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WO1992014115A1 - Procede et appareil servant a determiner le sens de deplacement de la surface d'un objet - Google Patents

Procede et appareil servant a determiner le sens de deplacement de la surface d'un objet Download PDF

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Publication number
WO1992014115A1
WO1992014115A1 PCT/GB1992/000186 GB9200186W WO9214115A1 WO 1992014115 A1 WO1992014115 A1 WO 1992014115A1 GB 9200186 W GB9200186 W GB 9200186W WO 9214115 A1 WO9214115 A1 WO 9214115A1
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WIPO (PCT)
Prior art keywords
beams
scattered
object surface
coherent light
light
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Ceased
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PCT/GB1992/000186
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English (en)
Inventor
Vincent Toal
Mairead Rosario Reynolds
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Individual
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Individual
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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
    • G01B9/02097—Self-interferometers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/161—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by interferometric means
    • G01B11/162—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by interferometric means by speckle- or shearing interferometry
    • 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
    • G01B9/02094—Speckle interferometers, i.e. for detecting changes in speckle pattern
    • 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
    • G01B2290/70—Using polarization in the interferometer

Definitions

  • the present invention relates to a method and apparatus for determining direction of displacement of an object surface using an interferometer.
  • the invention also relates to a method and apparatus for determining displacement of the object surface.
  • Interferometers are commonly used for determining displacement of an object.
  • a beam of coherent light is directed at a surface of the object and first and second speckle patterns are formed and superimposed one on the other to form a speckle interference pattern.
  • a single speckle of the speckle interference pattern is observed and the cyclic variation in intensity of the speckle due to phase change between the first and second patterns resulting from displacement of the surface gives a measure of the distance moved by the object surface, namely, the displacement of the object surface.
  • a pair of beams of coherent light are directed at the same area of the object surface and scattered.
  • the scattered beams are combined to form an interference pattern and a single speckle of the interference pattern is observec.
  • the number of cyclic variations in intensity of the observed speckle is counted, and the count is proportional to the in-plane displacement of the object surface.
  • one beam of coherent light is directed at the object surface and scattered, while a second beam of coherent light is directed at a reference surface and scattered.
  • Light scattered from the object and reference surfaces is combined to form a speckle interference pattern.
  • the out-of-plane displacement is determined.
  • the count of cyclic variations is proportional to the out-of-plane displacement.
  • One object of the invention is to provide a method and apparatus for determining direction of displacement of an object surface. Another object of the invention is to provide a method and apparatus for determining direction of displacement of an object surface which is relatively simple and easy to construct and use. A further object of the invention is to provide a method and apparatus for determining direction of displacement of an object surface which is relatively economical to construct and use.
  • the component to be phase shifted in the one of the secondary scattered beams is phase shifted relative to another component in that secondary scattered beam.
  • the component to be phase shifted in the one of the secondary scattered beams is phase shifted relative to a component in the other secondary scattered beam.
  • the phase shifted component of the secondary scattered beam is phase shifted through approximately 90°. It will of course be appreciated that the phase shifted component may be phase shifted through substantially any angle, provided it is not phase shifted through 180°.
  • each secondary scattered beam is polarised prior to detecting the direction of the resultant phase shift of the speckle interference patterns.
  • the direction of the resultant phase shift between the speckle interference patterns is detected by observing a single speckle of the respective speckle interference patterns.
  • the same speckle is observed in each speckle interference pattern.
  • the combined first and second primary scattered beams are passed through a restricting means for permitting the passage of only one speckle therethrough prior to splitting the combined beam to form the secondary scattered beams.
  • the component of light to be phase shifted is phase shifted in one of the secondary scattered beams after the combined beam has been split.
  • the component of light to be phase shifted is phase shifted prior to scattering of the said first or second primary scattered beam.
  • the first and second primary scattered beams are scattered from the object surface for determining the direction of in-plane displacement.
