WO1992020991A1 - Interferometre a coupure dynamique - Google Patents

Interferometre a coupure dynamique Download PDF

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Publication number
WO1992020991A1
WO1992020991A1 PCT/US1992/004025 US9204025W WO9220991A1 WO 1992020991 A1 WO1992020991 A1 WO 1992020991A1 US 9204025 W US9204025 W US 9204025W WO 9220991 A1 WO9220991 A1 WO 9220991A1
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WO
WIPO (PCT)
Prior art keywords
shearing
incident beam
interferometer
wavefront
fringe
Prior art date
Application number
PCT/US1992/004025
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English (en)
Inventor
James J. Snyder
Original Assignee
Blue Sky Research, Inc.
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 Blue Sky Research, Inc. filed Critical Blue Sky Research, Inc.
Publication of WO1992020991A1 publication Critical patent/WO1992020991A1/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
    • G01B9/02097—Self-interferometers
    • G01B9/02098—Shearing interferometers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
    • G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
    • G01J9/0215—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods by shearing interferometric methods
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/02—Testing optical properties
    • G01M11/0242—Testing optical properties by measuring geometrical properties or aberrations
    • G01M11/0271—Testing optical properties by measuring geometrical properties or aberrations by using interferometric methods

Definitions

  • Fizeau a collimated laser beam generated within the instrument is split into two beams, one of which provides a reference surface while the other beam is passed through the test optic set up in such a way that if it were perfect the exiting beam would exactly match the wavefront of the reference beam.
  • the two beams are combined with a beamsplitter and the resulting fringes of constant height represent a contour plot of the wavefront transmitted by the lens.
  • the fringe pattern is captured by a two dimensional detector array (such as a CCD camera) and analyzed by computer to provide various parameters of the performance of the optic and the details of the distortion it causes.
  • a two dimensional detector array such as a CCD camera
  • these instruments are well suited to measuring the quality of optical components, they are not able to directly measure the wavefront of a beam. Moreover, if the test wavefront deviates significantly from the reference wavefront, so that the fringe spacing approaches the pixel size anywhere, then the instrument is unable to correctly interpret the fringe pattern.
  • a different type of interferometer is available from Wyko for direct measurement of the wavefront of a nearly collimated laser beam. This interferometer is a self-referenced Mach-Zehnder with equal optical path lengths.
  • the referenc beam is focussed through a pinhole spatial filter to remove all wavefront aberrations and the remaining spherical wave is collimated by a lens.
  • the test and reference beams travel the same total distance before being recombined at a beamsplitter, so that laser sources with short coherence lengths can be utilized.
  • the fringe pattern of the self- referenced Mach-Zehnder is essentially similar to the fring patterns produced by the other forms of interferometers, an it is recorded and interpreted in the same way.
  • the instrument can also be used to measure optics by measuring the wavefront of a beam from a test optic which would have produced a collimated output beam if the optic were perfect. For example, if a test lens were illuminated by a point source located at its focal point, the transmitted beam would be collimated if the lens were free of aberrations.
  • phase shift interferometry offers substantially better signal-to noise ratio in the phase measurement and in addition provides a uniform grid of phase data that is independent of the number of fringes.
  • interferometer is the lateral shearing plate interferometer.
  • This instrument typically consists o an uncoated glass plate with flat surfaces. Some implementations have parallel surfaces, and some have a small angle (wedge) between the surfaces.
  • shearin interferometers are very compact, they are self-referencing and the interfering rays travel common or nearly common paths, so that they are relatively insensitive to alignment vibration, or air turbulence. These features favor the use of shearing interferometers for laboratory and industrial applications.
  • Lateral shearing interferometers are commonly used for measuring the wavefront shape of a laser beam. If the shearing plate is wedged, the lateral shearing interferometer is sometimes referred to as a Fizeau interferometer, which, with the proper orientation of the wedge, can be used to measure the wavelength of the laser beam as well as the wavefront shape.
  • the shearing interferometer is placed at an angle relative to the incident beam to be characterized and two reflections of the incident beam result.
  • One reflection is from the front surface of the glass plate and the other is from the back surface. (Other multiple reflections also occur between the surfaces before they exit the front surface. These multiply reflected beams are, however, much lower in intensity than the two principal beams described, and hence will be ignored in the ensuing analysis.)
  • These two reflected beams from the front and rear surfaces interfere where they overlap. For non-normal incidence light, the reflected beams are displaced transversely from each other, so that the fringe pattern in the region of overlap is due to the interference of the wavefront with a sheared version of itself.
