scispace - formally typeset
Search or ask a question

Showing papers on "Interferometry published in 1973"


Journal ArticleDOI
TL;DR: In this paper, a fringe system is obtained showing contours of constant slope resolved in the direction of image displacement, which is a comparison with result obtained by holographic interferometry.
Abstract: The surface to be studied is illuminated with laser light and two images are formed, displaced relative to one another in the image. Speckle pattern interferometry is used to measure phase changes between the two images resulting from deformation of the surface. A fringe system is obtained showing contours of constant slope resolved in the direction of image displacement. A comparison is made with result obtained by holographic interferometry.

298 citations


Journal ArticleDOI
TL;DR: An extension of the static technique to real- time dynamic testing is proposed and an operational variable-sensitivity interferometer utilizing the real-time technique is described.
Abstract: Previous methods of two-wavelength variable-sensitivity interferometry are reviewed and a simplified two-wavelength technique for interferometric testing under static conditions is discussed. An extension of the static technique to real-time dynamic testing is proposed and an operational variable-sensitivity interferometer utilizing the real-time technique is described.

240 citations


Book
01 Jan 1973
TL;DR: In this paper, a beam of light can be modeled as a wave of oscillating electric and magnetic fields, and two or more beams of light meet in space, these fields add according to the principle of superposition.
Abstract: Introduction A beam of light can be modeled as a wave of oscillating electric and magnetic fields. When two or more beams of light meet in space, these fields add according to the principle of superposition. That is, at each point in space, the electric and magnetic fields are determined as the vector sum of the fields of the separate beams. If each beam of light originates from a separate source, there is generally no fixed relationship between the electromagnetic oscillations in the beams. At any instant in time, there will be points in space where the fields add to produce maximum field strength. However, the oscillations of visible light are far faster than the human eye can apprehend. Since there is no fixed relationship between the oscillations, a point at which there is a maximum at one instant may have a minimum at the next instant. The human eye averages these results and perceives a uniform intensity of light. If two beams of light originate from the same source, there is generally some degree of correlation between the frequency and phase of the oscillations. At one point in space the light from the beams may be continually in phase. In this case, the combined field will always be a maximum and a bright spot will be seen. At another point the light from the beams may be continually out of phase and a minima, or dark spot, will be seen. Thomas Young was one of the first to design a method for producing such an interference pattern. He allowed a single, narrow beam of light to fall on two narrow, closely spaced slits. Opposite the slits he placed a viewing screen. Where the light from the two slits struck the screen, a regular pattern of dark and bright bands appeared. When first performed, Young’s experiment offered important evidence for the wave nature of light. In 1881, 78 years after Young introduced his two-slit experiment, A.A. Michelson designed and built and interferometer using a similar principle. Originally built to test for the existence of the ether, Michelson’s interferometer has become a widely used instrument for measuring the wavelength of light, for using the wavelength of a known light source to measure extremely small distances, and for investigating optical media.

206 citations


Journal ArticleDOI
TL;DR: In this article, numerical and analytical techniques are presented that allow three-dimensional, asymmetric, refractive index fields to be reconstructed from optical pathlength measurements, which can be obtained using multidirectional holographic interferometry.
Abstract: Numerical and analytical techniques are presented that allow three-dimensional, asymmetric, refractive index fields to be reconstructed from optical pathlength measurements, which can be obtained using multidirectional holographic interferometry. Analytical reconstruction techniques that have been used in radioaptronomy and electron microscopy for a number of years, and recently in interferometry, are presented in the context of interferometric applications in the refractionless limit. These techniques require that optical pathlength data be collected over a 180 degrees angle of view. The required pathlength sampling rate is discussed. An efficient numerical procedure is developed for direct inversion of the data. Several numerical techniques are developed that do not require that data be collected over a full 180 degrees angle of view. All such techniques require redundant data to achieve accurate reconstructions. The required degree of redundancy increases as the angle of view decreases. Numerical simulations using six different reconstruction techniques indicate that with a 180 degrees angle of view, all are capable of providing accurate reconstructions. Four of the techniques were used to analyze simulated interferometric data recorded over an angle of view of less than 180 degrees . Examples of reasonably accurate reconstructions using data with angles of view as low as 45 degrees are presented.

