Showing papers on "Interferometry published in 1974"
TL;DR: The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.
Abstract: A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.
1,206 citations
Journal Article•
921 citations
TL;DR: In this paper, the interference of two widely separated coherent neutron beams produced by dynamical diffraction in a perfect Si-crystal has been observed, and phase shifting material inserted in the beams results in a marked intensity modulation behind the interferometer.
400 citations
TL;DR: A Doppler shift in wavelength can result in a very slight change in the index of refraction of a transparent material due to disperison as mentioned in this paper, which produces an error of a few percent in the velocities determined using the recently developed velocity interferometer for diffusely reflecting surfaces.
Abstract: A Doppler shift in wavelength can result in a very slight change in the index of refraction of a transparent material due to disperison. This effect, if not accounted for, produces an error of a few percent in the velocities determined using the recently developed velocity interferometer for diffusely reflecting surfaces.
179 citations
Patent•
15 Jul 1974TL;DR: In this paper, an infrared radiation modulator comprising three parallely arranged interferometer plates, forming two successive slits or cavities therebetween for passing the infrared radiation to be modulated, is presented.
Abstract: An infrared radiation modulator comprising three parallely arranged interferometer plates, forming two successive slits or cavities therebetween for passing the infrared radiation to be modulated. The width of said slits is periodically varied by the oscillations of the central interferometer plate while the two outer plates remain stationary, a positive variation of the width of one of the slits corresponding at any time to a negative variation of the width of the other slit. A particularly suitable material for the interferometer plates is monocrystalline doped cadmium telluride having a high resistivity and a limited absorption rate for infrared radiation. A very precise alignment of the interferometer plates and an accurate adjustment of the width of the slits therebetween can be achieved by using a wedge-arrangement comprising three radially displaceable wedges disposed at angles of 120° for adjusting the parallelism of the plates and the width of the slits formed between the central plate and the two outer plates when in their normal (rest) position, said adjustment being made independently for each slit. In a particular embodiment, the interferometer plates are made of a material having a high resistance and having marginal zones overlaid with metal layers forming in each slit three uniformly distributed capacitors. By varying the capacitance of said capacitors the width of the interferometric slits or the parallelism of the plates can be adjusted.
168 citations
TL;DR: In this paper, a speckle-shearing interferometer was developed using a sheared Michelson interferometers, which utilizes the speck effect of coherent light.
134 citations
TL;DR: In this paper, the authors derived the closure phase relation for a three-element interferometer using data obtained from observations at 7.8 GHz of the radio sources 3C 273B and 3C 84 by antennas in Massachusetts, California, Alaska, and Sweden.
Abstract: The derived 'closure' phase relation for a three-element interferometer is used in a presented analysis of data obtained from observations at 7.8 GHz of the radio sources 3C 273B and 3C 84 by antennas in Massachusetts, California, Alaska, and Sweden (the first two antennas were used in combination with each of the last two separately to form two three-element interferometers). The brightness distribution is found for each source by expansion of both the fringe amplitude and the fringe phase in separate Fourier series.
125 citations
TL;DR: A grating lateral shear interferometer is described that can be used with a white light source and the use of the interferometers with certain types of extended sources is demonstrated.
Abstract: A grating lateral shear interferometer is described that can be used with a white light source. The use of the interferometer with certain types of extended sources is also demonstrated.
89 citations
TL;DR: Speckle-shearing interferometry as discussed by the authors is an interferometric method for flexural deformation, which does not require the surface of the specimen must be of mirror quality.
Abstract: A specimen illuminated by coherent light is imaged by a camera through a shearing mechanism so that the speckle from one point on the surface can be made to interfere with the speckle from a neighboring point. The resultant speckle pattern is recorded. By mechanically interfering the recorded speckle pattern corresponding to deformed and undeformed states of the specimen, respectively, using double-exposure technique, a speckle-moire-fringe pattern is generated. These fringes which depict derivatives of deflections of the specimen are made visible by spatial-filtering technique. Speckle-moire fringes can also be obtained in real time. This method is a new interferometry and will be referred to as “speckle-shearing interferometry”. Speckle-shearing interferometry has the same function as Ligtenberg's technique. However, it does not have the sometimes inconvenient requirement of Ligtenberg's technique that the surface of the specimen must be of mirror quality. The new technique will be particularly useful in studies of flexural deformation such as flexed beams and plates. Although speckle-shearing interferometry is an interferometric method, it overcomes several of the limitations associated with holographic and speckle interferometries, namely: (1) the setup is simple and does not need laborious alignments of optical components, (2) it does not require stringent mechanical and ambient stabilities, (3) coherent requirement of light is greatly relaxed, and (4) the sensitivity is reduced that somehow fills the gap in sensitivity between moire techniques and holographic or speckle interferometry.
