Showing papers on "Interferometry published in 1988"
TL;DR: In this paper, an approach to 'unwrapping' the 2 pi ambiguities in the two-dimensional data set is presented, where it is found that noise and geometrical radar layover corrupt measurements locally, and these local errors can propagate to form global phase errors that affect the entire image.
Abstract: Interferometric synthetic aperture radar observations provide a means for obtaining high-resolution digital topographic maps from measurements of amplitude and phase of two complex radar images. The phase of the radar echoes may only be measured modulo 2 pi; however, the whole phase at each point in the image is needed to obtain elevations. An approach to 'unwrapping' the 2 pi ambiguities in the two-dimensional data set is presented. It is found that noise and geometrical radar layover corrupt measurements locally, and these local errors can propagate to form global phase errors that affect the entire image. It is shown that the local errors, or residues, can be readily identified and avoided in the global phase estimation. A rectified digital topographic map derived from the unwrapped phase values is presented.
2,246 citations
TL;DR: The phase modulation in an interferometer can be induced by moving a mirror, tilting a glass plate, moving a grating, rotating a half-wave plate or analyzer, using an acoustooptic or electro-optic modulator, or using a Zeeman laser as mentioned in this paper.
Abstract: Publisher Summary This chapter describes the phase-measurement interferometry techniques. For all techniques, a temporal phase modulation is introduced to perform the measurement. By measuring the interferogram intensity as the phase is shifted, the phase of the wavefront can be determined with the aid of electronics or a computer. Phase modulation in an interferometer can be induced by moving a mirror, tilting a glass plate, moving a grating, rotating a half-wave plate or analyzer, using an acousto-optic or electro-optic modulator, or using a Zeeman laser. Phase-measurement techniques using analytical means to determine phase all have some common denominators. There are different equations for calculating the phase of a wavefront from interference fringe intensity measurements. The precision of a phase-measuring interferometer system can be determined by taking two measurements, subtracting them, and looking at the root-meansquare of the difference wavefront. The chapter discusses the simulation results. The elimination of the errors that reduce the measurement accuracy depends on the type of measurement being performed. Phase-measurement interferometry (PMI) can be applied to any two-beam interferometer, including holographic interferometers. Applications can be divided into: surface figure, surface roughness, and metrology.
1,340 citations
TL;DR: A first series of in vivo measurements acoustically determined eye length, with a multimode semiconductor laser, within a precision of 0.03 mm.
Abstract: With a multimode semiconductor laser we have been able to measure the optical length of the eye within a precision of 0.03 mm. A first series of inυiυo measurements of several human beings shows good correlation with the acoustically determined eye length.
654 citations
TL;DR: In this paper, the authors presented an alternative to real aperture measurements of the Earth's brightness temperature from low Earth orbit using a single interferometric measurement, and the noise characteristics of the brightness temperature image produced from the interferometer measurements are discussed.
Abstract: Interferometric aperture synthesis is presented as an alternative to real aperture measurements of the Earth's brightness temperature from low Earth orbit. The signal-to-noise performance of a single interferometric measurement is considered, and the noise characteristics of the brightness temperature image produced from the interferometer measurements are discussed. The sampling requirements of the measurements and the resulting effects of the noise in the measurements on the image are described. The specific case of the electronically steered thinned array radiometer (ESTAR) currently under construction is examined. The ESTAR prototype is described in detail sufficient to permit a performance evaluation of its spatial and temperature resolution. Critical aspects of an extension of the ESTAR sensor to a larger spaceborne system are considered. Of particular important are the number and placement of antenna elements in the imaging array. >
530 citations
TL;DR: A calibrated Fourier transform spectrometer, known as the High-Resolution Interferometer Sounder (HIS), has been flown on the NASA U-2 research aircraft to measure the infrared emission spectrum of the earth to meet high radiometric precision and accuracy requirements.
Abstract: A calibrated Fourier transform spectrometer, known as the High-Resolution Interferometer Sounder (HIS), has been flown on the NASA U-2 research aircraft to measure the infrared emission spectrum of the earth. The primary use - atmospheric temperature and humidity sounding - requires high radiometric precision and accuracy (of the order of 0.1 and 1 C, respectively). To meet these requirements, the HIS instruments, the HIS instrument performs inflight radiometric calibration, using observations of hot and cold blackbody reference sources as the basis for two-point calibrations at each wavenumber. Initially, laboratory tests revealed a calibration problem with brightness temperature errors as large as 15 C between 600 and 900/cm. The symptom of the problem, which occurred in one of the three spectral bands of HIS, was a source-dependent phase response. Minor changes to the calibration equations completely eliminated the anomalous errors. The new analysis properly accounts for the situation in which the phase response for radiance from the instrument itself differs from that for radiance from an external source. The mechanism responsible for the dual phase response of the HIS instrument is identified as emission from the interferometer beam splitter.
