and far reaching rectifying measures. Because of its particular construction, or configuration, this known reference interferometer is prone to take up vibrations from the surroundings, which can be highly deleterious from the aspect of fringe pattern formation. Furthermore, in this case no reference is made as to how the measuring result will be influenced by possible movement of the object whose distance is to be measured, or of the corrective measures which need to be taken should the object be moved.
  • One object of the invention is to maintain control of wave number so as to obtain accurate measurements in an optimum fashion.
  • Another object of the invention is to provide a method which will allow the effects of distances to and movements of the measurement object to be separated so as to enable both to be determined.
  • a further object of the invention is to provide a refer ⁇ ence interferometer which has small dimensions and which is therefore less sensitive or vulnerable to vibration.
  • Still a further object of the invention is to obtain a distinct output signal from the reference interferometer detector. Since the reference interferometer has small dimensions, the time distance between each fringe count will be relatively long, and definitely much longer than the time distance from the measuring interferometer. The more distinct the indication of the fringes from the reference interferometer the better.
  • the ability to select a wave number interval affords the advantage of enabling the inverval to be predetermined with extreme accuracy, for instance with the aid of atomic references.
  • FIG. 1 illustrates highly schematically an interfero ⁇ meter arrangement which utilizes a single mode laser and which is complemented in accordance with the inventive proposals;
  • Figure 2 is a diagram which is intended for use when determining occurrent discrepancies; and
  • Figure 3 is a block schematic illustrative of one em ⁇ bodiment of an electric circuit for the interferometer arrangement shown in Figure 1.
  • Figure 1 illustrates an exemplifying embodiment of an interferometer-type distance measuring apparatus, generally referenced 1 in the Figure, comprising a beam source 2, which should have the form of a single mode laser, a semiconductor laser or a diode laser, and which transmits continuously a coherent light beam 3, which is split into two beam parts by a beam splitter 4.
  • a beam source 2 which should have the form of a single mode laser, a semiconductor laser or a diode laser, and which transmits continuously a coherent light beam 3, which is split into two beam parts by a beam splitter 4.
  • One of these beam parts passes through a focusing system 5 to a measuring point 6, from where the beam is reflected back through the focusing system and through a further beam splitter 7 and onto a detector 10.
  • the other beam part is passed onto a stationary reflector 8 which directs said beam onto the further beam splitter 7, which in turn reflects the beam onto the detector 10.
  • the beam 13 located between the beam splitter 7 and the detector 10 will then include interfering light rays obtained from the two beam paths.
  • the interfering light- beam 13 exiting from the beam splitter 7 is detected homodynamically in a progressive manner as the wavelength of the coherent light changes.
  • the detector 10 is preferably placed in the centre of the interference pattern and is small enough to discern a fringe separately.
  • the detector 10 is connected to a counter 11.
  • the transmitting beam source 2 is also con ⁇ nected to a control circuit 12, which enables the given wave number of the light beam to be changed during the time period taken to determine a discrepancy between the optical wave paths of the aforesaid two beam paths.
  • the aforedescribed arrangement is thus based on inter ⁇ ference between a beam which is reflected from the point whose distance is to be measured, a so-called object beam, and a reference beam, which beams are brought together and then directed onto the detector 10. Assume that these two beams each illuminate the detector at intensities "I ..” and I ", respectively. When obj ref these beams illuminate the detector simultaneously, because of interference the intensity will be
  • the two beams are spaced coherently across the surface of the detector, i.e. the detector has an.area which includes at most one fringe and lies in the centre of the interference pattern.
  • I ⁇ l is then the value of the degree of coherence of the two beams for the time delay which applies when the path difference therebetween is "x".
  • k 1/X is the wave number for the light source of wave length " " .
  • This principle beam path is the same as that in a tradi ⁇ tional Michelson interferometer array, although measuring procedures differ essentially, since it is not necessary to move a mirror or like retroreflector from one position to another, when determining measurements.
  • the fundamental principle in fact requires no movable parts to be present.
  • N Ika-kb,
  • ⁇ d l/(2n lk_-l- b l).