  • the resulting fringes of constant slope are analyzed to determine the fringe phase, which corresponds to a one-dimensional derivative of the wavefront.
  • the wavefront shape is found by integrating the wavefront derivative along the shear direction.
  • a screen o other plane, opaque, surface placed in the path of the reflected beams will show the transverse displacement of th optical axes of two beams, hereinafter called the lateral shear "s", which is a function of thickness of the plate, the index of refraction of the shearing plate material, and the angle of incidence.
  • the value of the shear can be calculated directly from these parameters.
  • Fig. IB shows a plan view arrangement of a lateral shearing plate interferometer with a laser source 111 producing a beam 113 incident on an opti 114 under test.
  • Beam 113 exits the optic approximately collimated but slightly diverging, and is incident on a shearing plate 115.
  • the beam incident on the shearing plat is shown diverging to an exaggerated degree to facilitate illustration of virtual sources.
  • the outer edges of the incident beam reflect from the front surface of the shearin plate at points 117 and 119.
  • the outer edges of the incident beam reflect from the back surface at points 121 and 123.
  • the reflected beams partially superimposed, travel in the direction of arrow 125 away from the shearing plate, and appear to come from two different virtual sources, one at point 127 and the other a point 129.
  • These two virtual sources have a lateral separation, s, the lateral shear, and also an axial separation, 1, called the axial delay.
  • s lateral separation
  • Fig. 2 shows a theoretical superposition of the two reflected beams of Fig. 1A as they would look if they were incident on a plane surface 131 viewed in the direction of arrow 125.
  • the beam reflected from the front surface is represented by circle 133 on surface 131 in Fig. 2 and the beam reflected from the back surface is represented by circle 135.
  • the two beam circles are offset by the distanc of the lateral shear s.
  • Area 137 is the area of superposition and interference of the reflected beams. If the laser beam is reasonably free of aberrations and close to collimation, the interference area will show parallel alternating light and dark bands (fringes) , approximately a shown in Fig.
  • interferometer with the capability to measure the complex amplitude (both field amplitude and field phase) profile of a laser beam wavefront, and to convert the measurement into parameters which are commonly used to characterize lasers. These parameters include beam quality characteristics, such as M 2 and Strehl ratio, which describe how well the laser beam will focus, and other parameters related to optical aberrations, such as Zernicke polynomials and Seidel aberration coefficients.
  • the interferometer should also provide for straight-forward conventional measurement of aberrations of optical compoonents and systems. Summary of the Invention
  • a wavefront analyzing interferometer that can be used either to fully characterize (i.e., measur the complex field amplitude of) a laser wavefront or to tes optical components or systems, and that is robust enough to operate in a normal factory environment.
  • the instrument is a lateral wavefront shearing phase shift interferometer. I is inherently mechanically stable and relatively inexpensi because of its simplicity. It has readily adjustable sensitivity, so that it can directly measure even steep wavefronts which produce very high fringe densities that cannot be measured using the usual commercial interferometers.
  • the interferometer is made up a shearing element for amplitude division by reflection of an incident beam of electromagnetic radiation into two parts, each part having a wavefront with a direction of propagation that is substantially parallel to the other, t two parts being displaced relative to each other in a direction transverse to the direction of the incident beam so as to cause interference fringes between the two parts; and a mounting element for supporting the shearing element and for rotating the shearing element by small amounts abo an axis transverse to the incident beam.
  • the shearing element includes shearing plate with flat faces and is made of a transparen material.
  • the optical delay of the interferometer is changed by rotating the shearing plate of the interferomet through a small angle relative to the incident light beam means of the mounting element.
  • the mounting element includes a thermally driven wire that is self-calibrated by means of its resistance so as to rotate the shearing plate relative to a portion of the mounting element via thermal expansion of the wire.
  • the desired phase shift is provided by the amount of rotation of the shearing plate.
  • Fig. 1A is a plan view of a shearing plate arranged at an angle with a laser source, an optic under test and a display surface to illustrate the principles of lateral shearing interferometry.
  • Fig. IB is a cross-sectional view of the shearing plat of Fig. 1A showing the geometry of various rays of light traversing and reflecting from the shearing plate.
  • Fig. 2 is a view of an interference pattern produced b the arrangement of elements of Fig. 1.
  • Fig. 3 is an expanded view of a dynamic lateral shearing interferometer according to a preferred embodiment of the invention.
  • Fig. 4 is an assembled view of the interferometer of Fig. 3.
  • Fig. 5 shows a typical measurement setup for using the personal interferometer to characterize the wavefront of an optic under test.
  • Fig. 6 is a schematic of a drive system for rotating the shearing plate of the personal interferometer in a calibrated manner.