  • the first and second primary scattered beams are scattered from the same area on the object surface.
  • the first and second primary scattered beams are derived from respective beams of coherent light directed at the object surface.
  • each beam of coherent light is directed at the object surface at an angle of incidence in the range of 0° to 70°.
  • each beam of coherent light is directed at the object surface at an angle of incidence in the range of 0° to 30°.
  • each beam of coherent light is directed at the object surface at an angle of incidence of approximately 20°.
  • two factors must be considered. Firstly, if the angle of incidence is too small, a large displacement of the object surface is required to obtain a single cyclic variation of a speckle of a speckle interference pattern, and accordingly, the sensitivity of the apparatus to displacement is affected. While on the other hand, if the angle of incidence is too large, depolarisatior.
  • depolarisation has been found to be only 2%, which considerably improves the reliability of the apparatus in determining direction of displacement. It is, however, believed that an angle of incidence of up to 70° would be acceptable where light of wavelength of 10.6 microns is used.
  • Such light may be derived from a carbon dioxide laser source.
  • the angle of incidence at which each beam of coherent light is directed at the object surface is the same. It has been found desirable to maintain the angle of incidence of both beams of coherent light equal so that the apparatus is sensitive to displacement in one direction only. Where the angles of incidence are not equal, it has been found that results from the apparatus may be influenced by displacement of the object surface in a plane other than its own plane.
  • the component of light to be phase shifted is phase shifted in one of the beams of coherent light prior to reaching the object surface.
  • one of the first and second scattered beams is scattered or reflected from a reference surface for determining the direction of out-of-plane displacement of the object surface, the first and second scattered beams being formed by directing respective beams of coherent light at the object and reference surfaces.
  • the beams of coherent light are incident at approximately 90° to the respective surfaces.
  • at least one of the respective object and reference surfaces is optically rough.
  • the reference surface is optically smooth.
  • the two beams of coherent light are derived from the same source, a main beam of coherent light from the source being split to form the said two beams.
  • tne main beam of coherent light is plane polarised.
  • the main beam of coherent light is derived from a laser light source.
  • the beam of coherent light is derived from a helium neon laser light source.
  • the two beams of coherent light are plane polarised.
  • the plane of polarisation of one of the beams of coherent light is at 90° relative to the plane of polarisation of the other beam of coherent light.
  • the planes of polarisation of the beams of coherent l ght are sim lar.
  • the optical path difference between the two beams of coherent light is substantially constant when determining the direction of in-plane displacement.
  • the method further comprises the step of counting the number of cyclic variations in intensity in a speckle interference pattern for determining the displacement of the object surface.
  • the method further comprises the step of counting the number of cyclic variations in intensity in the speckle interference pattern in a predetermined period of time for determining the speed of displacement of the object surface.
  • the invention provides apparatus for determining the direction of displacement of an object surface, the apparatus comprising an interferometer of the type comprising means for directing a beam of coherent light at the object surface and means for forming a speckle interference pattern by combining first and second primary scattered beams, at least one of the said primary scattered beams being scattered from the object surface wherein the apparatus further comprises secondary splitting means for splitting the combined scattered beam into two secondary scattered beams so that each secondary scattered beam comprises at least one component of light of each of the first and second primary scattered beams, phase shifting means for phase shifting one of the components of light of one of the secondary scattered beams relative to another component of light of that secondary scattered beam or relative to one of the components of light of the other secondary scattered beam, and detecting means for detecting the direction of the resultant phase shift of the speckle interference pattern of one of the secondary scattered beams relative to the speckle interference pattern of the other secondary scattered beam for determining the direction of displacement of the object surface.
  • an interferometer of the type comprising means for directing a beam of coherent light at the object surface and
  • the phase shifting means phase shifts a component in one of the secondary scattered beams relative to another component in that secondary scattered beam.
  • phase shifting means phase shifts a component in one of the secondary scattered beams relative to a component in the other secondary scattered beam.
  • the phase shifting means phase shifts the component of light to be phase shifted through an angle of approximately 90°.