  • This problem is best solved with a single mode semi ⁇ conductor laser. Such a laser is able to sweep over the wave number range concerned in some tens of nanoseconds (or at a slower speed if desired).
  • GaAlAs-diode lasers are excellent in this context and are also the cheapest lasers capable of being procured.
  • the desired wave number sweep can be achieved by rapidly changing the driving current of the semiconductor laser, which results in an adiabatic change in the optical length of the laser cavity, and therewith a continuous wave number scan.
  • the desired result can be achieved with change in the laser 100 mA drive current of only about 20 A.
  • a reference cell is used to measure the change in wave number required to effect a distance calculation in accordance with equation 2.
  • the beam transmitter 2 shall also be capable of transmitting a light beam with wave number change for the purpose of formulating a wave number interval located within pre-determined limits, wherewith the aforesaid discrepancy can be determined from the dependency of the phase change on the change in wave number.
  • the light beam trans- itter 2 which is a spectrally scanning, electromagnetic, coherent light source, is controlled by a reference inter- ferometer 9, which in accordance with the invention has high finesse.
  • the reference interferometer 9 coacts with a detector 17, which is, in turn, connected to a start/stop circuit 18.
  • a reference interferometer 9 there may be used, alternatively, a gas spectrum, in order to give rise to the dispersive characteristics from which a wave number interval can be determined.
  • An arrangement for this pur- pose will include a reference cell which is filled with an atomic or molecular gas that has absorption frequencies in the working range of the laser.
  • the reference spectrum can be programmed into a computer which is programmed to control the laser wave number on the basis of the refer- ence signal.
  • a reference interferometer with which the wave number change of the laser can be monitored and determined is an optical reference cavity, which may, for instance, consist of a thin high-finesse etalon or a confocal mirror arrangement that comprises two mutually facing concave mirrors, each of which has its mirror radius located on the opposite mirror.
  • the respective distances between these fringes will constitute a measurement of the evaluated discrepancy. It shall also be possible to cause the beam transmitter 2 to change its wave number during said time section as a continuous (linear) function with respect to time, and also to be able to give the wave number change a sawtooth or a triangular shape.
  • discrepancy * need not solely be used to measure geometric distances, but can also be used to determine prevailing temperatures. For instance, if it is assumed that, the optical path 4, 5, 6 and 7 consists of an optical fibre, a change in temperature will result in a change in length of the fibre which, in turn, will result in a discrepancy change.
  • FIG. 2 illustrates the shape of the light beam 19 ob ⁇ tained from the high-finesse reference interferometer 9.
  • ⁇ is equal to c/2ns
  • ⁇ is equal to c/4ns
  • c is the speed of light
  • n is the refractive index in the reference interferometer
  • s is the geometric flat distance
  • a reference interferometer e.g. an eta ⁇ lon, that has a free spectral range of 5 cm " (150 GHz).
  • the counter value will be equal to the distance measured, in millimeters. This numerical value can therefore be sent immediately to a display, without needing to be processed a ithmetically.
  • the etalon used in this example is an air etalon, it will require a thickness of one millimeter.
  • the working function of the reference interferometer can be illustrated with the following concrete example, in which the true distance to be measured is 9 1/3 meters.
  • the optical wavelength of the reference light (beam) will have been taken into account when constructing the dis ⁇ tance measuring apparatus used, such that a specific point on the - ' arrangement will constitute a zero point when determining or measuring distances. This point will, at the same time, constitute the pivot centre in horizontal and vertical directions, so that the arrangement is able to produce data for describing space in polar coordinates, with the aid of angle sensors herefor.
  • s_ of a reference interferometer can be measured with the aid of equation (3) when measuring a distance d. of known value. This calibration value of s. can then either be used in conjunction with subsequent measur- ing operations or s_ can be adjusted to an even number, by rotating the reference interferometer away from the opti ⁇ cal axis, such that its effective s-value will change in accordance with
  • s 1 s/cos ⁇ where ⁇ is the angle between the optical axis and the normal vectors of the interferometer plates.
