Showing papers on "Interferometry published in 1972"
TL;DR: In this article, a laser velocity interferometer instrumentation system was developed which can measure the velocity history of either spectrally or diffusely reflecting surfaces, and achieved accuracies of 2% or better for peak surface velocities of 0.2 mm/μsec.
Abstract: A laser velocity interferometer instrumentation system has been developed which can measure the velocity history of either spectrally or diffusely reflecting surfaces. The system provides two interferometer fringe signals in quadrature to improve resolution and to distinguish between acceleration and deceleration. Accuracies of 2% or better are attainable for peak surface velocities of 0.2 mm/μsec or more. The system has been applied to the measurement of free surface motion in plate‐impact experiments, and to the measurement of the velocity history of a projectile during its acceleration down a long gun barrel.
1,607 citations
TL;DR: A method for determining particle size, number density, and velocity utilizing a laser interferometer is analyzed and shows that when the fringe spacing is comparable to a particle diameter, size can be estimated and number density can be measured.
Abstract: A method for determining particle size, number density, and velocity utilizing a laser interferometer is analyzed. The results show that when the fringe spacing is comparable to a particle diameter, size can be estimated; and when the fringe spacing is much greater than the average particle diameter, number density can be measured. Since the optical arrangment for the interferometer is identical to that for a number of laser velocimeters, the effects of particle size on the velocimeter signal are discussed.
252 citations
TL;DR: In this article, the authors measured the frequency and wavelength of the methane-stabilized laser at 3.39 µm with infrared frequency synthesis techniques and obtained the following values: 88.376181627(50)$ THz.
Abstract: The frequency and wavelength of the methane-stabilized laser at 3.39 \ensuremath{\mu}m were directly measured against the respective primary standards. With infrared frequency synthesis techniques, we obtain $\ensuremath{
u}=88.376181627(50)$ THz. With frequency-controlled interferometry, we find $\ensuremath{\lambda}=3.392231376(12)$ \ensuremath{\mu}m. Multiplication yields the speed of light $c=299792456.2(1.1)$ m/sec, in agreement with and 100 times less uncertain than the previously accepted value. The main limitation is asymmetry in the krypton 6057-\AA{} line defining the meter.
194 citations
TL;DR: A system for extracting the phase components of an optical traveling wave field has been constructed using the Mach-Zehnder interferometer to capture the wave field as the hologram, a photoelectronic scanning system, and an analog computing circuit.
Abstract: A system for extracting the phase components of an optical traveling wave field has been constructed. This system consists of the Mach-Zehnder interferometer to capture the wave field as the hologram, a photoelectronic scanning system, and an analog computing circuit. The detected phase signal is immediately displayed on a cathode ray tube as continuous-tone patterns. The method has been confirmed through the experimental results.
151 citations
132 citations
TL;DR: The theory and experimental evidence of a shearing interferometer based on the Talbot effect, which can be reduced to triple-shearing or doubleshearing interferences by the addition of simple spatial filtering, is presented.
Abstract: The theory and experimental evidence of a shearing interferometer based on the Talbot effect are presented. Multiple-shearing interferences are obtained that can be reduced to triple-shearing or doubleshearing interferences by the addition of simple spatial filtering. When the shear is less than the width of the details in the object, these interferences become either the second or first derivative of the object under test, respectively. Either lateral or constant radial shear can be introduced by choosing Ronchi rulings or circular gratings. Thus both lateral and radial derivatives are easily obtained. If white light is used as a source, color fringes of high contrast are observed.
124 citations
TL;DR: An optical radar has been used to measure the radial wind velocity component in the lower troposphere by detecting interferometrically the bulk Doppler shift affecting the echoes from atmospheric aerosols as discussed by the authors.
Abstract: An optical radar has been used to measure the radial wind velocity component in the lower troposphere by detecting interferometrically the bulk Doppler shift affecting the echoes from atmospheric aerosols. The measurements, carried out at night, have basically utilized a highly coherent single-frequency Ar+ laser in the transmitter, and a small telescope, a scanning spherical Fabry-Perot interferometer, and a photon counting system in the receiver.
87 citations
TL;DR: In this article, the linear gratings in the Talbot interferometer are replaced by circular gratings, which are sensitive to the radial gradient of the object, and a new radial shearing interferometry is proposed.
72 citations
TL;DR: In this article, a He-Ne laser beam is sent through a common path differential interferometer and the interference signal is detected by a p-i-n photodiode.