  • the means for forming the speckle interference patterns comprises a pair of secondary plane polarising means for plane polarising each of the secondary scattered beams.
  • one of the secondary plane polarising means is mounted intermediate the phase shifting means and the detecting means.
  • restricting means for permitting the passage of only one speckle of the speckle interference pattern to the detecting means.
  • the restricting means is mounted intermediate the secondary splitting means and the object surface.
  • the means for directing a beam of coherent light at the object surface comprises first and second directing means fo*- directing a pair of beams of coherent light at the object surface.
  • the first and second directing means direct the beams of coherent light at the same area on the object surface.
  • the two beams of coherent light are derived from a main light source means.
  • the main light source means provides a main beam of plane polarised coherent light.
  • primary beam splitting means is provided for splitting the main beam of coherent light into the two beams of coherent light.
  • the phase shifting means is provided in the path of one of the beams of coherent light before the said beam of light reaches the object surface.
  • a reference surface is provided, and the directing means comprises first and second directing means, the first directing means directing a beam of coherent light at the object surface and the second directing means directing a beam of coherent light at the reference surface.
  • one of the respective object and reference surfaces is optically rough.
  • the reference surface is optically smooth.
  • means for combining the first and second primary scattered beams combines the first primary scattered beam scattered from the object surface and the second primary scattered beam scattered or reflected from the reference surface.
  • the detecting means comprises a pair of photoelectric transducers for receiving the respective secondary scattered beams, and signal analyzing means for receiving and analyzing electronic signals received from the photoelectric transducers for determining the direction of the resultant phase shift between the speckle interference patterns of the respective secondary scattered beams.
  • the apparatus further comprises means for counting the number of cyclic variations in intensity in a speckle interference pattern for determining displacement of the object surface.
  • the means for determining the number of cyclic variations in intensity in the speckle interference pattern counts the number of cyclic variations in a predetermined period of time for determining the speed of displacement of the object surface.
  • a particularly important advantage of the invention is that it provides a method and apparatus for determining the direction of displacement of an object surface. In certain embodiments of the invention, the method and apparatus also determines the displacement of the object surface.
  • a particularly important advantage of the invention is that it provides a method and apparatus for determining the displacement of an object surface which is relatively simple and easy to construct and use.
  • Another important advantage of the invention is that it provides a method and apparatus for determining direction of displacement of an object surface which is relatively economical to construct and use.
  • the apparatus according to the invention is also less prone to error than apparatus known heretofore.
  • the apparatus also permits a relatively low cost light source means to be used.
  • Fig. 1 is a schematic representation of apparatus according to the invention for determining displacement and direction of displacement of an object surface
  • Fig. 2 is a schematic representation of apparatus according to another embodiment of the invention for determining displacement and direction of displacement of an object surface
  • Fig. 3 is a schematic representation of apparatus according to a further embodiment of the invention for determining displacement and direction of displacement of an object surface.
  • FIG. 1 there is illustrated apparatus according to the invention indicated generally by the reference numeral 1 for determining both displacement and direction of displacement of an optically rough object surface 2.
  • the apparatus is for determining in- plane displacement of the object surface 2, namely, displacement in the directions of the arrows A and B.
  • the apparatus 1 operates substantially on the principle of an interferometer, and in describing the apparatus 1, it will be assumed that the reader understands the operation of an interferometer.
  • the apparatus 1 comprises a main light source means, in this embodiment of the invention, an unexpanded helium neon laser light source 3 of output power 10 mW.
  • the light source 3 projects a substantially parallel main beam MB of circular cross section of coherent laser light at a primary beam splitting means, namely, a primary beam splitter 5 comprising a lossy beam splitter.
  • the main beam MB is polarised in the vertical plane, namely, in a plane normal to the page of the drawing.
  • the primary beam splitter 5 splits the main beam MB into two beams of coherent laser light, namely, a first beam Bl and a second beam B2.
  • the primary beam splitter 5 acts as a first directing means and directs the first beam Bl at an area 7 of the object surface 2 at an angle of incidence Q 1 to the normal to the object surface 2.