  • the aforedescribed distance measuring apparatus is able to operate without a retro- reflector at the point from which a distance is measured, even in the case of long distances where the time co ⁇ herence becomes the limiting factor.
  • An optical narrow-band detector system may then be necess ⁇ ary, so as to avoid detection saturation as a result of background illumination.
  • the signal contribution from the weak and diffuse reflected light beam is multiplied by the interference with the reference light beam (see equation 1).
  • the signal compo- nent can be 1 ⁇ W for an object intensity as small as 2.5 x 10 ⁇ W; this is only true when the coherence surface area covers the whole detector.
  • Space coherence can be realized by focusing the laser beam onto the measuring point (which can be done automatically) and by making the receiver aperture as small as the dia ⁇ meter of the beam transmitted. Diffraction from the re ⁇ flecting measuring point will then guarantee that the coherence surface area on the fringe detector will be sufficiently large and, at the same time, that the in ⁇ tensity of the laser beam is utilized to an optimum (the laser is assumed to oscillate in the fundamental mode
  • the speed at which distances can be measured with the above discussed inventive arrangement is not limited by the beam source and its modulation, since in the case of a diode laser it is possible to achieve sweep speeds as high as 5 cm per microsecond with the aid of primitive means. Consequently, this time limitation lies instead in the inertia of the fringe detection system.
  • the optimum measuring time in the case of low and high resolution measuring processes will be 5 microseconds and 100 microseconds respectively when using a 200 MHz detection system.
  • the light beam source - seen spectrally - can also be easily stopped and locked to a fixed beam wave-number, determined by the reference cell and its resonance fre ⁇ quencies.
  • This converts the distance measuring apparatus to a high resolution Michelson laser-inter erometer, with all its possibilities.
  • the interferometer can then be used as a Doppler veloci- meter and vibration analyser. Combinations of this measuring mode and the spectral sweeping measuring mode may be relevant in the case of certain applications.
  • the diode laser is operated with low-voltage electronic devices and can therefore be readily controlled with the aid of a microprocessor, which is operated with software programmed with the user-determined functions in accord ⁇ ance with the method described here.
  • the distance to be measured need not necessarily be a geometric distance, but may equally as well be the length of an optical fibre, either in part or as a whole.
  • Sensors which are intended to detect temperature, pressure or some other magnitude and which are able to influence the optical wavelength in the fibre, either directly or indirectly, can be used advantageously as an interferometer.
  • Either the optical path travelled by the object beam will consist of a single fibre, which in this case will form the sensor totally, or the reference beam may also be transported through a fibre.
  • the two fibres may either be identical to one another, but placed in two mutually separate physical environments which are to be compared, or may be mutually different (e.g. in length) and placed in one and the same physical environ- ment. to function as a calibrated probe.
  • This probe will comprise a single, long single-mode fibre which transports the laser beam from the transmitter to the object whose distance is to be measured (this distance may be in the order of miles).
  • the fibre is joined together with a fibre stump or slug, the length or construction of which decides the sensitivity of the sensor.
  • the beam re ⁇ flected from the join can then be the reference beam and the beam reflected from the stump end the object beam, both of these beams being transported back along the long fibre to the transmitter, where they are detected.
  • the sensitivity of the sensor is determined once and for all during its manufacture. Such sensors, however, are normally too sensitive to be used in different contexts.
  • the sensivity of the same sensor can be reduced dynamically down to a suitable or appropriate level, as required.
  • Figure 3 illustrates schematically one embodiment of the electrical control and detection system utilized in the interference distance measuring apparatus illustrated in Figure 1.
  • no quotient is formed between the result from the units 10, 11 in the measuring section of the interference distance meter, and neither is any reference interference frequency engendered. Instead, a well defined wave-number sweep number is taken as a reference.
  • a thin high-finesse etalon e.g. an etalon having a free spectral range of 3 cm (1.6 mm air gap or 1 mm solid glass) is able to define the measuring sweep interval to one part in 100 000. This is roughly what is required to take full • advantage of a fixed digital distance resolution of, e.g. 0.2 mm in a measuring range of, e.g.