Abstract: A He-Ne laser beam is sent through a common path differential interferometer and the interference signal is detected by a p-i-n photodiode. Weak phase objects can be examined because optical path changes can be resolved to 0.1 A with a time resolution of about 20 ns. Examples for different gas-dynamic investigations show good results and demonstrate the wide field of application for this type of laser interferometer.
72 citations
TL;DR: With the help of a simple ground glass and a photographic plate the phase variations of a transparent object can be studied.
Abstract: With the help of a simple ground glass and a photographic plate the phase variations of a transparent object can be studied. The object is interposed between the source and the ground glass. The photographic plate, kept behind the ground glass, is exposed successively twice, with and without the object. When properly illuminated the negative gives the variation in the derivative of the phase of the object, and this observation can be made in white light.
54 citations
TL;DR: Very-long-baseline interferometry experiments, involving observations of extragalactic radio sources, were performed in 1969 to determine the vector separations between antenna sites in Massachusetts and West Virginia, and found the 845.130-kilometer baseline was estimated from two separate experiments.
Abstract: Very-long-baseline interferometry experiments, involving observations of extragalactic radio sources, were performed in 1969 to determine the vector separations between antenna sites in Massachusetts and West Virginia. The 845.130-kilometer baseline was estimated from two separate experiments. The results agreed with each other to within 2 meters in all three components and with a special geodetic survey to within 2 meters in length; the differences in baseline direction as determined by the survey and by interferometry corresponded to discrepancies of about 5 meters. The experiments also yielded positions for nine extragalactic radio sources and allowed the hydrogen maser clocks at the two sites to be synchronized.
TL;DR: Intercomparison of radio signals received simultaneously at several sites from several sources with small mutual angular separation provides a powerful astrometric tool for determining the moon's libration, measuring winds in Venus's lower atmosphere, mapping Mars radiometrically, and locating the planetary system in an inertial frame.
Abstract: Intercomparison of radio signals received simultaneously at several sites from several sources with small mutual angular separation provides a powerful astrometric tool. Applications include tracking the Lunar Rover relative to the Lunar Module, determining the moon's libration, measuring winds in Venus's lower atmosphere, mapping Mars radiometrically, and locating the planetary system in an inertial frame.
Patent•
08 May 1972TL;DR: An interferometer system for measuring straightness including a light source for producing a beam of light, preferably a two frequency laser with the two frequency components linearly polarized and orthogonal to one another, the light beam being directed through a Wollaston prism where the beam is split into two separate paths which deviate in opposite paths from the original beam direction by a small angle as discussed by the authors.
Abstract: An interferometer system for measuring straightness including a light source for producing a beam of light, preferably a two frequency laser with the two frequency components linearly polarized and orthogonal to one another, the light beam being directed through a Wollaston prism where the beam is split into two separate paths which deviate, in opposite paths, from the original beam direction by a small angle. The two separate beams are transmitted over two separate paths to associated ones of two separate reflective surfaces which are mounted in a mutually fixed relationship and at an angle to each other. The two beams are reflected back into the prism from the associated reflective surfaces where they are recombined. Photodetector means are provided for detecting any changes in the fringes resulting from a change in one optical path length relative to other optical path length as the two mirrors move relative to the prism, said change in path lengths resulting from deviations from straightness in such movement. A dual system is disclosed for measuring rotational motion, i.e., roll.
TL;DR: The Mariner interferometer deviates in design from the Nimbus 3 and 4 interferometers in several areas, notably, by a cesium iodide beam splitter and certain aspects of the digital information processing.
Abstract: The Michelson interferometer on Mariner 9 measures the thermal emission spectrum of Mars between 200 and 2000 per cm (between 5 and 50 microns) with a spectral resolution of 2.4 per cm in the apodized mode. A noise equivalent radiance of 0.5 x 10 to the minus 7th W/sq cm/ster/cm is deduced from data recorded in orbit around Mars. The Mariner interferometer deviates in design from the Nimbus 3 and 4 interferometers in several areas, notably, by a cesium iodide beam splitter and certain aspects of the digital information processing. Special attention has been given to the problem of external vibration. The instrument performance is demonstrated by calibration data and samples of Mars spectra.
TL;DR: Measurements have been made with this technique of an area including the craters Ptolemaeus, Alphonsus, and Arzachel and a portion of Mare Nubium and there is evidence for a late episode of volcanism that partially filled two of the crater through a crustal fault of Imbrian origin.
Abstract: Radar interferometry is a new technique for accurately measuring the topography of the lunar surface from the earth. Measurements have been made with this technique of an area including the craters Ptolemaeus, Alphonsus, and Arzachel and a portion of Mare Nubium. There is evidence for a late episode of volcanism that partially filled two of the craters through a crustal fault of Imbrian origin. Several other features of the topography, particularly those coinciding with local gravitational anomalies, can be correlated with flow events.
