Showing papers on "Astronomical interferometer published in 1989"
TL;DR: In this article, a high-sensitivity fiber-optic displacement sensor for atomic force microscopy is described based on the optical interference occurring in the micron-sized cavity formed between the cleaved end of a singlemode optical fiber and the microscope cantilever.
Abstract: A high‐sensitivity fiber‐optic displacement sensor for atomic force microscopy is described. The sensor is based on the optical interference occurring in the micron‐sized cavity formed between the cleaved end of a single‐mode optical fiber and the microscope cantilever. As a result of using a diode laser light source and all‐fiber construction, the sensor is compact, mechanically robust, and exhibits good low‐frequency noise behavior. Peak‐to‐peak noise in a dc to 1 kHz bandwidth is less than 0.1 A. Images are presented demonstrating atomic resolution of graphite and magnetic force imaging of bits written on a magnetic disk.
634 citations
TL;DR: An experiment is described in which the step size of a stepper-motor-driven translation stage was measured by recording the spectrum of light output from an interferometer and performing a cross-correlation calculation with theoretical spectra.
Abstract: A technique is presented for measuring small displacements by observing the frequency of spectral modulation of white light in a Michelson interferometer. An experiment is described in which the step size of a stepper-motor-driven translation stage was measured by recording the spectrum of light output from an interferometer and performing a cross-correlation calculation with theoretical spectra. Measurements made using standard laboratory-quality optical equipment were accurate to within ~10 nm for a range of over 100 microm.
255 citations
TL;DR: In this paper, a polarizing optical interferometer was developed for force microscopy, where the deflection of the force-sensing cantilever is measured by means of the phase shift of two orthogonally polarized light beams.
Abstract: We present a polarizing optical interferometer especially developed for force microscopy. The deflections of the force‐sensing cantilever are measured by means of the phase shift of two orthogonally polarized light beams, both reflected off the cantilever. This arrangement minimizes perturbations arising from fluctuations of the optical path length. Since the measured quantity is normalized versus the reflected intensity, the system is less sensitive to intensity fluctuations of the light source. The device is especially well suited to static force measurements. The total rms noise measured is ≲0.01 A in a frequency range from 1 Hz to 20 kHz.
200 citations
TL;DR: This work demonstrates the potential of solitons as the natural bits in ultrafast optical processing by observing switching of 93% of the total reflected energy in a partially transmitting integrated fiber loop mirror that makes up the interferometer.
Abstract: We demonstrate, for the first time to our knowledge, the switching of optical solitons. We observe switching of 93% of the total reflected energy in a partially transmitting integrated fiber loop mirror that makes up the interferometer. This result demonstrates the potential of solitons as the natural bits in ultrafast optical processing.
193 citations
TL;DR: In this article, a multichannel far-infrared interferometer used on the Joint European Torus (JET) is described, with emphasis on features necessitated by remote handling requirements, fluctuations in atmospheric humidity, and unmanned automatic operation.
Abstract: A multichannel far‐infrared interferometer used on the Joint European Torus (JET) is described. The light source is a 195‐μm DCN laser. The instrument is of the Mach–Zehnder type, with a heterodyne detection system. The modulation frequency (100 kHz) is produced by diffraction from a rotating grating. There are six vertical and two oblique channels. The latter rely on retroreflection from mirrors mounted on the vessel wall. Their vibration is compensated by a second wavelength interferometer at 118.8 μm. The various subsystems are described, with emphasis on features necessitated by (a) large path lengths, (b) remote handling requirements, (c) fluctuations in atmospheric humidity, and (d) unmanned automatic operation. Typical measurements, along with real‐time and off‐line data analysis, are presented. The phase‐shift measurement is made with an accuracy of (1)/(20) of a fringe, corresponding to a line‐integrated electron density of 5×1017 m−2. Comparison with other electron density diagnostics are shown. The introduction of additional optics allows measurements of the Faraday effect and a determination of the poloidal magnetic field distribution. The signal processing and data analysis are described. Errors introduced by the calibration procedure, birefringence of the probing beams, toroidal field pickup, the flux geometry, and the density profile are considered. The Faraday angle is measured with an accuracy of 5% and a time resolution of 1–10 ms. The poloidal magnetic field is deduced with an accuracy of ±15%.