  • Fig. 7 is a schematic of an alternative drive system for rotating the shearing plate of the personal interferometer in a calibrated manner.
  • Fig. 8 is a schematic of a portion of an alternative embodiment of the invention designed to measure wavefront characteristics along two axes simultaneously.
  • Fig. 9 is a schematic of an interferometer system according to the invention for sequentially measuring wavefront characteristics along two axes. Description of the Preferred Embodiments
  • Interferometer 11 Illustrated in Fig. 3 is an expanded view of a dynamic lateral shearing interferometer 11 which can be used for studying wavefront profiles.
  • Interferometer 11 includes an uncoated, plane-parallel glass plate (i.e. shearing plate) , hereinafter etalon 13, mounted in a ring structure 15, typically constructed of black-anodized aluminum, although other materials could also be used.
  • shearing plate plane-parallel glass plate
  • etalon 13 mounted in a ring structure 15 typically constructed of black-anodized aluminum, although other materials could also be used.
  • the mounting ring is partially split into a front half 37, which houses etalon 13, and a back half 35 which is attached via a threaded mounting hole 18 to an adjustable mounting post 17, such as an industry standard stainless steel 1/2 inch (1.27 cm) post.
  • the mounting post is supported by a stable base assembly 19 that is a commercially available rotation stage. Due to the fact that the base assembly is a rotation stage, it includes angular gradations so that angular rotations of the interferometer relative to the base can be accurately measured.
  • the mounting ring has been partially split by cutting through the ring in the middle along a vertical axis, with cuts 28 and 29 terminating in two pairs of stress relief drill holes 20 and 21, and 22 and 23.
  • a saw cut of about 1/16 inch (0.16 cm) in width is preferred.
  • the uncut regions between the pairs of drill holes form an integral pair of flexure hinges 25 and 27 located along a vertical diameter of the etalon.
  • the flexure hinges permit a small amount of frictionless rotation of the etalon and its mounting ring relative to the base assembly. As will be discussed subsequently, this motion can be used to change the angle of incidence of an incident beam being tested, thereby causing an associated interferometer fringe pattern to be scanned.
  • the mounting ring is constructed of a piece of aluminum pipe, 3 inch (7.62 cm) schedule 80, 6061-T6 aluminum, having a length of about 1.375 inches ( 3.5 cm) . Nominally the pipe has a standard inner diameter of 2.9 inches (7.37 cm).
  • the pipe In order to accommodate a 3 inch diameter etalon that is 1/2 inch (1.27 cm) thick, the pipe is typically milled to provide an opening of 3.01 to 3.02 inches (7.65 to 7.67 cm) on one side that is slightly deeper than 1/2 inch (1.27 cm), 0.550 inches (1.40 cm) being preferred.
  • This also provides a land 30 for the etalon near the middle of the pipe. The etalon is mounted in front half 37, against land 30, and is held in place by two tabs 38 and 40 held by two screws 42 and 44.
  • the diameter of drill holes 20-23 is 3/8 inches (0.95 cm) with a center-to-center separation between adjacent pairs being about 0.438 inches (1.11 cm), leaving a separation between the edges of the holes of about 1/16 inches (0.16 cm) for the flexure hinges.
  • the etalon in the preferred embodiment is nominally a 3 inch diameter by 1/2 inch thick plate of BK-7 glass. Other materials, such as fused silica may also be used.
  • the etalon in the preferred embodiment has a flatness specification of less than or equal to Lambda/10 at 633 nanometers with a clear aperture of 3 inches. Also in the preferred mode, the residual wedge is specified at less tha Lambda/10 at 633 nanometers.
  • Fig. 5 Shown in Fig. 5 is a typical measurement setup for using the personal interferometer 11 to determine wavefront characteristics of an optic 311 under test.
  • the apparatus is set up so that a laser 309 provides a beam through optic 311 which is approximately collimated if the optic were free of aberrations.
  • the personal interferometer is positioned in the beam that emerges from the optic, and the interferometer stage is rotated such that the beam is retroreflected back to the source.
  • the rotation stage of the interferometer is then used to rotate the angle of incidence of the laser beam in order to provide a shear of the reflected beams of about 1/3 of a beam diameter.
  • the precise angle of incidence is read off from the stage and entered into a computer 315.
  • the user then enters the laser wavelength into the computer, which then determines the precise incremental etalon rotation needed to change the interference phase by 1/4 wave using the wavelength, the angle of incidence, and the thickness and index of refraction of the etalon.
  • the determination of the amount of etalon rotation that is required to change the phase by 1/4 wave can be made by precalibrating the instrument or by using algorithms to analytically perform such calculations. (The calibration approach is very simple and entails illuminating the interferometer with a collimated beam, rotating the etalon so that the interference pattern is changed by one fringe and is therefore identical to what it was before rotation, and dividing the rotation angle by 4.)
  • the user then initiates the measurement process.
  • a CCD camera 317 and a frame grabber 319 are used to capture one frame of video which is then stored in the computer.
  • the etalon is then rotated about the flexure hinges by the correct amount to provide a 1/4 fringe shift in the beam reflected from the etalon.
  • one frame of video is stored, and so forth until a total of four frames of video are stored.