  • the detecting system has a high ampli ⁇ fication over a narrow band width centred on a fixed frequency f (e.g. 15 MHz). Consequently, the laser sweep system is constructed to tune the wave number to a speed which is determined strictly by the incoming object signal.
  • the interference fre ⁇ quency is contingent on the wave-number sweep velocity dk/df and also on each object movement component along the laser beam dx/dt. Consequently, the total number of fringes counted during the time ⁇ t taken to tune the laser to the predetermined wave number interval ⁇ k will be
  • N 2d ⁇ k + 2kv ⁇ t (5)
  • N 2d . ⁇ k + 2kv N/f .
  • the effect of the linear object movement v can be sepa ⁇ rated from the effect of the sweep rate dk/dt, by carrying out two consecutive measurements with the sweep rate sign reversed. If it is assumed that the total number of fringes in the two consecutive sweeps is N- and N at equal wave number intervals ⁇ k. the equation (6) will give
  • N 2d . ⁇ k/(l-2kv/f ) (6)
  • N 2d . ⁇ k/(l+2kv/f ) (7)
  • At least two equations which can be suitably combined for calculating both the distance to the object and also possible movement of the object can then be compiled by carrying out and combining at least two of the following measuring procedures:
  • the fringe pattern on the detector is held stable, by changing the absolute frequency of the laser so as to maintain this stability and the time is measured during a given wave number interval.
  • the laser 30 is, for instance, of the same kind as that used in a laser printer and the intensity of the laser is modulated con- stantly by a current delivered by a voltage controlled oscillator (VCO) 31 which generates a triangular wave shape.
  • VCO voltage controlled oscillator
  • the diagram A at the bottom of Figure 3 illustrates the radiance shape of the transmitted, laser beam in the time domain.
  • the fundamental oscillating frequency of the oscillator 31 is set to a value which is higher than the highest expected repetition frequency, e.g. 15 kHz.
  • the mean laser intensity is controlled by an automatic power control (APC) 32 with the aid of the laser intensity detector 33 found in present day standard diode-type lasers.
  • APC automatic power control
  • the Figure 3 embodiment also includes a microprocessing unit (MPU) 34, which is divided into several blocks in this illustration, all of which are identified by the same reference numeral, since they represent one and the same unit.
  • the microprocessor has an input which receives from the laser head 48 a signal which represents the tempera ⁇ ture of said head and which steers a laser temperature drive means 45 for servo-regulating a Peltier-element 46 on the laser head.
  • the micro- processor (MPU) 34 seeks a continuous sweep area which is free from any laser mode jump, with the aid of a mode jump detector 35. This is effected by adjusting the laser temperature ther oelectrically, until a mode jump is localized in the region of the minimum drive current.
  • the mode jump detector 35 is corre ⁇ sponded by the photo-current emanating from a detector which belongs to a glass etalon of low finesse and a thickness of less than one millimetre. Each mode jump will register as an abrupt discontinuity in this current, which is detected upon passing through a high-pass filter.
  • Diagram B at the bottom of Figure 3 illustrates an example of this current prior to filtration.
  • the mode jump is represented by the pulse-like parts, which are negative in the diagram but which in other cases may be positive.
  • the time constant for this stabilization of temperature through mode jump localization is of the order of magni ⁇ tude of seconds.
  • VCO-signal arriving from block 31 The deviation signal in the circuit 36 rotates a galvanometer, which tilts the etalon.
  • the time constant in this feedback circuit is in the order of magnitude of seconds.
  • phase-locking loop modifies the laser sweep frequency, such as
  • the output signal from the phase locking loop 38 is amplified in an amplifier 39 and steers the voltage controlled oscillator 31.
  • the high fundamental oscillating frequency of the . oscillator 38 will ensure that the interference frequency of the object beam will pass the 15 MHz range. When this takes place, and provided that the signal/noise ratio is
  • phase-locked loop 38 will lock and regulate the frequency of the oscillator 31, by feedback through the FM-input of the oscillator.
  • phase-locked loop 38 will lose the track and the procedure is repeated.
  • phase-locked loop 38 is locked, which state is indicated by a locking indicator circuit 47, a signal (from the circuit 47) is fed to the microprocessor 34 which, in turn, sends a clear-signal to a counter 40.