436 citations
TL;DR: It is shown that it may be made to further enhance the sensitivity within a narrow bandwidth, becoming tuned recycling, and the various sensitivity-bandwidth combinations, together with the tuning properties, are discussed.
Abstract: Laser interferometers may detect gravitational waves by sensing the strain in space produced by their passage. The resultant change in intensity of an interference fringe must be observable against a background noise due to the statistical fluctuations in the number of detected photons. Optimization of the detector sensitivity thus involves devising an optical system which both maximizes the signal and minimizes the noise. This is attempted in the various arrangements known collectively as light recycling. Here, the performance of these systems is quantitatively assessed. Standard or broadband recycling functions essentially by making efficient use of the available light, but it is shown that it may also be made to further enhance the sensitivity within a narrow bandwidth, becoming tuned recycling. This works, as do all the narrow-band variants, by arranging for both the laser light and a gravitational-wave-induced sideband to be resonant in the optical system. The original narrow-band system, resonant recycling, can also be made broadband; the various sensitivity-bandwidth combinations, together with the tuning properties of such a system, are discussed.
358 citations
TL;DR: A simple extension of the hypothesis of locality is used to determine the interference phase shift induced by the rotation of a neutron interferometer, which consists of the Sagnac term, which is due to the coupling of the orbital angular momentum of the neutron with the rotate of the frame.
Abstract: The physical basis for the description of phenomena by a rotating observer is investigated. A simple, yet tentative, extension of the hypothesis of locality is used to determine the interference phase shift induced by the rotation of a neutron interferometer. The result consists of the Sagnac term, which is due to the coupling of the orbital angular momentum of the neutron with the rotation of the frame, and a new term which arises from a similar coupling because of the neutron spin. The latter effect is generally smaller than the Sagnac phase shift by the ratio of de Broglie wavelength of the neutron to the dimension of the interferometer. The possibility of detecting the new effect is briefly discussed.
300 citations
TL;DR: In this paper, a force microscope using a fiber-optic interferometer as the cantilever displacement sensor is described, achieving a sensitivity of 1.7×10−4 A/(Hz)1/2 for frequencies above 2 kHz.
Abstract: A force microscope is described which uses a fiber‐optic interferometer as the cantilever displacement sensor. Low thermal drift and reduced susceptibility to laser frequency variation are achieved due to the small (several micrometer) size of the interferometer cavity. A sensitivity of 1.7×10−4 A/(Hz)1/2 is observed for frequencies above 2 kHz. The drift rate of the sensor is on the order of 3 A/min. As an initial demonstration, laser‐written magnetic domains in a thin film sample of TbFeCo were imaged.
285 citations
TL;DR: In this article, low-loss silica-based singlemode waveguides and directional couplers are fabricated on silicon substrates and their application to Mach-Zehnder interferometer type guided-wave devices is demonstrated.
Abstract: Low-loss silica-based single-mode waveguides and directional couplers are fabricated on silicon substrates. Their application to Mach-Zehnder interferometer type guided-wave devices is demonstrated. Optical switches or tunable optical couplers are fabricated using the thermooptic effect. Asymmetrical Mach-Zehnder interferometers are successfully applied to multi/demultiplexers for optical FDM transmission systems. >
264 citations
TL;DR: In this paper, a superheterodyne detection (SHD) technique is presented, which permits measurement of the phase difference of two optical frequencies that cannot be resolved by direct optoelectronic HD detection.
Abstract: In two-wavelength interferometry, synthetic wavelengths are generated in order to reduce the sensitivity or to extend the range of unambiguity for interferometric measurements Here a novel optoelectronic technique, called superheterodyne detection, is presented, which permits measurement of the phase difference of two optical frequencies that cannot be resolved by direct optoelectronic heterodyne detection This technique offers the possibility for operation of two-wavelength interferometry in real time with arbitrary synthetic wavelengths from micrometers to meters in length Preliminary experimental results are reported An optical arrangement for absolute range-finding applications using tunable-laser sources (eg, semiconductor lasers) is proposed
224 citations
Patent•
16 Sep 1988TL;DR: In this article, a two-mode optical waveguide with a non-circular core is used to provide stable spatial intensity patterns in both propagation modes for light propagating therein.