  • the stored video data is processed using standard algorithms to provide the starting phase and the fringe contrast (depth of modulation) of the interferogram at each pixel in the frame.
  • the fringe pattern intensity distribution can be described by
  • A(x,y) is the complex field amplitude at point (x,y) and s is the shear, which is assumed to be along the x- direction.
  • the fringe phase, j- f (x,y) is shifted in steps of Pi/2, as described above, causing the measured intensity at each pixel to vary sinusoidally due to the last term in the equation.
  • a sequence of four measurements can be analyzed using the Fast Fourier Transform or other algorithms, to determine the amplitude and phase of the las term in the equation.
  • the fringe phase is processed using standard algorithm to generate the wavefront phase, j5(x . y) / at each pixel alon the shear (x) direction. That phase information is then converted into a wavefront profile map which is shown on display 321. Also, as is known in the art, other parameter can be calculated as well: for example, RMS error, peak- to-valley error etc.
  • A(x+s,y) j at each pixel is the product of magnitudes of the field amplitudes of the two sheared beams.
  • the fringe amplitude data along each ro of pixels is processed using standard algorithms, such as least squares fitting, to determine the field magnitude ⁇ A(x,y) j near the wavefront. This data, when combined with the wavefront phase at each pixel, (x,y) , gives the full complex field distribution
  • A(x,y)
  • ThermX translator includes a wire 31 (Fig. 4) that is connected under tension between front half 37 and back half 35 of ring structure 15.
  • An electrical circuit, hereinafter the ThermX translator driver, including control electronics that heats the wire is contained in package 49.
  • the wire is typically heated continuously to control its length, it is also continuously cooled by radiation and convection to its surrounding environment. (The ThermX translator and driver will be discussed in more detail subsequently.)
  • Wire 31 is connected to two threaded studs 41 and 43 (Fig. 4) , which are electrically insulated from the ring and which are connected to each of two power wires 45 and 47 that lead to the ThermX translator driver mounted in package 49 to the backside of the interferometer ring structure.
  • Driver Package 49 is separated from ring structure 15 on spacers such as spacer 51, and a thermal shield 53 is assembled between the ring and driver to prevent heat from the driver from affecting the thermal stability of the etalon.
  • the driver package could as well be mounted elsewhere, for example another preferred mode would be in the base, but the mounting shown in Fig. 4 has the advantage of allowing the power wires to be short.
  • the advantage of a base mounting for the driver package would be that it would permit transmission of the incident beam to occur which could be an advantage to use for high power lasers, and would also likely have less thermal excursions of the etalo due to heating from the circuit elements.
  • Nuts engage the threaded studs 41 and 43, and are used to apply initial tension on the flexure hinges, which in turn compress the front and back sides of the split ring structure toward each other, so that the gap of cut 28 is decreased.
  • the initial displacement is about 0.1 mm, which results in an initial angular displacement of the etalon of about 0.14 degrees.
  • wire 31 When wire 31 is heated or allowed to cool, it elongate or contracts ideally in proportion to its length and its thermal expansion coefficient. Hence, front half 37 which holds the etalon rotates about the flexure hinges relative to rear half 35 through a small angle, smaller than the initial displacement angle, as necessary to achieve a rotation of 1/4 fringe per frame.
  • the self-contained ThermX translator driver is powered by a DC power supply (not shown) .
  • the current supplied by the power supply controls the length of the wire and causes the etalon to be displaced through a small angle about the vertical axis defined by the flexure hinges of the ring structure. This small angle displacement changes the axial delay of the light reflected from the front and back surfaces of the etalon.
  • the system for changing the relative separation of the front half and the back half of ring structure 15 need not be the ThermX translator, but could be also be another kind of electromechanical system.
  • the ThermX translator is, however, a much simpler and more elegant implementation of a displacement system fo such moderately small displacements.
  • ThermX Translator and Drive As indicated earlier, the fundamental element of the ThermX drive system is resistive wire 31.
  • the wire is specially chosen to have both a large thermal expansion coefficient and a large temperature coefficient of resistance.
  • the wire is held under tension, and its length defines the spacing which is to be controlled.
  • the length of the wire at a temperature T(C) is
  • the resistance of the wire is given by
  • R R 0 (1 + a R *L/a L *L 0 - a R /a L ) and the change in resistance with length is given by dR - R 0 *a R . dL L 0 *a L
  • a current is passed through the wire to heat it and cause it to elongate, thereby increasing the controlled spacing.
  • the temperature of the wire and thus its length is monitored by sensing the resistance of the wire. Since the thermal expansion and the change of resistance are highly reproducible functions of temperature, the change in resistance of the wire provides an accurate measure of the change in length of the wire. Unlike most other transducers, the ThermX wire system provides both the drive mechanism and the position sensor in the same simple element.