177 citations


Journal ArticleDOI
TL;DR: A simple grating lateral shear interferometer is described that can be made to give simultaneously two interferograms having shear in two orthogonal directions to be used with real-time heterodyne phase detection.
Abstract: A simple grating lateral shear interferometer is described that can be made to give simultaneously two interferograms having shear in two orthogonal directions. The shear for the two orthogonal directions is produced in one plane by one double frequency crossed diffraction grating that can easily be produced holographically. Translating the grating sideways causes the irradiance of the interferogram to vary sinusoidally with time enabling the interferometer to be used with real-time heterodyne phase detection.

150 citations


Journal ArticleDOI
TL;DR: In this article, the theoretical wave nature of the electromagnetic fields about various types of dipole sources placed on the surface of a low-loss dielectric half-space and two-layer earth was examined.
Abstract: Radio interferometry is a technique for measuring in‐situ electrical properties and for detecting subsurface changes in electrical properties of geologic regions with very low electrical conductivity. Ice‐covered terrestrial regions and the lunar surface are typical environments where this method can be applied. The field strengths about a transmitting antenna placed on the surface of such an environment exhibit interference maxima and minima which are characteristic of the subsurface electrical properties. This paper (Part I) examines the theoretical wave nature of the electromagnetic fields about various types of dipole sources placed on the surface of a low‐loss dielectric half‐space and two‐layer earth. Approximate expressions for the fields have been found using both normal mode analysis and the saddle‐point method of integration. The solutions yield a number of important results for the radio interferometry depth‐sounding method. The half‐space solutions show that the interface modifies the directio...

127 citations


Journal ArticleDOI
TL;DR: In this article, a dual frequency method interpolates the fringe pattern of any kind of hologram interfermetry down to better than 1 100 of a fringe, independent of intensity variations.

96 citations


Journal ArticleDOI
01 Jan 1973
TL;DR: The NRAO Mark II interferometer as discussed by the authors is a television-type rotating-head video recorder with one-bit sampled data at a 4-Mb rate, which is used for connecting existing radio-telescope systems into interferometers, with baselines ranging from a few kilometers to nearly the diameter of the earth.
Abstract: Several tape-recorder interferometer systems have been constructed in the last few years. These systems are used for connecting existing radio-telescope systems into interferometers, with baselines ranging from a few kilometers to nearly the diameter of the earth. The NRAO Mark II interferometer system is in wide use. This, and the fact that its properties are typical of those of such systems in general, justifies a detailed description of the system. The system is based on a television-type rotating-head video recorder. One-bit sampled data are recorded at a 4-Mb rate. After recovery, the data are processed in special-purpese digital devices and general-purpose digital computers to complete the interferometer system. For purpose of this description, the software is regarded as an intrinsic part of the system.

66 citations


Journal ArticleDOI
TL;DR: A method of stabilizing a Fabry-Perot interferometer with respect to a reference wavelength, while simultaneously stabilizing the parallelism of the flats, is described and allows simultaneous stabilization and data taking, since the instrument is continuously updating itself.
Abstract: A method of stabilizing a Fabry-Perot interferometer with respect to a reference wavelength, while simultaneously stabilizing the parallelism of the flats, is described. The method consists of creating correcting signals proportional to the displacement of the fringe maxima of three auxiliary spectral sources with respect to a fixed reference point and feeding these signals back to the interferometer piezoelectric drive so that the correcting signals become time invariant, and the interferometer is stabilized. The stability of the finished instrument with respect to the reference wavelength and parallelism is near lambda/1000, at 546 nm, for a 6-h period; however, the actual parallelism of the etalon is limited by the surface defects of the flats. The method, as described, allows simultaneous stabilization and data taking, since the instrument is continuously updating itself.