Abstract: An apparatus utilizes a two-mode optical waveguide with a non-circular core to provide stable spatial intensity patterns in both propagation modes for light propagating therein. The light has a wavelength, and the non-circular core has cross-sectional dimensions selected such that (1) the waveguide propagates light at that wavelength in a fundamental mode and a higher order mode, and (2) substantially all of the light in the higher order mode propagates in only a single, stable intensity pattern. Embodiments of the invention include, for example, modal couplers, frequency shifters, mode selectors and interferometers. One of the interferometer embodiments may be used as a strain gauge.
TL;DR: RefReflectively monitored Fabry-Perot interferometers which make use of dielectric mirrors in continuous lengths of single mode fiber are characterised for use as temperature and wavelength sensors as discussed by the authors.
Abstract: Reflectively monitored Fabry-Perot interferometers which make use of dielectric mirrors in continuous lengths of single mode fibre are characterised for use as temperature and wavelength sensors.
TL;DR: A detailed review of classical flow visualization methods can be found in this article, where Merzkirch and Lauterborn & Vogel present a beautiful collection of pictures by Van Dyke.
Abstract: Flow visualization results from the interaction between light and matter. Classical methods such as shadowgraphy, schlieren photography, and interferometry visualize variation in the index of refraction induced by changes in density, pressure, or temperature. Nonuniformities of these physical observables modify the phase of optical waves, rendered visible by free-space propagation (shadowgraphy), optical processing in the back focal plane of a lens (schlieren photography), or interference with a ref erence wave (interferometry). The classical methods visualize variations of the index of refraction or spatial derivatives thereof integrated along the light path through the fluid. Three-dimensional space is projected onto a plane with the corresponding reduction in degrees of freedom. Except for axial symmetric or two-dimensional flows, spatial structures cannot be recovered from a single image. Interior detail may be visualized by illuminating the flow with a sheet of light and imaging scattered radiation from variations in particle density or physical observables. Mie scattering is widely used because particles scatter more efficiently than molecules. Rayleighand Raman-scattering cross sections are small, necessitating intense laser sources for flow visu alization. Excellent reviews of classical flow-visualization methods have been pub lished, for example, by Merzkirch (1974) and Lauterborn & Vogel (1984) and a beautiful and inspiring collection of pictures by Van Dyke (1982).
TL;DR: This paper presents a meta-anatomy of the determinants of interferometry and their applications in optics, and some of the properties of these determinants have been described in more detail in a prior work.
Abstract: We report a direct experimental observation of Pancharatnam's phase, which is closely related to Berry's topological phase. The experiment involves measurement of the phase change in one beam of a laser interferometer as the polarization state of light is taken along a closed circuit on the Poincar\'e sphere. The phase change is found to be equal to half the solid angle subtended by the circuit at the center of the Poincar\'e sphere. Apart from providing a striking demonstration of the topological phase, the experiment demonstrates that unitary time evolution of a system is not essential for the appearance of the topological phase.
TL;DR: The phase shifting procedure enables the detection of most of the errors listed above by a special Lissajous display technique described here.
Abstract: The accuracy of phase shifting interferometers is impaired by mechanical drifts and vibrations, intensity variations, nonlinearities of the photoelectric detection device, and, most seriously, by inaccuracies of the reference phase shifter. The phase shifting procedure enables the detection of most of the errors listed above by a special Lissajous display technique described here. Furthermore, it is possible to correct phase shifter inaccuracies by using an iterative process relying solely on the interference pattern itself and the Fourier sums used in phase shifting interferometry.
TL;DR: In this article, a modified Michelson interferometer is used to study the strain properties of piezoelectric and electrostrictive materials, and a feedback loop is introduced to stabilize the system against the low-frequency optical path-length drifting and the system is capable of resolving displacements of the order of 10−3 A.
Abstract: A modified Michelson interferometer is used to study the strain properties of piezoelectric and electrostrictive materials. For small displacement, a feedback loop is introduced to stabilize the system against the low‐frequency optical path‐length drifting and the system is capable of resolving displacements of the order of 10−3 A. For the strain induced by domain switching, a dual‐channel signal detection scheme is used which automatically reads out the displacement of the sample. The effect on the measurement of the sample bonding to a substrate and other related problems are discussed.
TL;DR: In this paper, the relative merits of three designs of compound optical-fiber-based resonators for application to line narrowing in fiber lasers and demultiplexing in optical-communications systems are discussed.
Abstract: The relative merits of three designs of compound optical-fiber-based resonators for application to line narrowing in fiber lasers and demultiplexing in optical-communications systems are discussed. The three resonator designs are a set of concatenated rings, a three-reflector resonator with loop mirrors, and a fiber Fox–Smith interferometer.