  • Fig. 6 Shown in Fig. 6 is an electrical schematic of the ThermX drive.
  • the ThermX drive is a precision microtranslator that is particularly adapted for moving the etalon of the personal interferomete in very precise increments in order to carry out the calibrated phase shifts required for interferometric study of wavefront characteristics.
  • a Wheatstone bridge 205 is configured from resistors Rill, which is the ThermX drive resistance wire (31) , and resistors R211, R311, and R411. For best results these resistances are all approximately equal, about 2 Ohms.
  • the requirements for wire 31 were met using a resistance wire Stablohm 610, 36 AWG (0.005 inches diameter) , having a resistivity of 24 Ohms/linear foot, and a linear expansion coefficient of 15.6 parts/million/degree C.
  • This wire also has a thermal coefficient of resistance of 400 ppm/degree C.
  • the requirements for resistors R211, R311 and R411 were met using a resistance wire Stablohm 800, 36 AWG, having a resistivity of 32 ohms/linear foot, and a thermal coefficient of resistance of 5ppm/degree C.
  • These wires ca be obtained from California Fine Wire Company in Grover City, California. Other wires could also be used, of course, depending on the temperature characteristics desired.
  • Bridge 205 is used for sensing the resistance of Therm drive wire Rill, the resistance being directly proportional to the length of the wire to first order.
  • An AC signal fro a master oscillator 209 drives the bridge via an amplifier A4, while a DC current is provided from a computer controlled power supply 217 in order to adjust the length o wire Rill.
  • a capacitor Cl is used for DC isolation.
  • the bridge imbalance is detected by a differential amplifier A3 and a phase sensitive amplifier 213 amplifies the AC imbalance, the amplitude of which is proportional to the length of wire Rill.
  • the phase sensitive amplifier then feeds back a position signal to computer 215 which then adjusts the drive signal to power supply 217 to control the length of the wire accordingly.
  • the Wheatstone bridge balance is sensed using the DC current that heats the wire.
  • the error signal is normalized by dividing by the voltage across the bridge.
  • ThermX drive resistor is represented by Rl, typically about 2 Ohms.
  • R2 is the matching resistor for Rl, and is also typically about 2 Ohms.
  • the other side of the bridge is represented by resistors R3 and R4, which are typically much larger, for example both about IK Ohm.
  • Resistor R5 acts as a trim potentiometer, and in the this example has a resistance of about 100 Ohms.
  • A7 is an instrumentation amplifier, i.e.
  • DIV is a divider for normalizing the error signal.
  • an appropriate choice for divider DIV would be an AD633, also available from Analog Devices.
  • Al has a gain of about 1000, and DIV a gain of about 10, and the quiescent current through the bridge is about 0.2 A.
  • II is an integrator, which here is shown schematically as an operational amplifier, A8, with a capacitor C2, and a resistor R7.
  • V j ⁇ p is the driver for the VI node. (Ostensibly, without V ⁇ - p , VI and V2 would be equal, since VI would track V2, which is set by R5.)
  • V REF the drive current through the bridge can be changed such that the ThermX resistor Rl changes its resistance so as to change the voltage VI in a calibrated way (i.e. Rl tracks V REF ) • DIV serves to scale the signal from Amplifier A7 and provides the error signal for integrator II.
  • Fig. 8 shown schematically in Fig. 8 is a portion of an interferometer system which uses two shearing plates, 91 and 93, so that the wavefront shape can be measured along two orthogonal axes simultaneously.
  • the first plate 91 is oriented and rotated b its ThermX drive about one axis, say the vertical
  • the second plate is oriented and rotated by its ThermX drive about an orthogonal axis, shown schematically as horizontal axis 95.
  • Plate 93 then provides an interference pattern for the orthogonal axis which can also be detected just as before.
  • Another approach for measuring the wavefront shape along tw orthogonal axes is shown in Fig. 9.
  • th light incident from the optic under test is incident on an image rotator 1001, which then transmits the light to the interferometer.
  • image rotator 1001 With this system, one first determines th wavefront shape along one axis, then the image is rotated b 90 degrees by image rotator 1001, and the wavefront shape about an orthogonal axis is determined.
  • the phase shift method described above for determining fringe phase can also be used for a wedged shearing plate as well.
  • the above analysis can be applied to Fizeau interferometers, and as described in U.S. Patent 4,173,442 (incorporated herein by reference) , the laser wavelength can be determined from the fringe phase. Therefore, as an alternative embodiment, the interferometer according to the invention can be used to measure laser wavelength.
  • the size and material of the etalon can vary widely, the mechanical construction of the base and ring structures may change, and many dimensions can vary.
  • a power and control circuit may be designed to accomplish the purposes of the circuitry of the preferred embodiment for the ThermX drive.
  • An embodiment of the interferometer can also be provided within the spirit and scope of the invention wherein the shearing plate is pivoted to the support and a drive is provided to rotate the shearing plate.
  • a drive is provided to rotate the shearing plate.
  • the shearing plate may be pivoted in the support, and the drive can similarly take many forms to rotate the plate satisfactorily.
  • a workable drive could incorporate an electric motor and a driven cam engaging a follower on a housing for the shearing plate.