Patent•
06 Jul 1972TL;DR: In this article, an interferometry of the matter waves accompanying particles such as neutral atoms, charged ions or electrons is described, and the resulting interference fringes can be measured by a suitable particle detector.
Abstract: An apparatus is disclosed which makes use of interferometry of the matter waves accompanying particles such as neutral atoms, charged ions or electrons. The apparatus includes a particle source and a beam splitter for splitting the original beam of particles into two beams having accompanying matter waves which are coherent with each other. The two beams are recombined by a pair of beam reflectors, and the resulting interference fringes may be measured by a suitable particle detector. Such an apparatus may be used for measuring variation of the gravitational field or the rate of rotation of the apparatus. In both cases the apparatus is capable of ultra precise measurement of acceleration, of the mass of an object or the rate of rotation. Alternatively, by utilizing charged particles it is possible to measure a magnetic field to obtain a magnetometer of great sensitivity. The apparatus may finally be used to carry out holography by matter waves.
TL;DR: A standard single pass schlieren system was converted into a single beamschlieren interferometer by replacing the knife edge with a polarizer-Wollaston prism-analyzer combination, and the results were shown to compare well with theoretical predictions.
Abstract: A standard single pass schlieren system was converted into a single beam schlieren interferometer by replacing the knife edge with a polarizer–Wollaston prism–analyzer combination. The system is described and an analysis given that relates the fringe shifts on the interferogram to density changes in the test section. The proper location of the density difference is discussed. A complex gas dynamic flow field was investigated with this interferometer, and the results were shown to compare well with theoretical predictions.
TL;DR: Single longitudinal mode operation of an optical parametric oscillator has been achieved using a low loss, mode-matched interferometer as a mode selector to obtain bandwidths of 0.001 cm-1 in the region of 2.5 μm.
TL;DR: In this article, the use of polarimetry and interferometry to study the optical properties of nematic liquid crystal films is discussed and theoretical formulation of the amplitudes, intensities and phase shifts of monochromatic light reflected or transmitted from multilayer films and experimental methods of determining the refractive indices and orientation order parameters of NLCs are presented.
TL;DR: This review describes how the interference properties of light have been applied to optical testing and indicates the main fields of application of the various techniques.
Abstract: The tolerances on optical systems and components are usually very tight and the testing of such products is a vital part of their manufacture. This review describes how the interference properties of light have been applied to optical testing and indicates the main fields of application of the various techniques.
TL;DR: Holograms are produced on bismuth and paraffin films with pulsed TEA CO2 laser light and the sensitivity of both films is about 0.3 J/cm2.
Abstract: Holograms are produced on bismuth and paraffin films with pulsed TEA CO2 laser light. Sensitivity of both films is about 0.3 J/cm2. Local resolution proved to be much better than 70 lines/mm. Capability of this holographic technique for interferometric measurements is demonstrated.
TL;DR: In this paper, the natural linewidths and line shapes due to quantum phase and quantum amplitude noise have been investigated within and below the threshold region of laser operation using a Fourier spectroscopic technique.
Abstract: The natural linewidths and line shapes due to quantum phase and quantum amplitude noise have been investigated above, within and below the threshold region of laser operation using a Fourier spectroscopic technique. Outside the threshold region the linewidths of the laser spectrum were found to be inversely proportional to the laser power, and measurements confirm the “factor of two” difference in the linewidth equation. Within the threshold region the results are in agreement with calculations of Hempstead, Lax and Risken. A Mach-Zehnder interferometer with optical path differences up to 1500 meters was used for the measurements. The method of investigation combines a high spectral resolution with a good signal-to-noise ratio. The method is suited to linewidth measurements of a laser both above and below threshold and allows the technical and natural linewidths to be clearly distinguished.
TL;DR: X-ray interferometer moire patterns have been used to completely determine the Burgers vectors of several dislocations as mentioned in this paper, and they have been obtained under controlled conditions and with many different Bragg reflections.
Abstract: X-ray interferometer moire patterns have been used to completely determine the Burgers vectors of several dislocations. Because x-ray moire patterns could be obtained under controlled conditions and with many different Bragg reflections it was possible to determine not only the magnitude direction and sense of the Burgers vectors but also to elucidate some hitherto unnoticed geometrical problems involved in the interpretation of x-ray interferometer moire patterns.