  • the plane of polarisation of the first beam Bl is unaltered by the primary beam splitter 5, in other words, the plane of polarisation of the first beam Bl is polarised in the vertical plane.
  • the second beam B2 passes through the primary beam splitter 5 also polarised in the vertical plane, and is passed through a primary plane polarisation means, namely, a primary half wave plate 9 whose fast axis is at an angle of 45° to the vertical for turning the plane of polarisation of the second beam B2 through 90°.
  • Second directing means for directing the second beam B2 at the object surface 2 comprises a reflector 10 which reflects the beam B2 to the same area 7 of the object surface 2 at which the first beam Bl is incident.
  • the reflector 10 directs the second beam B2 at the area 7 of the object surface 2 at an angle of incidence ⁇ 2 to the normal to the object surface 2, which in this embodiment of the invention is equal to ⁇ In this case, ⁇ 1 _an.d. ⁇ 2 are 20°.
  • the reflector 10 does not alter the plane of polarisation of the beam B2.
  • a first primary scattered beam Rl and a second primary scattered beam R2 which are derived respectively from the first and second beams Bl and B2 which are scattered by the object surface 2 combine to form a combined beam which passes along the normal from the object surface 2 to a secondary beam splitting means, namely, a secondary beam splitter 14 comprising a lossy beam splitter.
  • the secondary beam splitter 14 splits the combined first and second primary scattered beams Rl and R2 into a pair of secondary scattered beams, namely, a first secondary scattered beam SB1 and a second secondary scattered beam SB2 both of which will be described below.
  • the first and second primary scattered beams Rl and R2 remain polarised after being scattered and remain polarised in the same plane of polarisation as their respective corresponding first and second beams Bl and B2. Accordingly, the first and second primary scattered beams Rl and R2 are orthogonally plane polarised relative to each other and do not interfere with each other.
  • the combined first and second primary scattered beams Rl and R2 are split in the secondary beam splitter 14 so that each of the first and second secondary scattered beams SB1 and SB2 comprise the first and second primary scattered beams Rl and R2.
  • each secondary scattered beam SB1 and SB2 has a vertical and horizontal component of light derived respectively from the first and second primary scattered beams Rl and R2.
  • the f rst and second secondary scattered beams SB1 and SB2 are directed at detecting means, which in this case comprises a pair of first and second photoelectric sensitive transducers 20 and 21, the purpose of which is described below.
  • the first secondary scattered beam SB1 is directed at the first transducer 20 through a means for forming a speckle interference pattern, which is provided by a first secondary plane polarising means, namely, a first plane polarising plate 24.
  • the transmission axis of the first plane polarising plate 24 is at 45° to the two planes of polarisation of the first and second primary scattered beams Rl and R2 for forming a speckle interference pattern by combining the first and second primary scattered beams Rl and R2 in the first secondary scattered beam SB1.
  • the speckle interference pattern is received by the first transducer 20.
  • the second secondary scattered beam SB2 is reflected through 90° from a reflector 25 and passed through a phase shifting means for phase shifting one of the components of the light in the second secondary scattered beam SB2 through 90° relative to the other component in that secondary scattered beam SB2.
  • the phase shifting means comprises a quarter wave plate 28 whose fast axis is parallel to the plane of polarisation of one of the components of light of the second secondary scattered beam SB2, in this case, the vertical component.
  • the quarter wave plate 28 phase shifts the vertical component through 90° relative to the horizontal component of the second secondary scattered beam SB2.
  • the second secondary scattered beam SB2 passes from the quarter wave plate 28 into a means for forming a speckle interference pattern which is provided by a second secondary plane polarising means comprising a second plane polarising plate 30.
  • the transmission axis of the second plane polarising plate 30 is at 45° to the two planes of polarisation of the first and second primary scattered beam components of the second secondary scattered beam SB2 for forming a speckle interference pattern which is received by the second transducer 21.
  • Restricting means for permitting the passage of only one speckle of a speckle interference pattern to fall on the first and second transducers 20 and 21 comprises a pin hole plate 32 having a pin hole 33 of diameter sufficiently small to permit only a single speckle of a speckle interference pattern to pass therethrough, thereby the transducers 20 and 21 detect the image of the same speckle of the speckle interference pattern.
  • the direction of displacement of the object surface 2 is determined.
  • a change in direction of the object surface 2 causes a change in the direction of the resultant phase shift.
  • the phase of the speckle interference pattern formed by the second secondary scattered beam SB2 leads the speckle interference pattern formed by the first secondary scattered beam SB1