61 citations


Book
15 May 1973
TL;DR: In this paper, the authors developed the theory of diffraction based on scalar theory, and approached information processing and holography by means of the elementary point concept and linear system theory.
Abstract: The field of coherent optics has stimulated much interest and indeed excitement over the past decade, and a number of engineering applications have been brought to light. The most significant of these are the subject of this senior- or graduate-level text, which was originally prepared--but is not limited to--electrical engineering students. It emphasizes the analogy between optical and electrical systems, both of which, for example, are capable of performing Fourier transform operations and signal filtering and processing.The book is designed for students without an intensive background in electromagnetic theory and classical optics. Its discussion of diffraction is based on scalar theory, and it approaches information processing and holography by means of the elementary point concept and linear system theory. This approach simplified the analysis so that solutions may be directly calculated, and it will appeal to engineering students because of their familiarity with the concepts of the impulse response of linear systems.After an opening presentation of the basic properties of linear systems and Fourier transformations, the book develops the theory of diffraction. The topics taken up include, among others, Fraunhofer and Fresnel diffraction, the reciprocity theorem, Huygens' principle, Kirchhoff's integral, the Fresnel zone plate, the Rayleigh criterion, and Abbe's sine condition. This part closes with a discussion of coherent theory and the mutual coherence function.The next part, on information processing, covers the Fourier transform properties of lenses and linear optical imaging systems, filtering, the basic properties of photographic film as a recording medium, film-grain noise and signal-to-noise ratio, the information channel capacity of photographic film, and optical resolving power and its relation to the uncertainty of information and physical realizability.The final part throws a clear light on the subject of holography. The presentation includes both linear and nonlinear holograms and takes up wavefront construction and reconstruction, magnifications, resolution limits and bandwidth requirements, finite-point analysis linear optimization techniques, syntheses of optimum nonlinear spatial filters, and applications. Among the latter are microscopic wavefront reconstruction, multiexposure holographic interferometry, time-average interferometry, and contour generation.

60 citations


Journal ArticleDOI
TL;DR: In this article, the use of diffraction gratings as beamsplitters in an oblique incidence interferometer and the application of that interferometers to measuring the flatness of non-optical surfaces was demonstrated.
Abstract: This paper demonstrates the use of transmitting diffraction gratings as beamsplitters in an oblique incidence interferometer and the application of that interferometer to measuring the flatness of non-optical surfaces. Many different surfaces have been examined, ranging from lapped granite and steel to unworked metal and processed photographic emulsions. The fringe interval in the interferograms is independent of the illuminating wavelength, being one half of the diffraction grating periodicity, which in the interferometer described is 5 mu m. It is also demonstrated that the topography of large surface areas may be evaluated by the combinations of interferograms.

Journal ArticleDOI
TL;DR: In this article, the authors suggest that a recent method of stellar interferometry developed by Labeyrie and his colleagues may be used to obtain diffraction-limited resolution from telescopes whose aberrations are poor by conventional standards.

Journal ArticleDOI
01 Sep 1973
TL;DR: In this paper, the authors discuss the coherence and timing requirements and calibration procedures for long-baseline interferometry, and some pertinent phenomena connected with radio-wave scattering in irregular media are discussed.
Abstract: Long-baseline interferometry achieves high resolution by using two or more widely separated radio telescopes and recording video signals on magnetic tapes, which are later brought together and cross-correlated. This paper contains discussions of the coherence and timing requirements and of calibration procedures. Applications to measuring brightness distributions and to spectroscopy are reviewed briefly. Some pertinent phenomena connected with radio-wave scattering in irregular media are discussed.

Journal ArticleDOI
TL;DR: In this paper, a simple theory of the superconducting single junction interferometer (ac Squid) becomes possible if the critical current of the single junction is small relative to Φ 0/LR.
Abstract: A simple theory of the superconducting single‐junction interferometer (ac Squid) becomes possible if the critical current of the single junction is small relative to Φ0/LR, where Φ0=h/2e is one flux quantum and LR is the inductance of the interferometer loop This theory predicts a magnetic flux sensitivity which has the same dependence on interferometer parameters as the existing theories for higher critical currents In contrast to those theories, however, the present theory predicts that the maximum flux sensitivity will be achieved off resonance Theoretical predictions for comparison with experiment are displayed as a function of the normalized difference between the operating frequency ω and the resonant frequency ω0