  • a signal from the circuit 47
  • the microprocessor 34 which, in turn, sends a clear-signal to a counter 40.
  • This is supplied with an output signal from an oscillator 44 of relatively high frequency, e.g. 120 MHz.
  • the choice of frequency is not critical, but the higher the better.
  • The- upper frequency limit is governed by the ability of the counter to count the pulses emanating from the oscil ⁇ lator 44.
  • the counter 40 does not begin to count imme ⁇ diately after receiving a clear-signal from the MPU 34, but waits in readiness for receipt of a start signal from the logic 43, whereupon it begins to count.
  • the oscillator is intended to function as a clock signal generator of high resolution. It is this oscillator which controls the apparatus and which is responsible not only for control of the wave number interval, but " also simul- taneous control of the time.
  • the comparator level for the high-finesse etalon signal follows the laser intensity form for a precise determina ⁇ tion of the measuring wave number interval. Due to the presence of the etalon-centering system, a stop pulse from a start/stop logic circuit 43 in the end-of-count interval will always reach the counter 40 before the end-of-sweep of the voltage steered oscillator 31. This stop pulse will activate the data transfer to the microprocessor 34, in which the accepted sweeps are stored for further process ⁇ ing and for calculating mean values on the basis of the equations (8) and (9) above.
  • each wave number sweep is also possible to divide each wave number sweep into a number of intervals, by selecting a corresponding, thicker high-finesse etalon.
  • the advantage afforded by such a solution is obvious, in those instances when the detection, signals are weak and the phase-locked loop 38 is un ⁇ successful in locking over the entire sweep. Small parts can still be used and sampled, when the wave number markings lie close together.
  • the smaller the free spectral range of the etalon the more defined are the etalon transmission trigger points in the wave number domains. ' .
  • the costs of manufacturing an inventive distance measuring apparatus can be kept low. This is because the interfero ⁇ meter is based on ready-to-use mass produced components.
  • the transmitter including laser, collimator, beam splitter and quarter ( ./4) wavelength plates may be the same as those used in a CD-player. If audiofrequencies can be accepted for fringe detection, it is actually possible to use a complete CD-player, including its detector system with quadrant detector for servo-control of automatic focusing, automatic preamplification level of the audio switching signal for optimum digitilization of, in this case, interference fringes instead of CD-etched hole in ⁇ formation. Otherwise, more advanced receiver units with conversion to standard TTL-pulses are available in the telecommunication field. A simple microprocessor can be used to control the system.
  • the potential fields of use of the invention are innumer ⁇ able, due not least to the low manufacturing price that can be achieved. Available instruments can be either too expensive, too bulky or too accurate for certain applica ⁇ tions.
  • One large field in which the inventive concept can be applied is that of surveying or assaying old buildings, e.g. for reconstruction and the like.
  • a "laser radar" connected to a CAD-system would be able to produce basic drawing data within an hour, whereas a present day firm of architects might take a week.
  • the speed at which the laser interferometer operates also enables the inventive system to be used for industrial process control purposes and for assembly line product control purposes.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Optical Radar Systems And Details Thereof (AREA)

Abstract

La présente invention se rapporte à un procédé et à un appareil servant à mesurer une distance optique à l'aide d'un émetteur de faisceau lumineux (2), qui produit un faisceau électromagnétique cohérent continu, au moins pendant une opération de mesurage. Le faisceau est divisé et transmis le long de deux trajectoires de faisceau (3, 4, 8, 7 et 3, 4, 5, 6, 7) et les deux faisceaux sont réunis au niveau d'un détecteur (10), où ils s'ajoutent l'un à l'autre. L'émetteur (2) est amené à modifier son nombre d'ondes dans le temps pendant au moins une séquence, de façon à déterminer un écart entre les deux trajectoires des faisceaux. Un déphasage correspondant à un nombre d'ondes instantané est enregistré dans un signal de sortie provenant du détecteur (10). On obtient une mesure de ce déphasage, et par conséquent de l'écart, en mesurant le nombre de franges d'interférences occurrentes dans un compteur (10) et/ou en mesurant le temps s'écoulant pendant une séquence donnée. La variation du nombre d'ondes du faisceau transmis par l'émetteur (2) est sélectionnée à l'intérieur d'un intervalle de nombres d'ondes prédéterminé délimité avec précision. L'écart est déterminé sur la base de la dépendance du changement de phase par rapport au temps et/ou à la variation du nombre d'ondes.