  • the object surface 2 is moving in the direction of the arrow A.
  • the phase of the speckle interference pattern formed by the second secondary scattered beam SB2 lags the speckle interference pattern formed by the first secondary scattered beam SB1
  • the object surface 2 is moving in the direction of the arrow B.
  • the direction of the resultant phase shift (in other words the sign of the phase difference) of the speckle interference patterns of the first and second secondary scattered beams SB1 and SB2 is determined.
  • the means for detecting the direction of the resultant phase shift of the speckle interference patterns, as well as comprising the first and second transducers 20 and 21, also comprises signal analyzing means provided by an electronic analyzing circuit 35 for analyzing electronic signals received from the transducers 20 and 21 and for providing results.
  • the circuit 35 comprises a buffer circuit 34 for delivering the signals from the transducers 20 and 21 to a display unit 36 for displaying the direction of the resultant phase shift.
  • the display unit 36 may be a graph plotter or a cathode ray oscilloscope or other suitable display device, which would give a visual representation of the signals received from the transducers 20 and 21.
  • the direction of the resultant phase shift between the signals received from the transducers 20 and 21 may be visually observed on the display unit 36.
  • the direction of the displacement of the object surface 2 can readily easily be determined.
  • the signals from the transducers 20 and 21 may be fed to further analyzing circuitry (not shown) which would give a numerical indication of the direction of the resultant phase shift.
  • the in-plane displacement of the object surface 2 is proportional to the number of cyclic variations of intensity of the speckle falling on either the first or second transducer 20 and 21. Accordingly, by counting the number of cyclic variations of intensity of the observed speckle, the displacement of the object surface 2 can be determined.
  • the signals from the transducers 20 and 21 are passed to operational amplifier circuits 37 and 38 which amplify the signals.
  • the outputs from the amplifier circuits 37 and 38 are passed to Sch itt trigger circuits 39 and 40 which convert the signals to rectangular pulses which are fed to a dual edge triggered D-type flip flop circuit 41 to provide count up/count down commands to a counter 42 which also receives rectangular pulses from the Schmitt trigger circuit 39.
  • Signals from the counter 42 are delivered to a correlation circuit 43 which correlates the number of counts of cyclic variation of the intensity of the speckle to a corresponding value of displacement of the object surface in either direction of the arrows A or B.
  • the output from the correlation circuit 43 is delivered to a display 44 which displays the displacement of the object surface 2.
  • a timer 45 permits the number of counts from the Schmitt trigger circuit 39 in a predetermined period of time to be counted to enable the speed of displacement of the object surface 2 to be computed. The speed is also displayed on the display 44.
  • the diameter of the pinhole 33 is 650 ⁇ m diameter and the pinhole plate 32 is placed at approximately 680 mm from the object surface 2.
  • optical path difference between the two beams Bl and B2 remains substantially constant during tests, apart from the effect of any slight variations in the surface profile of the object surface 2.
  • FIG. 2 there is illustrated apparatus according to another embodiment of the invention indicated generally by the reference numeral 50 also for determining in-plane displacement and direction of displacement of an optically rough object surface 2.
  • the apparatus 50 in certain respects is similar to the apparatus 1 and similar components are identified by the same reference numerals.
  • the main beam MB from the laser light source 3 is split by the primary beam splitter 5 into first and second beams Bl and B2.
  • the first beam is directed by the primary beam splitter 5 at an area 7 on the object surface 2, while the second beam B2 is reflected by the reflector 10 to the same area 7 of the object surface 2.
  • the angle of incidence of the two beams Bl and B2 to the normal of the object surface 2, namely ⁇ x and ⁇ 2 are equal and equal to 20°.
  • the main beam MB from the l ght source 3 is plane polarised in the vertical plane.
  • the first and second beams Bl and B2 leave the primary beam splitter 5 plane polarised in the vertical plane.
  • Means for altering the plane of polarisation of the first and second beams Bl and B2 comprise a pair of half wave plates 53 and 54, each of which have a fast axis at 22.5 C to the vertical.
  • the half wave plates 53 and 54 rotate the plane of polarisation of the first and second beams Bl and B2 fay 45° so that the plane of polarisation of the first and second beams Bl and B2 leaving the half wave plates 53 and 54 is at 45° to the vertical and horizontal axes.
  • the first beam Bl is passed through a phase shifting means, namely, a quarter wave plate 56, the fast axis of which is vertical.
  • the quarter wave plate 56 phase shifts the vertical component of the beam Bl relative to the horizontal component of the beam Bl. Accordingly, the vertical component of the first beam Bl falls on the object surface 2 out of phase by 90° relative to the horizontal component of the first beam Bl.