122 citations
TL;DR: In this paper, a double beam laser interferometer is built up to study high-frequency piezoelectric and electrostrictive strains, which is capable of resolving a displacement of 10−2 A using lock-in detection and measuring the strain all the way to the resonance frequencies using a digital oscilloscope for detection.
Abstract: A double beam laser interferometer is built up to study high‐frequency piezoelectric and electrostrictive strains. The system is capable of resolving a displacement of 10−2 A using lock‐in detection and measuring the strain all the way to the piezoelectric resonance frequencies using a digital oscilloscope for detection. The interference of sample bending to the detected signal is effectively avoided.
111 citations
TL;DR: A novel accelerometer in which the sensing element is a weighted diaphragm that is measured using a miniature hemispherical air-spaced Fabry-Perot interferometer, of which one mirror is mounted on the diphragm.
Abstract: We describe a novel accelerometer in which the sensing element is a weighted diaphragm. The displacement of the diaphragm produced by acceleration is measured using a miniature hemispherical air-spaced Fabry-Perot interferometer, of which one mirror is mounted on the diaphragm. The interferometer is illuminated by a diode laser and addressed through a monomode optical fiber.
95 citations
TL;DR: A new technique that provides linear measurement of dynamic phase change in a no-feedback, no-phase-bias fiber-optic interferometer is described and is unaffected by random changes in phase, source intensity, and fringe visibility.
Abstract: A new technique that provides linear measurement of dynamic phase change in a no-feedback, no-phase-bias fiberoptic interferometer is described. The phase measurement is unaffected by random changes in phase, source intensity, and fringe visibility. A minimum detectable phase shift of 0.1 rad has been measured for the configuration reported.
86 citations
29 Jan 1989
TL;DR: A long-trace optical profiling instrument is now in operation at Brookhaven National Laboratory measuring surface figure and macro-roughness on large optical components, principally long cylindrical mirrors for use in synchrotron radiation beam lines as discussed by the authors.
Abstract: A new long-trace optical profiling instrument is now in operation at Brookhaven National Laboratory measuring surface figure and macro-roughness on large optical components, principally long cylindrical mirrors for use in synchrotron radiation beam lines. The non-contact measurement technique is based upon a pencil-beam interferometer system. The optical head is mounted on a linear air bearing slide and has a free travel range of nearly one meter. We are able to sample surface spatial periods between 1 mm (the laser beam diameter) and 1 m. The input slope data is converted to surface height by a Fourier filtering technique which distributes the random noise error contributions evenly over the entire trace length. A number of optical components have been measured with the instrument. Results are presented for fused silica cylinders 900 mm and 600 mm in length and for a fused silica toroid and several electroless nickel-plated paraboloids. 9 refs., 8 figs.
85 citations
01 Jan 1989
TL;DR: In this paper, an overview of phase closure imaging methods for high-angular resolution optical interferometry is presented, including the Papa Detector and the Knox-Thompson Algorithm.
Abstract: I: Basic principles.- to Fourier Optics and Coherence.- Optical Propagation and Image Formation Through the Turbulent Atmosphere.- Radio Telescopes: Basic Concepts.- Continuously Movable Telescopes for Optical Interferometry.- II: Module and phase estimation, image reconstruction.- Amplitude Estimation from Speckle Interferometry.- Notes on Noise Calibration of Speckle Imagery.- Amplitude Estimation from Diluted Array Interferometry.- First Order Imaging Methods: An Introduction.- Speckle Imaging with the Papa Detector and the Knox-Thompson Algorithm.- Phase Closure Imaging - Theory & Practice.- Speckle Masking, Speckle Spectroscopy, and Optical Aperture Synthesis.- Merits of Phase Restoration Methods.- Pupil-Plane Interferometry.- Real-Time Wavefront Sensing and Adaptive Optics.- Differential Interferometry.- Image Restoration.- Deconvolution Ancient and (Very) Modern.- III: Scientific and technical prospects.- Astrophysical Programs for High Angular Resolution Optical Interferometry.- Frontiers of Interferometry.- Perspectives in Optical Interferometry.- IV: Contributed seminars and posters.- Cophasing Telescope Arrays.- Some Thoughts on the Combination of Beams in Interferometers Using Telescopes of Unequal Size.- Real-Time Image Sharpening.- Scasis, Diffraction-Limited Imaging Using a Redundant Pupil Plane-Interferometer.- Aperture Synthesis in Space: Overview and Results from the Esa Study Group.- Estimation and Reconstruction from Aberrated Amplitude Interferometer Measurements.- Lunar Occultations or Milliarcsecond Resolution and Their Relation to Interferometric Techniques at Present and in Future.- List of posters.