PCT/SE1989/000009 1988-01-14 1989-01-13 Procede et appareil servant a effectuer des mesures d'une distance optique Ceased WO1989006781A1 (fr)

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SE8800097A SE460382B (sv) 1988-01-14 1988-01-14 Foerfarande foer att faststaella en upptraedande diskrepans mellan tvaa optiska vaegstraeckor samt anordning anpassad foer utfoerande av foerfarandet
SE8800097-1 1988-01-14

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6934035B2 (en) 2001-12-18 2005-08-23 Massachusetts Institute Of Technology System and method for measuring optical distance
US7365858B2 (en) 2001-12-18 2008-04-29 Massachusetts Institute Of Technology Systems and methods for phase measurements
WO2009009801A1 (fr) 2007-07-12 2009-01-15 Volcano Corporation Appareil et procédés permettant la synchronisation d'échantillons de fréquence uniforme
US7557929B2 (en) 2001-12-18 2009-07-07 Massachusetts Institute Of Technology Systems and methods for phase measurements
JP2015513086A (ja) * 2012-03-01 2015-04-30 ライカ ジオシステムズ アクチエンゲゼルシャフトＬｅｉｃａ Ｇｅｏｓｙｓｔｅｍｓ ＡＧ 干渉計を用いて距離変化を算定するための方法
US9596993B2 (en) 2007-07-12 2017-03-21 Volcano Corporation Automatic calibration systems and methods of use
DE102014105456B4 (de) * 2014-04-16 2020-01-30 Minikomp Bogner GmbH Verfahren zur Vermessung der Außenkontur von dreidimensionalen Messobjekten und zugehöriges Messsystem

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APPLIED OPTICS, Vol. 26, No. 21, issued November 1987, A.J. DEN BOEF, "Interferometric laser rangefinder using a frequency modulated diode laser", see pages 4545-4550. *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6934035B2 (en) 2001-12-18 2005-08-23 Massachusetts Institute Of Technology System and method for measuring optical distance
US7365858B2 (en) 2001-12-18 2008-04-29 Massachusetts Institute Of Technology Systems and methods for phase measurements
US7557929B2 (en) 2001-12-18 2009-07-07 Massachusetts Institute Of Technology Systems and methods for phase measurements
US9528817B2 (en) 2001-12-18 2016-12-27 Massachusetts Institute Of Technology Systems and methods for phase measurements
WO2009009801A1 (fr) 2007-07-12 2009-01-15 Volcano Corporation Appareil et procédés permettant la synchronisation d'échantillons de fréquence uniforme
EP2171396A4 (fr) * 2007-07-12 2016-05-11 Volcano Corp Appareil et procédés permettant la synchronisation d'échantillons de fréquence uniforme
US9596993B2 (en) 2007-07-12 2017-03-21 Volcano Corporation Automatic calibration systems and methods of use
JP2015513086A (ja) * 2012-03-01 2015-04-30 ライカ ジオシステムズ アクチエンゲゼルシャフトＬｅｉｃａ Ｇｅｏｓｙｓｔｅｍｓ ＡＧ 干渉計を用いて距離変化を算定するための方法
US9638519B2 (en) 2012-03-01 2017-05-02 Leica Geosystems Ag Method for determining a change in distance to a movable and reflective target by means of interferometer to determine if the movement of the reflective target is really executable
DE102014105456B4 (de) * 2014-04-16 2020-01-30 Minikomp Bogner GmbH Verfahren zur Vermessung der Außenkontur von dreidimensionalen Messobjekten und zugehöriges Messsystem

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SE8800097D0 (sv) 1988-01-14
SE460382B (sv) 1989-10-02

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