  • the beams Bl and B2 are scattered by the object surface 2 and a combined beam comprising first and second primary scattered beams Rl and R2 derived respectively from the beams Bl and B2 is passed to the secondary beam splitter 14.
  • the vertical component of the first primary scattered beam Rl is 90° out of phase with the horizontal component of the first primary scattered beam Rl.
  • the secondary beam splitter 14 splits the combined first and second primary scattered beams Rl and R2 into first and second secondary scattered beams SB1 and SB2.
  • the secondary beam splitter 14 splits the combined scattered beam so that the vertical components of the first and second primary scattered beams Rl and R2 are in the first secondary scattered beam SB1, and the horizontal components of the first and second primary scattered beams Rl and R2 are in the second secondary scattered beam SB2.
  • the first secondary scattered beam SB1 is thus vertically polarised and comprises two vertical components which are derived from the vertical components of the first and second primary scattered beams Rl and R2. Additionally, the vertical components of the first secondary scattered beam SB1 interfere with each other to form a speckle interference pattern.
  • the second secondary scattered beam SB2 is horizontally polarised and comprises two horizontal components which are derived from the horizontal components of the first and second primary scattered beams Rl and R2, which also interfere with each other to form a speckle interference pattern.
  • the vertical component of the first secondary scattered beam SB1 which is derived from the first primary scattered beam Rl is 90° out of phase of the horizontal component derived from the first primary scattered beam Rl in the second secondary scattered beam SB2.
  • a reflector 57 reflects the first secondary scattered beam SB1 onto the first transducer 20 while the second secondary scattered beam SB2 is directed directly to the second transducer 21.
  • the pinhole plate 32 only permits the passage of a single speckle of the speckle interference pattern of the combined primary scattered beams Rl and R2 to pass through to the secondary beam splitter 14, thereby ensuring that only one speckle of the speckle interference pattern falls on the transducers 20 and 21, and each transducer 20 and 21 receives the same speckle.
  • the speckle interference patterns formed by the first and second secondary scattered beams SBl and SB2 are also out of phase by 90°.
  • the direction of displacement of the object surface 2 is determined.
  • the object surface 2 is moving in the direction of the arrow A.
  • the phase of the speckle interference pattern formed by the first secondary scattered beam SBl lags the phase of the speckle interference pattern formed by the second secondary scattered beam SB2
  • the object surface is moving in the direction of the arrow B.
  • Signals from the transducers 20 and 21 are delivered to the circuit 35 which is identical to the circuit 35 of the apparatus 1 for determining the direction of the resultant phase shift for determining the direction of displacement of the object surface 2, and also for determining the displacement and speed of displacement of the object surface 2.
  • FIG. 3 there is illustrated apparatus according to a further embodiment of the invention indicated generally by the reference numeral 60 for determining out-of-plane displacement in the direction of the arrows C and D of an object surface 2 and also for determining the direction of the out-of-plane displacement of the object surface 2.
  • the apparatus 60 while not being identical to the apparatus 1, comprises a number of components which are substantially similar to the apparatus 1, and accordingly, sirilar components are identified by the same reference numerals.
  • the main beam MB of plane polarised laser light polarised in the vertical plane from the light source 3 is delivered to the primary beam splitter 5 through a semi- reflector 61, the purpose of which will be described below.
  • the main beam MB passes through the semi-reflector 61 with its plane of polarisation unaltered.
  • the main beam MB is split in the primary beam splitter 5 into two beams Bl and B2.
  • the primary beam splitter 5 is a lossy beam splitter.
  • the first beam Bl is directed towards an area 7 on the object surface and remains plane polarised in the vertical plane, in other words normal to the plane of the page of the drawing.
  • the second beam B2 is plane polarised in the vertical plane and is directed towards a reference surface 63 which may be rough or smooth.
  • the first and second beams Bl and B2 are incident at right angles on the object surface 2 and reference surface 63, respectively. Light is scattered from the object surface 2 and may be scattered or reflected from the reference surface 63, and remains polarised in the original plane of polarisation of the first and second beams Bl and B2.
  • a first primary scattered beam Rl scattered from the object surface 2 and a second primary scattered beam R2 which may be scattered or reflected from the reference surface 63 are combined in the primary beam splitter 5 and substantially simultaneously split into first and second secondary scattered beams SBl and SB2.
  • the primary beam splitter 14 also acts as a secondary beam splitter.
  • the first secondary scattered beam SBl comprises components of the first and second primary scattered beams Rl and R2 and is directed to the first transducer 20.
