Showing papers on "Interferometry published in 1977"
TL;DR: In this article, a simple method (speckle masking) for the reconstruction of real images from astronomical speckle photographs is described, which is applicable to a restricted class of objects that includes double stars.
334 citations
TL;DR: In this paper, a single-mode optical fiber was used to pass a laser beam through a tank in which an approximately plane acoustic wave was produced, and the response of an optical fiber in water to low-frequency acoustic waves was investigated experimentally and compared with analytical results.
Abstract: The response of an optical fiber in water to low‐frequency acoustic waves was investigated experimentally and compared with analytical results. A single‐mode optical fiber was used to pass a laser beam through a tank in which an approximately plane acoustic wave was produced. A change in the optical index of refraction of the fiber creates an effective path‐length change for the optical beam which results in a phase shift of the optical beam with respect to a reference beam unaltered by the acoustic field. By mixing the phase‐shifted beam with a reference beam of constant phase in a photodetector the phase variation at the acoustic frequency is detected. Theoretically, the sensitivity of a fiber‐optic interferometer should be independent of frequency. Experimental results confirm this.
213 citations
TL;DR: Determination of an unknown length from the measured fractional fringes is aided by the development of analytical equations for the length and its uncertainty, and criteria are given for selecting the wavelengths.
Abstract: The development of stabilized multifrequency lasers makes fractional fringes an increasingly attractive technique for length measurement. Determination of an unknown length from the measured fractional fringes is aided by the development of analytical equations for the length and its uncertainty, and criteria are given for selecting the wavelengths.
138 citations
TL;DR: In this paper, a transverse displacement inteferometer (TDI) was used to monitor the transverse motion of the rear surface of a ycut quartz target plate in a plate-impact experiment.
Abstract: A new transverse‐displacement inteferometer (TDI) is described. This interferometer makes use of intensity variations of a beam obtained by superposition of two beams diffracted symmetrically from a diffraction grating copied onto a plane surface. The TDI is used to monitor the transverse motion of the rear surface of a y‐cut quartz target plate in a plate‐impact experiment. For this application, a 200‐line/mm grating is copied onto the rear surface of the target plate. The normal motion of the rear surface is monitored by means of a standard Michelson interferometer in which the zeroth‐order diffracted beam is used as the beam reflected from the moving mirror. The transverse motion is monitored simultaneously by means of a TDI employing the two fourth‐order diffracted beams, with a resulting sensitivity of 0.625 μm per fringe. The recorded motion confirms the predicted features of two coupled elastic waves, each involving both normal and transverse motion.
130 citations
107 citations
97 citations
TL;DR: A new method for real-time detection and measurement of small vibrations, based on phase modulation in time-average electronic speckle pattern interferometry, is described, which can study the deformation of the object in slow motion.
Abstract: We describe a new method for real-time detection and measurement of small vibrations, based on phase modulation in time-average electronic speckle pattern interferometry. The modulation frequency is shifted relative to the vibration frequency, which makes the intensity of the reconstructed image vary at the difference frequency. The amplitude detection limits are about 20 A by visual observation and 0.1 A by photoelectric measurement using a lockin technique. No auxiliary system for fringe stabilization is required. At higher amplitude levels we can study the deformation of the object in slow motion. Measurements on different objects, including human ear preparation, are presented.
94 citations
TL;DR: A method is presented for high-range resolution measurement of the backscatter from a scattering medium located in one arm of an interferometer that relies on the availability of a cw laser with a significant linewidth.
Abstract: A method is presented for high-range resolution measurement of the backscatter from a scattering medium located in one arm of an interferometer. The technique is interferometric in nature and relies on the availability of a cw laser with a significant linewidth. The measurement is based on observing coherent interference (equivalent to white-light fringes) between the return from the two arms of the interferometer for the portion of the backscatter that makes the path lengths equal. Experimental results are presented for backscatter from a turbid medium and from a stack of glass plates.
84 citations
TL;DR: In this article, a laser interferometer developed at NPL for thermal expansion measurement exploits the high resolution and accuracy of laser inter-ferometry in a dilatometer design which places a minimum of restrictions on the shapes and dimensions of specimens which can be measured.
Abstract: The dimensional changes produced in materials by temperature variations are generally very small, so that sensitive measuring techniques must be used to observe them. The interferometer developed at NPL for thermal expansion measurement exploits the high resolution and accuracy of laser interferometry in a dilatometer design which places a minimum of restrictions on the shapes and dimensions of specimens which can be measured. The presentation of thermal expansion data is discussed and relationships between the relevant parameters are derived. Many different materials have been investigated and some results of interest are included here.