82 citations
TL;DR: Holographic interferometry was used to find dynamic displacement of the surface of a sand half-space model excited by a harmonically vibrating circular footing as discussed by the authors, and the screening effectiveness of wave barriers composed of rows of vertical cylindrical holes was studied.
Abstract: Holographic interferometry was used to find dynamic displacement of the surface of a sand half-space model excited by a harmonically vibrating circular footing. The screening effectiveness of wave barriers composed of rows of vertical cylindrical holes was studied using this technique. The general results indicate that: (1) Holographic interferometry is a powerful tool for measurement of static as well as dynamic displacement of the surface of sand half-space model; and (2) stroboscopic, double exposure, holographic interferometry can be used to get "stopped motion" records of traveling waves. Specific results for barriers indicate that the scaled hole diameter (diameter/wave-length of Rayleigh wave) should be at least 1/6, the net scaled spacing ((c-c spacing - diameter)/wavelength) should be less than 1/4, and the solid-filled hole barriers behave fundamentally differently than fluid-filled or void holes. /ASCE/
80 citations
TL;DR: In this article, the infrared spectrum of nitrous oxide has been measured and analyzed from 3000 cm −1 to 8200 cm − 1, and the spectra have been recorded with the Fourier transform interferometer of Laboratoire Aime Cotton.
TL;DR: In this paper, a high sensitivity 337 μm HCN laser interferometer for plasma electron density measurements is described, which has a time resolution of 100 μsec and a sensitivity of 10 -2 fringe.
01 Mar 1974
Abstract: A camera having a lens with two apertures and equipped with a shearing mechanism is employed to image a specimen which is illuminated by coherent light. With this arrangement, the speckle from one point on the surface is allowed to interfere with the speckle from a neighboring point so that a speckle-grid pattern may be detected in the image plane. By double-exposure or real-time techniques, the speckle-grid pattern corresponding to the deformed state of the specimen is added to the speckle-grid pattern corresponding to the undeformed state of the specimen. The resulting mechanical interference produces a moire-fringe pattern which depicts derivatives of surface-displacements. The camera will be referred to as "Speckle-shearing Interferometric Camera". Three applications of the speckle-shearing interferometric camera are described: (1) mea-surement of slopes of structural deflections, (2) in-plane strain measurement, (3) vibration analy-sis. Experimental demonstrations for each case of the applications are presented. Although the speckle-shearing interferometric camera is based on interferometric principles, it overcomes several of the limitations associated with holographic and speckle interferometries, namely: (1) the setup is simple and does not re-quire laborous alignment of optical components, (2) it does not require stringent mechanical and ambient atmospheric stabilities, (3) coherent requirements of light are greatly relaxed, (4) the sensitivity is greatly reduced, and (5) it does not require differentiation to obtain strains.© (1974) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this paper, the authors used holographic interferometry to map isothermal contours in the developing convective plume above heated, horizontal, rectangular surfaces, and found that the thermal structure of the developing plume is strongly influenced by the partitioning of the flow adjacent to the surface along lines of geometric symmetry.
TL;DR: Construction details and operating characteristics are given for a narrowband pulsed dye laser system, pumped by a nitrogen laser, that offers very linear reproducible frequency tuning over continuous ranges of 150 GHz and more, at a bandwidth down to 25 MHz.
Abstract: Construction details and operating characteristics are given for a narrowband pulsed dye laser system, pumped by a nitrogen laser, that offers very linear reproducible frequency tuning over continuous ranges of 150 GHz and more, at a bandwidth down to 25 MHz. A diffraction grating in Littrow configuration, a tilted Fabry-Perot interferometer inside the cavity, and an optical external confocal filter interferometer are the wavelength-selective elements. Simultaneous scanning of these elements is accomplished without mechanically moving parts by changing the gas pressure in an enclosing chamber.