  • the second secondary scattered beam SB2 comprises components of the first and second primary scattered beams Rl and R2, and is directed towards the semi-reflector 61.
  • the semi-reflector 61 reflects the second secondary scattered beam SB2 to the second transducer 21.
  • the primary beam splitter 5 phase shifts the components of the first secondary scattered beam SBl relative to each other, and also phase shifts the components of the second secondary scattered beam SB2 relative to each other.
  • the net effect of the phase shifting of the components of the two secondary scattered beams SBl and SB2 is that the first secondary scattered beam SBl is phase shifted through approximately 90° relative to the second secondary scattered beam SB2.
  • a pair of pinhole plates 32 are provided with pinholes 33 of diameter sufficient to permit only a single speckle of the speckle interference pattern to fall on the first and second transducers 20 and 21.
  • the pinhole plates 32 are arranged so that the same speckle is detected by both transducers 20 and 21. It is envisaged in certain cases that a pinhole plate may be provided in the primary beam splitter 5 to further ensure that an image of the same speckle falls on the first and second transducers 20 and 21.
  • the circuit 35 determines whether the direction of the resultant phase shift is leading or lagging.
  • a leading phase shift of the speckle interference pattern formed by the first secondary scattered beam SBl relative to the speckle interference pattern formed by the second secondary scattered beam SB2 indicates out*-of-plane displacement of the object surface 2 in the direction of the arrow C, while a lagging phase shift indicates displacement of the object surface 2 in the direction of the arrow D.
  • any other suitable laser light source may be used. Indeed, in_certain cases, it is envisaged that a laser diode type light source may be used. Further, it is envisaged that light sources other than a laser light source may be provided. Any l ght source which provides a coherent light beam over a sufficient distance which will be well known to those skilled in the art would be suitable. While the light source has been described as providing a beam of circular cross section, a beam of any other cross section may be provided.
  • any other suitable beam splitters may be used. Indeed, it is envisaged in certain cases that the primary beam splitter may be dispensed with if a pair of independent light sources were provided.
  • Other suitable phase shifting means besides quarter wave plates may be used, and in the case of the apparatus of Fig. 3, a phase shifting means independent of the primary beam splitter may be provided for phase shifting one of the secondary scattered beams relative to the other.
  • the apparatus described with reference to Figs. 1 to 3, as well as being used for determining linear displacement and the direction of displacement of an object surface, may also be used for determining the rotational displacement and direction of an object surface.
  • a polarisation preserving fibre-optic light guide may be located with one end on the object surface normal at a distance from the object surface of at least z where z * r w / (1.5 / ⁇ ) with w now the core diameter of the fibre, r the diameter of the illuminated spot on the object surface and ? ⁇ the source wavelength.
  • the fast axis of the fibre at the input end would be set parallel to the plane of polarisation of the laser. This would provide for a compact system.
  • two polarisation preserving fibres may be used, whose input ends would be oriented with their fast axes parallel to the plane of polarisation of the main light beam and located at the object surface normal such that a single speckle more than covers both fibre end faces.
  • the fast axes at the output ends would be oriented each at 45° to the transmission axis of a plane polariser. No beam splitter would be required. If the fibres had the same length, then a quarter wave plate would be needed as before for phase shifting, but this can be removed if the fibres differ in length by a quarter of a beatlength.
  • the light scattered from the object surface along the normal to the object surface may be passed into a polarisation preserving fibre coupler, whose fast axis is parallel to the plane of polarisation of the laser, and whose output fibres differ in length by one quarter of a beatlength, and the quarter wave plate could be dispensed with.
  • a quarter wave plate known as an input quarter wave plate may be inserted between the beam splitter and the object in the apparatus of Fig. 2.
  • the quarter wave plate would have its fast axis parallel to the plane polarisation direction.
  • the plane polarisers and output quarter wave plate can be dispensed with in this arrangement and replaced by a single polarising beam splitter.
  • the apparatus of the invention may, if desired, be enclosed in a housing which would be provided with a relatively small opening or window to allow illumination of the object surface and reception of the scattered beam or beams from the object surface.
  • this provides for the elimination of errors arising from air currents.
  • the object surface or reference surface need be optically rough.
  • one of the object or reference surfaces could be optically smooth.
  • the half wave plate 9 instead of being disposed between the primary beam splitter and the reflector, may be disposed between the reflector and the object surface in the path of the second beam of coherent light B2.