79 citations
TL;DR: In this article, a 1 m optical fiber Sagnac interferometer with a pump power of 24 W at a wavelength of 532 nm was used to switch an optical signal at 632 nm.
Abstract: Switching in less than 1 ns of an optical signal at 632 nm is demonstrated in a 1 m optical fiber Sagnac interferometer. Full signal modulation was obtained with a pump power of 24 W at a wavelength of 532 nm.
TL;DR: A new type phase locked interferometer which uses tunability of the wavelength of a laser diode and uses a CCD image sensor as a photodetector to scan electrically a measuring point along the surface of the object.
Abstract: We propose a new type phase locked interferometer which uses tunability of the wavelength of a laser diode. The phase lock is achieved by controlling the injection current of the laser diode. A CCD image sensor is used as a photodetector to scan electrically a measuring point along the surface of the object. Since this interferometer uses no mechanical elements such as a piezoelectric transducer and galvanomirror, the measurement accuracy is not limited by the mechanical properties. The characteristics of the feedback control system for the phase lock are examined through measurements of surface profiles of the diamond-turned aluminum disks.
01 Jul 1989
TL;DR: The significance of radio astronomy at millimeter and sub-millimeter wavelengths is described in this article, and some of the more important results are given, including the limitations imposed by the atmosphere and the observation techniques used to overcome these limitations.
Abstract: The significance of radio astronomy at millimeter and submillimeter wavelengths is described, and some of the more important results are given. The limitations imposed by the atmosphere are discussed, and the observation techniques used to overcome these limitations are outlined. The major new millimeter and submillimeter telescopes are described, and the techniques used to construct large-diameter, high-precision antennas are discussed. Methods of measuring the surface of a high-precision antenna are described with particular emphasis on microwave holography. The current state of the high-sensitivity receiving systems for these wavelengths is outlined with emphasis on recent work in superconducting devices and multibeam receivers. A brief description of astronomical millimeter-wave interferometers is given, and the recent progress made in the application of very-long-baseline interferometry techniques at millimeter wavelengths is described. >
TL;DR: In this article, a small dielectric particle in a focused monochromatic light beam produces a scattered wave (Rayleigh scattering) in phase quadrature with the far field incident beam, therefore causing a phase shift in this beam.
Abstract: The detection of subtenth micron paticles in processing fluids is a critical and growing need in the semiconductor industry. In this letter, we show that a small dielectric particle in a focused monochromatic light beam produces a scattered wave (Rayleigh scattering) in phase quadrature with the far‐field incident beam, therefore causing a phase shift in this beam. Thus, the forward scattered field due to the particle may be detected using a bright field interferometer. This allows detection which is near Shott noise limited even for very small particles, and measures the sign of the scattered field as well, such that particles may be distinguished from bubbles. We describe an appropriate interferometer design based on Nomarski optics, which we have used to verify our calculation, measuring scattering in water from single polystyrene spheres as small as 0.038 μm in diameter.
31 Jan 1989
TL;DR: In this paper, thin viscoelastic layers with active-matrix addressing are proposed as high-resolution spatial light modulators (SLM's) for eventual use in a reflective schlieren light valve.
Abstract: Thin viscoelastic layers with active-matrix addressing are proposed as high-resolution spatial light modulators (SLM's) for eventual use in a reflective schlieren light valve. Light modulation is achieved by diffraction from the periodically deformed mirror electrode covering the SLM layer. A two-dimensional array of Si-MOS transistors will be employed for addressing the viscoelastic SLM. Orthogonal and diagonally offset arrangements of pixels with two grating periods each are suggested for this active matrix. For measuring the deformation behavior of viscoelastic layers with a reflective top electrode, a standard microscope interferometer was modified so that the phase-shift technique could be employed. The deformation profile is recorded by means of a CCD image sensor, while the temporal development of the deformation is detected with a photomultiplier tube. Qualitatively, the experimental results agree with previously obtained predictions from an extensive theoretical analysis of the SLM's time behavior and spatial-frequency response.