Journal Article•
TL;DR: The Mark III interferometer as discussed by the authors is an operational long baseline stellar interferer on Mt. Wilson with four-possible baseline configurations from 9m NE-SW to 20m N-S.
Abstract: The Mark III interferometer is an operational long baseline stellar interferometer on Mt. Wilson with four-possible baseline configurations from 9m NE-SW to 20m N-S. The interferometer was designed to be a highly automated astronomical instrument to measure stellar positions and diameters to a magnitude limit of seven. Initial fringe observations were made in September 1986 with a 12-m N-S baseline. In the following months, semi-automated astrometric and stellar diameter measurements were also made. This paper describes the hardware and software components of the instrument and its operational characteristics. The interferometer has several novel features. One is the use of optimal estimation and control algorithms (e.g. Kalman filters) in the control loops. Another is the ability to operate both as a closed-loop phased interferometer and eventually as an open-loop or absolute coherent interferometer. High thermal stability and mechanical accuracy should permit the instrument to point blind at an astronomical object and maintain optical path equality to within the limits set by the atmosphere. In this absolute interferometric mode of operation, it should be possible to observe faint astronomical objects that are too dim for phase tracking. In theory, measurements of amplitude, group delay, and closure phase will be possible to 14 mag.
TL;DR: Direct measurements of the frequency dependence of the optical group delay for a number of optical components commonly used in femtosecond optics are reported, obtaining measurement accuracy of about ±1 fsec over the spectral range of 400–750 nm.
Abstract: We report direct measurements of the frequency dependence of the optical group delay for a number of optical components commonly used in femtosecond optics. We have investigated the group-delay errors that occur on reflection from metal and dielectric mirrors under various conditions and passage through devices that introduce angular dispersion. We obtain measurement accuracy of about ±1 fsec over the spectral range of 400–750 nm.
TL;DR: In this article, a planar diffraction gratings operating in high order was proposed for inertial sensors with sensitivities that exceed those of conventional mechanical sensors and multiple circuit optical interferometers by many powers of ten.
Abstract: This paper shows that matter-wave interferometers employing low-velocity neutral atoms can be used as inertial sensors with sensitivities that exceed those of conventional mechanical sensors and multiple circuit optical interferometers by many powers of ten. The energy and mass dependence of the phase shifts that are due to rotation and acceleration are different. Thus a pair of interferometers with different energies and/or masses can perform simultaneous independent measurements of rotation and acceleration. A proposed configuration is one formed by a sequence of planar diffraction gratings operating in high order. Gratings consist of near-resonant standing-wave laser beams. Laser decelerated and cooled atomic beams provide a suitable source. Path curvature due to acceleration and rotation is canceled by magnetic field gradients that produce an effective magnetic levitation of the atoms in a feedback arrangement that maintains null phase shift.
TL;DR: In this paper, the effects of input polarization on the output fringe visibility of two-beam interferometric fiber-optic sensors are investigated, and an analysis which predicts the existence of input states of polarization of eigenmodes of the interferometer for which optimum output visibility is obtained is presented.
Abstract: The effects of input polarization on the output fringe visibility of two-beam interferometric fiber-optic sensors are investigated, and an analysis which predicts the existence of input states of polarization of eigenmodes of the interferometer for which optimum output visibility is obtained is presented. Experimental results obtained using both a bulk-optic and a fiber Mach-Zehnder interferometer are reported that verify this analysis. Active feedback stabilization of the output fringe visibility of an interferometric sensor using automatic input-polarization control is demonstrated. >
TL;DR: A primary calibration method for ultrasonic hydrophones which uses a Michelson interferometer to determine the particle displacement in an ultrasonic field is discussed and results are in agreement with those of other methods and with the theoretically predicted frequency response of a hydrophone.
Abstract: A primary calibration method for ultrasonic hydrophones which uses a Michelson interferometer to determine the particle displacement in an ultrasonic field is discussed The acoustic pressure is derived from this measurement and used to determine the free-field sensitivity of a hydrophone in the frequency range 05-15 MHz The random uncertainty of the method is typically 1%, whereas the systematic uncertainty varies from 23 to 66% over the frequency range To obtain this accuracy, the performance of the system has been carefully examined and appropriate correction factors derived The greatest difficulty in the method lies in determining the frequency response of the optical detection system, and two different approaches have been used to measure this response Several acoustical effects have also been studied and the calibration procedure modified to take account of them The calibration results are in agreement with those of other methods and with the theoretically predicted frequency response of a hydrophone The method has been used to determine the temporal stability of a hydrophone over a period of two years >
TL;DR: A subaperture configuration to test aspheric optical components or systems has been developed that may eliminate the need to use null lenses for measuring some aspheres at the center of curvature.