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

Abstract

Un appareil (1) servant à déterminer le sens de déplacement d'une surface (2) dans le même plan, selon le principe de l'interféromètrie, dirige sur la surface (2) deux faisceaux de lumière cohérente (B1) et (B2) qui sont polarisés en un plan orthogonal l'un par rapport à l'autre. Des faisceaux (R1) et (R2) dispersés de la surface (2) sont divisés dans un séparateur de faisceaux (14) en faisceaux secondaires (SB1) et (SB2). Des polarisateurs (24) et (30) polarisent dans un plan les faisceaux (SB1) et (SB2) afin de produire des configurations d'interférence à tachetures sur des transducteurs (20) et (21). Une lame quart d'onde (28) effectue un décalage de phase de l'une des composantes du faisceau secondaire (SB1) de l'ordre de 90° par rapport à l'autre composante du faisceau secondaire (SB1). Un circuit (35) détermine le sens du décalage de phase des configurations d'interférence à tachetures afin de déterminer le sens de déplacement de la surface de l'objet (2).
PCT/GB1992/000186 1991-01-31 1992-01-31 Procede et appareil servant a determiner le sens de deplacement de la surface d'un objet Ceased WO1992014115A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IE32691A IE910326A1 (en) 1991-01-31 1991-01-31 A method and apparatus for detecting direction and¹displacement of a surface
IE326/91 1991-01-31

Publications (1)

Publication Number Publication Date
WO1992014115A1 true WO1992014115A1 (fr) 1992-08-20

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PCT/GB1992/000186 Ceased WO1992014115A1 (fr) 1991-01-31 1992-01-31 Procede et appareil servant a determiner le sens de deplacement de la surface d'un objet

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IE (1) IE910326A1 (fr)
WO (1) WO1992014115A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996029569A1 (fr) * 1995-03-21 1996-09-26 Nederlandse Organisatie Voor Toegepast- Natuurwetenschappelijk Onderzoek Tno Systeme interferometrique et procede de calcul d'un changement de phase entre deux diagrammes d'interference successifs enregistres par paire par ledit systeme interferometrique
WO1998037379A1 (fr) * 1997-02-20 1998-08-27 Microe Capteur de position d'interference de surface diffuse
US20230035415A1 (en) * 2021-07-30 2023-02-02 Svarog LLC Thin films and surface topography measurement using polarization resolved interferometry

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58225304A (ja) * 1982-06-25 1983-12-27 Yokogawa Hokushin Electric Corp 光学式機械量測定装置
JPS59190605A (ja) * 1983-04-13 1984-10-29 Hitachi Ltd 面内変位測定装置
JPS62165104A (ja) * 1986-01-17 1987-07-21 Mitsubishi Heavy Ind Ltd レ−ザスペツクル歪計測装置

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58225304A (ja) * 1982-06-25 1983-12-27 Yokogawa Hokushin Electric Corp 光学式機械量測定装置
JPS59190605A (ja) * 1983-04-13 1984-10-29 Hitachi Ltd 面内変位測定装置
JPS62165104A (ja) * 1986-01-17 1987-07-21 Mitsubishi Heavy Ind Ltd レ−ザスペツクル歪計測装置

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 12, no. 2 (P-652)(2849) 7 January 1988 & JP,A,62 165 104 ( MITSUBISHI HEAVY IND. LTD. ) 21 July 1987 *
PATENT ABSTRACTS OF JAPAN vol. 8, no. 82 (P-268)(1519) 14 April 1984 & JP,A,58 225 304 ( YOKOGAWA DENKI SEISAKUSHO K.K. ) 27 December 1983 *
PATENT ABSTRACTS OF JAPAN vol. 9, no. 54 (P-340)(1777) 8 March 1985 & JP,A,59 190 605 ( HITACHI SEISAKUSHO K.K. ) 29 October 1984 *
stract *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996029569A1 (fr) * 1995-03-21 1996-09-26 Nederlandse Organisatie Voor Toegepast- Natuurwetenschappelijk Onderzoek Tno Systeme interferometrique et procede de calcul d'un changement de phase entre deux diagrammes d'interference successifs enregistres par paire par ledit systeme interferometrique
NL9500546A (nl) * 1995-03-21 1996-11-01 Tno Interferometriesysteem en werkwijze voor het berekenen van een faseverandering tussen opeenvolgende interferentiepatronen die paarsgewijs zijn geregistreerd met dat interferometriesysteem.
WO1998037379A1 (fr) * 1997-02-20 1998-08-27 Microe Capteur de position d'interference de surface diffuse
US20230035415A1 (en) * 2021-07-30 2023-02-02 Svarog LLC Thin films and surface topography measurement using polarization resolved interferometry
US11761753B2 (en) * 2021-07-30 2023-09-19 Svarog LLC Thin films and surface topography measurement using polarization resolved interferometry

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