TL;DR: All-optical switching with femtosecond and picosecond pulses is demonstrated in a single-fiber interferometer in which the role of the two arms is played by two mutually delayed versions of the same pulse.
Abstract: All-optical switching with femtosecond and picosecond pulses is demonstrated in a single-fiber interferometer in which the role of the two arms is played by two mutually delayed versions of the same pulse. This technique eliminates thermal and acoustic imbalances of the interferometer.
TL;DR: Methods based on the closure phase now allow imaging of complex objects in the presence of severe aberrations and are vital to the success of modern, high-resolution astronomical imaging both at radio and at optical wavelengths.
Abstract: Closure phase is a number measured by triplets of Michelson interferometers that is completely independent of certain types of otherwise severe instrumental errors. In the 30 years since closure phase was invented, it has been applied to a diverse number of different problems in astronomical imaging. Methods based on the closure phase now allow imaging of complex objects in the presence of severe aberrations and are vital to the success of modern, high-resolution astronomical imaging both at radio and at optical wavelengths. Over the past 10 to 15 years, the concept of closure phase has been extended and generalized. One of the most important advances has been the development of automatic or self-calibration techniques. This article reviews closure phase methods and some of the many spin-offs and related ideas.
TL;DR: In this paper, the interference pattern was obtained from the actual amplitude and phase of the interfering wave fronts at the exit aperture of the interferometer, and the excess of the period of the output signal was obtained in a closed form in the case of small misalignment and negligible difference between the optical paths.
Abstract: In optical interferometers illuminated by laser sources the shift of the phase and changes in the curvature of the wave fronts lead to systematic errors, to which there must be added the error caused by misalignments. In the study described in the present article, the interference pattern was obtained from the actual amplitude and phase of the interfering wave fronts at the exit aperture of the interferometer. With reference to plane-wave illumination, the excess of the period of the output signal was obtained in a closed form in the case of small misalignment and negligible difference between the optical paths.
TL;DR: In this article, the fabrication and assembly of a rotational shearing interferometer with variable shear and phase compensation is described, which has been used for seeing measurements and interferometric imaging in optical astronomy.
Abstract: The fabrication and assembly of a compact rotational shearing interferometer with variable shear and phase compensation is described. The interferometer has been used for seeing measurements and interferometric imaging in optical astronomy.
TL;DR: A phase-conjugate interferometer is described that is self-referencing, compact, and insensitive to environmental disturbances, provides twice the sensitivity of conventional interferometers, and produces a direct representation of an incident wave front.
Abstract: We describe a phase-conjugate interferometer that consists of a partially transmitting conventional mirror placed in front of and in close proximity to a phase-conjugate mirror. The interferometer is self-referencing, compact, and insensitive to environmental disturbances, provides twice the sensitivity of conventional (nonphase-conjugate) interferometers, and produces a direct representation of an incident wave front. We have constructed such a device using internally self-pumped phase conjugation in barium titanate and have used the device to characterize the wave front produced by an aberrated optical system.
TL;DR: It has been determined that the x((3)) value of colloid semiconductor glass OG530 at 532 nm is 7 x 10(-12) esu.
Abstract: We have constructed a new interferometer that uses two phase-conjugate mirrors. This device allows for the measurement of the relative phase shift and the ratio of the nonlinear susceptibilities of materials. We have been able to measure weak reflectivity signals not detectable by normal degenerate four-wave mixing methods. It has been determined that the χ(3) value of colloid semiconductor glass OG530 at 532 nm is 7 × 10−12 esu.
TL;DR: This tunable differential interferometer has several advantages over other methods for phase measurements in optical tomography, including good stability, variable sensitivity, and the elimination of fringe ambiguity.
Abstract: We report the use of a tunable differential interferometer for optical tomography. This interferometer has several advantages over other methods for phase measurements in optical tomography, including good stability, variable sensitivity, and the elimination of fringe ambiguity. Quantitative images of the gas concentrations in subsonic jets of methane and oxygen issuing into air are presented, with absolute accuracies better than 3.5% and 4.5%, respectively.