Journal ArticleDOI
TL;DR: In this article, an improved cube-corner shearing interferometer for measuring the MTF of atmospheric propagation paths and for making coherence measurements is described, and the laboratory unit used in all the experiments described was operated satisfactorily on board a KC-135 jet aircraft.
Abstract: An improved cube-corner shearing interferometer for measuring the MTF of atmospheric propagation paths and for making coherence measurements is described. The laboratory unit used in all the experiments described was operated satisfactorily on board a KC-135 jet aircraft. MTF data over a 13.3-km horizontal path near the ground, and through the atmosphere using star sources, have been compared with the MTF curves estimated by use of the Fried theory and published models for the atmospheric structure constant CN. The MTF has been measured with laser sources between the wing tip and the skin of the KC-135 in flight, and through the boundary layer within 25 cm of the skin in daylight and at night. The main degradation to the seeing was found to be in the boundary layer within 25 cm of the skin outside the aircraft window.

Journal ArticleDOI
Olof Bryngdahl1
TL;DR: In this paper, the radial and circular-fringe interferograms have been proposed to transform the reference wave in a conventional interferometer so that a new type of interferogram is obtained.
Abstract: New types of interference-fringe configurations in displays of interferograms are introduced. In particular, two types that show the data directly in polar coordinates appear attractive. These are radial-and circular-fringe interferograms. Several ways are described to transform the reference wave in a conventional interferometer so that a new type of interferogram is obtained. Feasibility experiments have been promising. Spiral-fringe interferograms have also been realized.

Journal ArticleDOI
TL;DR: In this paper, light scattered from oppositely directed surface acoustic waves on ycut zpropagating lithium niobate was frequency analyzed with a high-resolution Fabry-Perot interferometer.
Abstract: Under conditions of continuous acoustic generation, light scattered from oppositely directed surface acoustic waves on y‐cut z‐propagating lithium niobate was frequency analyzed with a high‐resolution Fabry‐Perot interferometer. The following parameters were measured at 105 MHz: acoustic power standing‐wave ratio, reflection coefficient for both sending and receiving transducers, low‐power acoustic damping coefficients, surface wave propagation velocity, and nonlinear harmonic growth. We note that the method used has an advantage over other methods since it is to a large extent independent of the optical quality of the propagation surface.

Journal ArticleDOI
01 Sep 1973
TL;DR: In this paper, the authors present a review of the techniques used for earth-rotation aperture synthesis, including the response of a two-element interferometer and the geometry associated with earth rotation synthesis.
Abstract: Resolution for radio astronomy in the order of 1" is necessary for the study of distant radio galaxies and quasars, for detecting faint sources, and for the mapping of clouds of hydrogen and other molecules. To obtain these resolutions many new or planned radio instruments use arrays of moderate size radio telescopes to synthesize large physical apertures. These instruments are generally composed of one or several linear arrays and utilize the rotation of the earth to change the relative orientation of the array and the radio source. The techniques used for earth-rotation aperture synthesis are discussed. The response of a two-element interferometer and the geometry associated with earth-rotation synthesis are reviewed; the current and proposed designs for these instruments and their performance are described; and, finally, the inversion methods for determining the angular power distribution of a radio source from the array response (visibility function) are outlined.

Journal ArticleDOI
TL;DR: In this paper, the choice of the plane of focus and the alignment of the object with respect to the light direction have been found to affect the distortions of refractive-index fields.
Abstract: Distortions in interferograms of refractive-index fields due to deviations from straight-line propagation have been analyzed numerically. Quantitative refractive-index profiles can often not be derived in a simple way from interferograms. The choice of the plane of focus and the alignment of the object with respect to the light direction are found to affect the distortions greatly. Results for typical examples of refractive-index fields encountered in different electrochemical systems are given.

Journal ArticleDOI
TL;DR: Two simultaneous holograms and several directions of observation are utilized to determine the components of displacement and strain in the disk.
Abstract: Two simultaneous holograms and several directions of observation are utilized to determine the components of displacement and strain in the disk. A reference strip is introduced to relate the fringe orders in the two holograms. A very good agreement is obtained between the holographic results and the elasticity theory solution. The obtained displacement field is estimated to be accurate to 8 x 10(-6) cm, which is approximately one-eighth the wavelength of the laser light utilized to obtain the holograms.