73 citations
66 citations
TL;DR: In this paper, a survey of interferometric techniques receiving the optical path in real-time is presented, using differential interferometry or a new phase coupling technique, which can be obtained in a wide range of conditions.
Abstract: A survey is made of interferometric techniques receiving the optical path ? = ?nds in real time. Using differential interferometry or a new phase coupling technique, ?(t) can be obtained in a wide range of conditions. A variety of applications to gasdynamic problems is described.
TL;DR: In this paper, the Fabry-Perot interferometer on board of the OGO-6 satellite was used to measure the spectral profile of the 630 nm airglow line.
TL;DR: Measurements of the Fresnel-Fizeau effect in a fiber ring interferometer gyroscope are reported, leading to determination of maximum pulse rate transmitted through single-mode fibers.
Abstract: Measurements of the Fresnel-Fizeau effect in a fiber ring interferometer gyroscope are reported. The presence of the dispersion term in the Fresnel drag coefficient was discernable. The temperature dependence of the coefficient bears on the temperature sensitivity of the optical fiber gyroscope. An alternate approach to measuring fiber dispersion is an added benefit, leading to determination of maximum pulse rate transmitted through single-mode fibers.
01 Jul 1977
TL;DR: An analysis of the lateral shearing interferometer is given for laser beams to enable a simple determination of the local radius of curvature of the wavefront.
Abstract: An analysis of the lateral shearing interferometer is given for laser beams. The results enable a simple determination of the local radius of curvature of the wavefront. In addition, the presence of phase distortion in the beam may be ascertained.
TL;DR: In this article, a modified Mach-Zehnder interferometer employing a linearly polarized scene beam and a circularly polarized reference beam generates signals proportional to the sine and cosine of the phase shift introduced by the plasma.
Abstract: An interferometer has been developed with which it is possible to make accurate plasma density measurements in the presence of density gradients. A modified Mach–Zehnder interferometer employing a linearly polarized scene beam and a circularly polarized reference beam generates signals proportional to the sine and cosine of the phase shift introduced by the plasma. The differential sensitivity of the phase shift measurements is independent of the instantaneous phase angle, and the phase angle may be unambiguously followed through multifringe excursions of the interferometer. The phase shift measurement is also independent of fringe contrast fluctuations caused by the refractive bending of the scene beam by the plasma.
TL;DR: Scalar diffraction theory and experimental data are presented to show how the size information in the forward- scattered light is dependent on the collection optics geometry, including the size and shape of source beam stops, which have been neglected in previous analyses.
Abstract: The theory and conditions are summarized under which single spherical particles in the size range of a few micrometers and larger may be sized using the observed fringe visibility in a cross-beam laser velocimeter. Scalar diffraction theory and experimental data are presented to show how the size information in the forward-scattered light is dependent on the collection optics geometry, including the size and shape of source beam stops, which have been neglected in previous analyses. Experimental data are also presented to show that backscattered light may not be usable for this method of sizing in the range of sizes examined.
TL;DR: In this paper, an interferometric system for continuously measuring specimen velocity is described, where the Doppler shift of a laser beam reflected from the free surface is transformed into a variation of the diameter of Fabry-Perot interference rings, and the evolution of diameter versus time is continuously recorded by a streak camera.
Abstract: An interferometric system for continuously measuring specimen velocity is described. The Doppler shift of a laser beam reflected from the specimen’s free surface is transformed into a variation of the diameter of Fabry–Perot interference rings, and the evolution of the diameter versus time is continuously recorded by a streak camera. Two examples of the use of this system for study of shock waves are given to show the accuracy of this device.
TL;DR: In this article, a multichannel interferometer, designed for tokamak plasma density measurements, is described, where the phase shift experienced by the probing beam is transferred to a low-frequency signal obtained by Doppler shifting the frequency of the reference beam.
Abstract: A multichannel interferometer, designed for tokamak plasma-density measurements, is described. The phase shift experienced by the probing beam is transferred to a low-frequency signal obtained by Doppler shifting the frequency of the reference beam. This ensures a sensitivity of 10−2 fringe. The source is a cw HCN waveguide laser, with a 150-mW-output power. Eight channels are in operation on TFR. The variation of the line density as a function of time for each channel is deduced from the phase shift measurement by an on-line computer.