Abstract: A subaperture configuration to test aspheric optical components or systems has been developed. The aperture is divided into annular subaperture regions, and an interferometer is refocused for each region to reduce the fringe density. The method is suited to phase-measuring interferometry and may be used with standard interferogram reduction software. The theoretical basis for the method, requirements for the number of annular zones, sensitivity to the selection of the number of polynomials, and tolerances for centration and radius are described. Numerical and experimental validations of the algorithm are described. The method may eliminate the need to use null lenses for measuring some aspheres at the center of curvature.
TL;DR: In this article, a novel principle for the design of correlation arrays is introduced, based upon the maximization of the distance between samples, which is applied to the problem of finding solutions for moderate numbers of elements (up to 12).
Abstract: A novel principle for the design of correlation arrays is introduced, based upon the maximization of the distance between samples. Simulated annealing is applied to the problem of finding solutions for moderate numbers of elements (up to 12). The resulting arrays have symmetric crystalline structures. >
TL;DR: In this paper, a sinusoidal phase modulation is introduced into one of the beams of the hologram interferometer to offset the argument of the Bessel-function fringes, which permits the evaluation of vibration amplitudes with the same facilities used for static displacements.
Abstract: A method of holographic vibration analysis is presented that permits the extraction of vibration amplitudes by means of measurements from a photodiode-array camera from time-average hologram reconstructions, concomitant (real-time) hologram interferometry, or a speckle interferometer with an electronic holography readout system. A sinusoidal phase modulation is introduced into one of the beams of the hologram interferometer to offset the argument of the Bessel-function fringes. Irradiance values from time-average interferograms with zero, plus, and minus offsets can be processed numerically by a method analogous to that used for cosine fringes from a phase-step interferometer. This permits the evaluation of vibration amplitudes with the same facilities used for static displacements. The mathematical theory of this process is presented.
TL;DR: A scanning soft x-ray microscope has been built and operated at the National Synchrotron Light Source as discussed by the authors, which makes use of a mini-undulator as a bright source of 3.2-nm photons.
Abstract: A scanning soft x‐ray microscope has been built and operated at the National Synchrotron Light Source. It makes use of a mini‐undulator as a bright source of 3.2‐nm photons. An electron beam fabricated Fresnel zone plate focuses the beam onto the specimen, which is scanned under computer control. The scanning stage can be moved by both piezoelectric transducers and stepping motors, and the location is monitored by a high‐speed laser interferometer. X rays transmitted through the specimen are detected using a flow proportional counter. Images of biological specimens and of artificial microstructures have been made with resolution in the 75–100‐nm range. Acquisition time for 256×256‐pixel images is about 5 min.
TL;DR: A new technique is proposed, in which the transport equation is solved by the Fourier transform method for a periodic boundary condition with high spatial carrier frequency, which is created by making a light beam with unknown phase distribution pass through a grating.
Abstract: Experimental demonstrations of deterministic phase retrieval based on the Teague-Streibl irradiance transport equation are presented. A new technique is proposed, in which the transport equation is solved by the Fourier transform method for a periodic boundary condition with high spatial carrier frequency, which is created by making a light beam with unknown phase distribution pass through a grating. Quantitative phase measurements were performed by experiments without recourse to interferometry, and the results were found to be in good agreement with theory.
TL;DR: In this paper, a multichannel, two-color, quadrature heterodyne interferometer is used to measure the line density in the DIII-D tokamak.
Abstract: A multichannel, two‐color, quadrature heterodyne interferometer is used to measure the line density in the DIII‐D tokamak. The unique feature of this real‐time vibration‐compensated interferometer is the combination of high speed (1 MHz), high resolution (2π/256), and wide range (±8193 fringes). Quadrature phase information from a CO2 laser (10.6 μm) and a He–Ne laser (0.63 μm) are digitized with high‐speed (6 MHz) flash digitizers. Zero crossings of the signals are counted with digital circuitry yielding quarter fringe resolution with a 4‐MHz bandwidth. Further fringe resolution of 1/256 is provided at 350 kHz by a PROM which uses the digital signals as input to a look‐up table. Analog line density is presently available at 80 kHz with a system noise equivalent phase shift of ±2/256. Error monitoring is provided for low signal amplitude and exceeding the maximum fringe rate. In addition, a method to prevent coating of in‐vessel mirrors due to plasma and vessel wall cleaning discharges has been developed.