Patent
S Ramsey1
13 Apr 1973
TL;DR: In this article, a real-time holographic interferometer for measuring deformation of objects is presented, where four independent holographic interference patterns are formed with on-axis object and reference beams.
Abstract: A real time holographic interferometer for measuring deformation of objects Four independent holographic interference patterns are formed with on-axis object and reference beams The first two interference patterns are of the object in a first physical state, eg, in its first state of stress, or of a reference plane, and the second two interference patterns are of the object in a second physical state, eg, in its second state of stress The phase of the reference beam is shifted 90* for each exposure A storage-type television camera is employed for generating output signals that contain information from the four interference patterns The first three output signals of the camera are stored in video recorders and are retrieved synchronously with the fourth camera output signals Two signal pairs each consisting of a signal of the first and second states of stress of the object are combined and subtracted to form difference signals which are thereafter electronically squared and summed to generate a processed signal that contains the desired deformation information The processed signal is utilized such as for driving a cathode ray tube

Journal ArticleDOI
Eric G. Rawson1, R. Murray
TL;DR: A simple and sensitive interferometric technique which yields accurate measurements of the 2nd-, 4th-, and 6th-order coefficients of the series expansion for the radial distribution of the dielectric constant of SELFOC or other GRIN rods is reported in this paper.
Abstract: A simple and sensitive interferometric technique which yields accurate measurements of the 2nd- , 4th-, and 6th-order coefficients of the series expansion for the radial distribution of the dielectric constant of SELFOC or other GRIN rods is reported. Such data are required, for example, in predicting temporal dispersion in SELFOC fiber waveguides. The interferometer directly measures the relative phase delay along meridional-ray paths of different initial field angles. The mathematical analysis consists of finding the 2nd-, 4th-, and 6th-order coefficients which yield the best least squares fit to the measured phase shifts. The 4th-order results are found to be in good agreement with those of I. Kitano and co-workers. As an experimental application we describe a small, mechanically stable, diffraction-limited collimator for use with an optical fiber waveguide.

Patent
C Velzel1
06 Apr 1973
TL;DR: In this article, the phase difference is produced between two sub-beams polarized in directions at right angles to one another by means of an electro-optical modulator, the displacement being effected in an interferometer which discriminates in respect of direction of polarisation.
Abstract: An apparatus for measuring the roughness of a surface is described which includes an optical system by means of which two images of the surface which have a mutual phase difference and displacement are superposed on one another. It is disserted that for this purpose the phase difference is produced between two sub-beams polarized in directions at right angles to one another by means of an electro-optical modulator, the displacement being effected in an interferometer which discriminates in respect of direction of polarisation. It is set forth that the interferometer may include the series arrangement of the two Wollaston prisms which produce opposite angle splittings between cross-polarized beams of radiation which enter the series arrangement.

Journal ArticleDOI
TL;DR: A lens-testing system using a simple wavefront shearing interferometer, which is inexpensive, portable, relatively insensitive to vibration, does not need laser illumination, and requires only a minimum of experimental time and operational expertise.
Abstract: A lens-testing system using a simple wavefront shearing interferometer is described. This simple cube interferometer has all the interferometric adjustments built in at manufacture. In contrast to most interferometric test systems, the wavefront shearing interferometer is inexpensive, portable, relatively insensitive to vibration, does not need laser illumination, and requires only a minimum of experimental time and operational expertise. Reading of the interferograms and subsequent data reduction require the major effort in testing with the wavefront shearing interferometer. However, with automatic scanning of the interferograms and a high-speed electronic computer to perform the analysis, the data reduction may be completely automated. Operation of the wavefront shearing interferometer is described together with the method of data reduction. Experimental results are also presented.

Journal ArticleDOI
TL;DR: In this paper, a Fabry-Perot interferometer was used in the cavity cavity of a mode-locked Nd-glass laser to reduce the spectral narrowing effect.