TL;DR: In this paper, a Michelson interferometer modified to track the fringe motion caused by atmospheric turbulence was proposed for relative stellar position measurements with 10-4 arcsec accuracy, where the fringe amplitude and phase measurements at two wavelengths are used to correct atmospheric distortion when the field of view is much larger than the isoplanatic patch.
Abstract: A proposed astrometric interferometer capable of relative stellar position measurements with 10-4 arcsec accuracy is described. The instrument is a long-baseline Michelson interferometer modified to track the fringe motion caused by atmospheric turbulence. Simultaneous fringe amplitude and phase measurements at two wavelengths are used to correct atmospheric distortion when the field of view is much larger than the isoplanatic patch. Relative positions of stars brighter than ~ 10 mag in an ~ 1° field of view can be measured with an accuracy of ~10-4 arcsec after several hours of observation. Such an instrument should have a number of interesting astrophysical and geophysical applications, such as a search for planets around nearby stars, the gravitational deflection of light around the sun, and changes in the earth’s axis of rotation.
TL;DR: A passive interferometer of low thermal expansion material, Cer-Vit, along with nonkinematic design and thermally compensated mirror mounts is constructed to achieve long term stability without the use of a servo control device.
Abstract: A multipass plane parallel Fabry-Perot interferometer (FPP-M) can give extremely high contrast
(in excess of 106) over a wide range of finesse values without reducing the transmission
significantly. Curves and tables are provided along with a brief outline of Chabbal’s
analysis for the residual defects of the Fabry-Perot mirrors to aid a quick assessment of the
optimum parameters for a desired spectrometric work. The exploitation of the advantages of an FPP-M
depends upon the maintenance of its stability. So, we have constructed a passive interferometer of
low thermal expansion material, Cer-Vit, along with nonkinematic design and thermally compensated
mirror mounts to achieve long term stability without the use of a servo control device.
TL;DR: In this paper, it was shown that the autocorrelation function of a telescope diffraction-limited image is closely approximated by a subtraction of the mean cross correlation of pairs of speckle photographs from the mean auto-correlation of the same set of data.
TL;DR: The theory and performance of a two beam differential interferometer for measurement of both surface and bulk waves are described in this article, which is insensitive to small errors (< 1 mm) in focus or in specimen flatness.
Abstract: The theory and performance of a two beam differential interferometer for measurement of both surface and bulk waves are described. The system is insensitive to small errors (<1 mm) in focus or in specimen flatness. Both amplitude and phase measurements are demonstrated. The system has been absolutely calibrated and can detect 6 × 10−4 A surface wave displacements on glass.
TL;DR: A method of temporal encoding of optical information is reported, leading to a consideration of the output of spectroscopic devices as a Temporal Fourier Hologram (TFH) and image processing by temporal holography.
Abstract: Assuming some parallelism between space and time variables, namely, in the frequency domain, that occurs in the description of optical signals as functions of space or/and space and time, the Abbe theory applies to temporal distributions. The concept of temporal response of any optical system, space invariant, working at the time frequency nu = c/lambda, is then brought out. A method of temporal encoding of optical information is also reported, leading to a consideration of the output of spectroscopic devices as a Temporal Fourier Hologram (TFH). This applies to metrology (interferometry in white light, surface testing, roughness measurements) and image processing by temporal holography. Holograms of extended self-luminous objects have been recorded in white light, and reconstructed images are presented.
TL;DR: In this article, a theoretical analysis of de-correlation effects in plane strain sensitive speckle pattern interferometry is presented, and it is shown that in-plane translations and out-of-plane rotations typically of order 102 μm and 10-3 radians respectively may be tolerated before fringe visibility becomes unacceptable.
Abstract: A theoretical analysis of de-correlation effects in plane strain sensitive speckle-pattern interferometry is presented. Experimental results supporting the theoretical model are summarized and it is shown that in-plane translations and out-of-plane rotations typically of order 102 μm and 10-3 radians respectively may be tolerated before fringe visibility becomes unacceptable. The results also indicate how the interferometer may be optimized. Interferograms which show the strain fields resulting from machining are presented.
TL;DR: In this paper, a theoretical investigation of the de-correlation of speckle pattern with change of wavelength has been performed with particular reference to the electronic Speckle-pattern interferometer.
Abstract: A theoretical investigation of the de-correlation of speckle pattern with change of wavelength has been performed with particular reference to the electronic speckle-pattern interferometer. A method of measuring surface roughness using speckle de-correlation is proposed and some preliminary results presented. In addition, the loss of fringe visibility in two-wavelength speckle-pattern interferometric contouring is investigated and experimental confirmation of the theory given.