TL;DR: An interferometers designed to measure and/or generate angles with high precision and accuracy is described and the experimental performance of a prototype interferometer is discussed.
Abstract: An interferometer designed to measure and/or generate angles with high precision and accuracy is described. Design criteria and equations are developed and the experimental performance of a prototype interferometer is discussed.
TL;DR: In this article, the nonlinear refractive index coefficient n2 of each system component was measured at 1.06 μm using a time-resolved Mach-Zehnder interferometer.
Abstract: To properly account for nonlinear propagation effects in the design of a large laser system, it is necessary to know the nonlinear refractive index coefficient n2 of each system component. We report values of n2 for YAG, ED‐2 laser glass, EY‐1 Faraday rotator glass, and FR‐4 rotator glass. The measurements were made at 1.06 μm using a time‐resolved Mach‐Zehnder interferometer to directly observe the variation of refractive index with intensity during the transmission of pulses 150 psec in duration.
TL;DR: A developed form of the Fresnel zone-plate interferometer is described, associated with the real and virtual first order foci of a zone plate, and its properties are discussed.
Abstract: A developed form of the Fresnel zone-plate interferometer is described. Three basic configurations are distinguished, associated with the real and virtual first order foci of a zone plate. Related versions and higher order variants are also educed. Compensated phase zone plates used in this application are found to produce uniform amplitude wavefronts. The properties of the interferometer in this form are discussed and an example given of its high-quality performance.
TL;DR: In this article, the Laue-case skew-symmetric two-crystal X-ray interferometer is described, and the alignment is accomplished with an auxiliary Xray beam, which is multiply reflected by both interferometers parts.
Abstract: The construction and successful operation of a Laue-case skew-symmetric two-crystal X-ray interferometer is described. The alignment is accomplished with an auxiliary X-ray beam, which is multiply reflected by both interferometer parts. As expected, the skew-symmetric two-crystal interferometer is found to be considerably less affected by vibrations than is the symmetric two-crystal interferometer. [Bonse & te Kaat (1968), Z. Phys. 214, 16–21]. The dependence of the crystal lattice moire pattern on rotations about the Δρ and Δθ axes are investigated.
TL;DR: In this paper, amplitude interferometry was used to measure the diameters of four late-type giant stars, alpha Boo, alpha Ori, alpha Tau, and beta Peg.
Abstract: Diameters are reported for four late-type giant stars, alpha Boo, alpha Ori, alpha Tau, and beta Peg. The diameters were obtained with a new kind of interferometer designed expressly to operate in the presence of atmospheric fluctuations. The new technique, called amplitude interferometry, is briefly described. The results include measurements of alpha Ori at several wavelengths.
TL;DR: Experimental observations of large particle signals generated by the passage of a particle through the interference pattern of a laser interferometer show that particle size can be determined from analysis of the signal.
Abstract: Experimental observations of large particle signals generated by the passage of a particle through the interference pattern of a laser interferometer are reported. The results show that particle size can be determined from analysis of the signal. The influence of large particle sizes in determining the velocity of the particle from the signal is discussed.
TL;DR: In this article, the authors examined the theory and applications of Fourier transform spectroscopy and applied it to high-resolution infrared spectrography of astronomical objects using a Michelson interferometer.
Abstract: Publisher Summary This chapter examines the theory and applications of Fourier transform spectroscopy. A Michelson interferometer is ideally suited for work in high-resolution infrared spectroscopy of astronomical objects. In this application the available signal-to-noise ratio limits the number of observable objects and, therefore, any gain in signal-to-noise is of tremendous importance. The Michelson interferometer is a device for interfering two beams of light. Light entering the interferometer is divided into two separate beams by a beam splitter and is recombined after a controllable phase delay has been applied to one of the beams The use of digital computers in performing the Fourier transform of the interferogram, implies that the data be supplied in digital form. The effect of the slow-beat frequency is to make the contributions from spectral elements near the calculated element essentially positive rather than averaging to zero. The dispersive properties of the beam splitter can cause wave number-dependent phase shifts. The data recording and processing systems are as important as the optical and mechanical systems of the interferometer.