Patent•
24 Jan 1972
TL;DR: A phase interferometer elevation angle measurement radar has its antennas tilted slightly relative to each other so as to detect differences in amplitude from ground return signals; the phase difference in signals are checked for a positive rate of change; it is then compared against amplitude differences and is accepted as valid for use in generating an elevation angle only if within prescribed limits thereof as mentioned in this paper.
Abstract: A phase interferometer elevation angle measurement radar has its antennas tilted slightly relative to each other so as to detect differences in amplitude from ground return signals; the phase difference in signals (normally utilized as an indication of depression angle below boresight in an interferometer radar) is checked for a positive rate of change; it is then compared against amplitude differences and is accepted as valid for use in generating an elevation angle only if within prescribed limits thereof. This resolves ambiguity in phase which results from a wide spread of antennas with respect to the wavelength of the radar.
TL;DR: In this article, a combined schlieren interferometer is introduced, which makes use of the plasma itself as a beam-splitter, and the diagnostic value of Schlieren techniques is compared to that of interferometry.
Abstract: In rotationally symmetric plasmas one can determine the electron density profiles from refractive index effects, preferably by using infrared radiation. In this report the diagnostic value of schlieren techniques is compared to that of interferometry. As a very efficient diagnostic setup, a combined schlieren interferometer is introduced, which makes use of the plasma itself as a beam-splitter. Experimentally, arc plasmas are investigated using the infrared radiation of a CO2-laser at 10.6 mu wavelength.
TL;DR: The holo-diagram demonstrates the interference limits and diffraction limits of any method of optical information retrieval.
Abstract: Ordinary interferometry, hologram interferometry, contouring, speckle, moire, ordinary radar, Doppler radar, optical Doppler velocimeter, Doppler holography, and gated viewing are all discussed, and it is demonstrated how closely these methods are related to each other. One single diagram, the holo-diagram, can be used for the evaluation of each method and even for combinations of the methods. The diagram is constructed for the study of interference patterns when an object is placed in the vicinity of two focal points representing either one point of illumination and one point of observation or two points of illumination or two points of observation. It reveals interference surfaces in space and how ordinary interference fringes are formed where an object intersects these surfaces. With a common moire analogy the three-dimensional sensitivity distribution and the fringe patterns of each of the methods can be simulated. Finally it is pointed out that the diagram demonstrates the interference limits and diffraction limits of any method of optical information retrieval.
TL;DR: In this paper, the complete radiation pattern of a 25m diameter radio telescope has been measured at 21 cm wavelength to a level of 60 dB below the main beam response using an interferometer consisting of the radio telescope and a 7.5m diameter reference antenna.
Abstract: The complete radiation pattern of a 25-m diameter radio telescope has been measured at 21-cm wavelength to a level of 60 dB below the main beam response. Strong cosmic radio sources with known flux density were used as a signal source. The measurement employed an interferometer consisting of the radio telescope and a 7.5-m diameter reference antenna. By changing the orientation of the telescope, while keeping the reference antenna pointed at the source, the output voltage of the interferometer varies proportional to the field strength pattern of the telescope. This method provides a large improvement in sensitivity over a total power measurement. The paper discusses the theoretical basis of the technique. It describes the layout of the interferometer, the electronic equipment, and the methods of observation and reduction of the data. Some 19 000 points in the pattern were measured. The pattern is displayed by contour plots of equal level. The derived main characteristics of the telescope [1968 AD] at 1415 MHz are as follow: gain 49.0 \pm 0.2 dB, absorption area 282 \pm 8 m2, aperture efficiency 0.56, half-power beamwidth 0.57 \times 0.62\deg . The accuracy and detail allow astronomers to reliably correct radio astronomical observations for the effect of radiation in the sidelobes, spillover region, and feed support scatter lobes. Theoretical calculations of pattern parameters may be checked quantitatively.
TL;DR: In this paper, a holographic interferometer is used to obtain separate but simultaneous isochromatic and isopachic-fringe patterns for photoelastic models in states of plane stress.
Abstract: A shortcoming of the conventional holographic interferometer used in photoelasticity is that, for the double-exposure cases, the resulting fringe patterns are a complex combination of conventional isochromatic and isopachic fringes. This paper describes a holographic interferometer that may be used to obtain separate but simultaneous isochromatic- and isopachic-fringe patterns for photoelastic models in states of plane stress. The method requires a model with a partially reflecting front surface. Isopachics, which are proportional to the thickness change, are recorded using holographic interferometry from the transmitted light. The isochromatics are obtained from the transmitted light by conventional means. General equations relating the surface displacement of the specimen to the observed fringe patterns are developed, and examples of static and dynamic loadings are shown.