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  • Spectroscopy & Molecular Physics (AREA)
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  • Instruments For Measurement Of Length By Optical Means (AREA)

Abstract

L'interféromètre décrit par l'invention est constitué par un élément de coupure (13) servant à diviser l'amplitude, au moyen de la réflexion d'un faisceau incident de rayonnement électromagnétique en deux parties, chaque partie possédant un front d'ondes se propageant dans un sens sensiblement parallèle à l'autre, les deux parties se déplaçant l'une par rapport à l'autre dans un sens transversal à celui du faisceau incident, afin de provoquer des franges d'interférence entre les deux parties; par un élément de montage (15) servant à supporter l'élément de sectionnement (13) et à faire tourner ledit élément (13) sur des petites distances autour d'un axe transversal au faisceau incident. Dans le mode de réalisation préféré, l'élément de coupure (13) est constitué par une plaque de coupure en matériau transparent et pourvue de faces plates.
PCT/US1992/004025 1991-05-14 1992-05-13 Interferometre a coupure dynamique WO1992020991A1 (fr)

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US701,405 1991-05-14

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FR2732763A1 (fr) * 1995-04-06 1996-10-11 Zygo Corp Procede et systeme pour profiler une surface d'objet en utilisant une longueur d'onde equivalente importante
US6115126A (en) * 1998-02-05 2000-09-05 National Science Council Optical wavefront analyzer and method using a single wave shifter
WO2002012826A1 (fr) * 2000-08-04 2002-02-14 The Regents Of The University Of California Interferometre de cisaillement lateral double domaine
GB2431986A (en) * 2005-11-03 2007-05-09 Isis Innovation Detecting the local slope and orientation of a wavefront from the changes in an interference pattern caused by the rotation of a shearing element

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FR2732763A1 (fr) * 1995-04-06 1996-10-11 Zygo Corp Procede et systeme pour profiler une surface d'objet en utilisant une longueur d'onde equivalente importante
US6115126A (en) * 1998-02-05 2000-09-05 National Science Council Optical wavefront analyzer and method using a single wave shifter
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JPH06500405A (ja) 1994-01-13
EP0539571A1 (fr) 1993-05-05
EP0539571A4 (en) 1993-12-15

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