TL;DR: In this paper, a modified Ronchi interferometer using two identical gratings is described, which is suitable for the measurement of small, zonal aberrations, since the shear can be changed continuously by rotating one grating with respect to the other, while the direction and magnitude of the tilt between the sheared wavefronts can be varied by adjusting the distances of the two gratings from the centre of the gaussian sphere.
TL;DR: In this article, two widely separated coherent neutron beams from dynamical diffraction in a perfect Si-crystal are used for neutron interferometric measurements, where Al and Bi samples cause phase shifts within the individual beams which result in a marked intensity oscillation of the interfering beams behind the E-shaped interferometer crystal.
Abstract: Two widely separated coherent neutron beams from dynamical diffraction in a perfect Si-crystal are used for neutron interferometric measurements. Al and Bi samples cause phase shifts within the individual beams which result in a marked intensity oscillation of the interfering beams behind theE-shaped interferometer crystal. With this interferometer interesting features of various physical quantities can be investigated in a new way, e.g. refracting index, scattering amplitudes, magnetic domain structures, density inhomogeneities, and coherence properties of the neutron beams.
TL;DR: In this article, a servo controlled Fabry-Perot interferometer using capacitance micrometers to sense departures from parallelism and variations in the mean spacing of the Fabry Perot plates is described.
Abstract: A servo controlled Fabry-Perot interferometer using capacitance micrometers to sense departures from parallelism and variations in the mean spacing of the Fabry-Perot plates is described. The parallelism and mean spacing of the plates is maintained over the full 75 mm aperture of the instrument to an accuracy better than the surface quality of the plates ( approximately lambda /150 at 500 nm).
TL;DR: A coherence interferometer, an instrument discussed by the author whose principles have been discussed by others, has been assembled and has undergone successful preliminary tests at Kitt Peak National Observatory, and is used for complex amplitude interferometry.
Abstract: Astronomical observations requiring high spatial resolution made from the surface of the earth are affected by atmospheric turbulence. There is currently considerable interest in the interaction of light from astronomical sources with the earth's atmosphere. 1,2 This Letter reports results using one particular technique for predetection processing of astronomical data. A coherence interferometer, an instrument discussed by the author whose principles have been discussed by others, has been assembled and has undergone successful preliminary tests at Kitt Peak National Observatory. Others have considered a similar type of instrument for intensity interferometry. Here it is used for complex amplitude interferometry. Theory of operation, a brief discussion of alignment, comments on its method of operation, and some scientific results are given. The instrument is capable of a real time analog display of the real part of the two-dimensional Fourier transform of a self-luminous, white light (broadband), unpolarized source. It is necessary that the source be spatially incoherent. The core of the instrument is a simple, glass prism Twyman-Green interferometer, with roof reflectors in place of plane mirrors. Roofs are at right angles to each other so the field into one arm is flipped top to bottom, and the field into the other arm is flipped left to right. This prism is positioned in the instrument pupil space. Figure 1 shows a schematic view of the instrument. Plane 3 is an image plane and contains a stop that limits the area over which processing takes place. Lens 5 collimates light from the image plane and relays the telescope entrance aperture (pupil) into roofs of the prism at plane 6. Lens 8 relays an image of the roof onto the detector plane 11. Halfway between plane 8 and 11 is a secondary image plane. The letter F is shown here to demonstrate the mapping properties of the interferometer between the image plane 3 and 8'. A single element of area in plane 3 is mapped into two elements in plane 8'. Each of the two elements at plane 8' is an image of the same source element, radiation from each is coherent with that from the other, and these points contribute to fringes of high contrast at the detector plane 11. A consequence of the mapping properties of the interferometer is to produce in the final observation plane a fringe pattern for each element of area in plane 3. The orientation of the fringes is determined by
TL;DR: In this paper, a Michelson interferometer was used for the measurement of low-frequency vibrational amplitudes in the sub-angstrom range (down to 10−3 A) as a function of temperature.
Abstract: A Michelson interferometer is described for the measurement of low‐frequency vibrational amplitudes in the sub‐angstrom range (down to 10−3 A) as a function of temperature. For this purpose a temperature stabilizing circuit has been developed. The use of a condensor microphone as an electromechanical feedback transducer opens up the possibility to relate the amplitude measurements to the wavelength of light. By these means the accuracy, reliability, and versatility of the interferometer are considerably improved and the draw‐backs of existing set ups are effectively eliminated.