Journal ArticleDOI
TL;DR: In this article, a pulsed ruby laser is used as the light source so that highfrequency turbulence in the flow can be instantaneously recorded, and hence, frozen in time, and the unique feature of dual hologram interferometry is that the no flow and flow conditions are recorded at different times on separate holograms.
Abstract: T study shows that dual hologram interferometry can be used to accurately measure local densities in wind-tunnel experiments, and that this technique does not suffer from some of the serious limitations of previous interferometric methods. A pulsed ruby laser is used as the light source so that highfrequency turbulence in the flow can be instantaneously recorded, and hence, frozen in time. The unique feature of dual hologram interferometry is that the no flow and flow conditions are recorded at different times on separate holograms. Because of this, movement between exposures is not recorded in the interferogram, and therefore, the method is not sensitive to wind-tunnel vibration. The images are interfered upon reconstruction, and the fringe configuration is controlled by precisely varying the orientation of the two holograms with respect to each other. ~ The heart of a practical, operational system is the dual hologram plate holder which is used to hold and precisely align the two holograms during image reconstruction. To demonstrate the accuracy and versatility of this method, three separate Mach 3 flowfields were considered in the original paper, but only the flat plate turbulent boundary-layer results are presented here.

Journal ArticleDOI
TL;DR: A stable, piezoelectric scanning Fabry-Perot interferometer is used in conjunction with a conventional grating monochromator to obtain an over-all spectral bandwidth of 0.013 A with moderate light gathering power.
Abstract: A stable, piezoelectric scanning Fabry-Perot interferometer is used in conjunction with a conventional grating monochromator to obtain an over-all spectral bandwidth of 0.013 A with moderate light-gathering power. A multilayer dielectric reflective coating is used for atomic absorption measurements with a continuum source in the 3200 to 3600 A region. Results for Cu and Ag show that sensitivities obtained are the same as those obtained with line sources. Profiles of the 3247 A copper and 3383 A silver resonance lines were obtained, and the half-widths reported.

Patent
07 Sep 1973
TL;DR: In this paper, a control system for positioning a movable table relative to a tool head with high accuracy employs laser interferometers for position feedback, which can be mounted on a stationary tool head and cooperate with retroreflectors mounted on the table to measure the displacements of the table relative with the head along two orthogonal measuring axes.
Abstract: A control system for positioning a movable table relative to a tool head with high accuracy employs laser interferometers for position feedback. Interferometers are mounted on a stationary tool head and cooperate with retroreflectors mounted on the table to measure the displacements of the table relative to the head along two orthogonal measuring axes. Strategic positioning of the interferometers causes the measuring axes to intersect the tool head axis and thereby eliminates certain measurement errors inherent in other systems.

Journal ArticleDOI
TL;DR: In this article, the authors used two coherent light beams focused on the specimen surface to directly record standing-wave ratio, attenuation, transmission, harmonic content, and other characteristics of surface waves at frequencies ranging from audio to beyond 200 MHz.
Abstract: The use of optical interferometry for measurement of ultrasonic surface waves has been limited heretofore by the necessity of maintaining the surface under test within a fraction of a wavelength of light of some fixed position. A new technique, using two coherent light beams focused on the specimen surface, avoids this limitation. This technique is useful for directly recording standing‐wave ratio, attenuation, transmission, harmonic content, and other characteristics of surface waves at frequencies ranging from audio to beyond 200 MHz. In addition to excellent sensitivity, the method allows absolute calibration of the acoustic wave amplitude.

Journal ArticleDOI
TL;DR: In this paper, a laser Doppler interferometric technique for measuring small absorption coefficients of infrared-transmitting materials is described, where the interferometer is calibrated as a remote temperature sensor by monitoring optical path length changes of the sample as a function of temperature.
Abstract: A laser Doppler interferometric technique for measuring small absorption coefficients of infrared‐transmitting materials is described. The interferometer is calibrated as a remote temperature sensor by monitoring optical path length changes of the sample as a function of temperature. The sample is then irradiated by a CO2 laser and the change in optical path due to absorbed laser energy is observed interferometrically as a function of time. From this measurement and the calibration data, a temperature‐vs‐time curve is generated from which the absorption coefficient of the sample at 10.6 μ may be calculated.