23 May 1989
TL;DR: In this article, a compact and portable moire interferometer is used to determine surface deformations of an object, which is comprised of a laser beam, optical and fiber optics devices coupling the beam to one or more evanescent wave splitters, and collimating lenses directing the split beam at one or several specimen gratings.
Abstract: A compact and portable moire interferometer used to determine surface deformations of an object. The improved interferometer is comprised of a laser beam, optical and fiber optics devices coupling the beam to one or more evanescent wave splitters, and collimating lenses directing the split beam at one or more specimen gratings. Observation means including film and video cameras may be used to view and record the resultant fringe patterns.
01 Jan 1989
TL;DR: In this paper, a multichannel scanning interferometer designed for tomographically inferring contours of electron density in magnetically confined plasmas is described, where the scanning element is a multisectored blazed rotating grating, which emerges at a different angle from each sector, giving rise to a fan array of discrete beams for each rotation of the grating.
Abstract: A novel multichannel scanning interferometer designed for tomographically inferring contours of electron density in magnetically confined plasmas is described. The scanning element is a multisectored blazed rotating grating. The diffracted beam emerges at a different angle from each sector, giving rise to a fan array of discrete beams for each rotation of the grating. Signals from the probing chords are multiplexed in time enabling the use of a single detecting element for the extraction of many channels of line‐integrated density information. An air‐turbine‐driven grating wheel assembly has been fabricated and initial tests performed. The proposed interferometer is to operate at 337 μm and will be installed on the H‐1 helical axis stellarator currently under construction at the Australian National University.
TL;DR: In this paper, the authors describe a number of multiplexing techniques which may be used for fiber-optic sensors in which the sensing element is a ring resonator, which can be used to yield a sensor of increased sensitivity over that obtainable with a two-beam interferometer.
Abstract: We describe a number of multiplexing techniques which may be used for fibre-optic sensors in which the sensing element is a ring resonator. The basic optical unit comprises a sensing ring resonator connected to a second interrogating ring resonator of nearly equal length, and illuminated by a source of short coherence length. A number of such units may be combined to form an array, using coherence multiplexing techniques. Using such an arrangement, the high finesse of the ring resonator may be exploited to yield a sensor of increased sensitivity over that obtainable with a two-beam interferometer. When a high-coherence source is used, then multiplexing may be accomplished using frequency-division techniques. However, in this case, the resonators must have low finesse, in order to avoid cross-talk. We also show that when a source of moderate coherence length is used, it is possible to use both frequency division and coherence multiplexing simultaneously, with the potential of realizing a large sen...
25 Jul 1989
TL;DR: In this article, a dual measurement interferometer was developed specifically for wafer stage metrology, which concurrently measures both linear and angular displacement, and was designed to conserve space, minimize stage mass, eliminate heat sources and provide high resolution and slew rate.
Abstract: A dual measurement interferometer has been developed specifically for wafer stage metrology. The interferometer concurrently measures both linear and angular displacement. It is designed to conserve space, minimize stage mass, eliminate heat sources and provide high resolution and slew rate.
TL;DR: In this paper, a monolithic parallel spring mechanism with fiexture hinges was used to calibrate the motion of the scanner with sub-nanometer accuracy in real time.
Abstract: We have developed a new STM using monolithic parallel spring mechanisms with fiexture hinges. The STM is equipped with a two-dimensional optical interferometer to calibrate the motion of the scanner with subnanometer accuracy in real time. Distortion-free images of a grating pattern have successfully been observed.
Patent•
06 Nov 1989
TL;DR: In this paper, the phase retardation between the arms of the interferometer is modulated using small applied AC voltages to detect wavelength shifts in a broad-bandwidth optical source.
Abstract: An integrated-optics wavelength stabilization device for broad-bandwidth optical sources requires small-optical-path-difference interferometers to detect wavelength shifts. The phase retardation between the arms of the interferometer is modulated using small applied AC voltages.
21 Mar 1989
TL;DR: A wide range of noncontact optical profilometers have been described in recent years, based on a variety of principles such as interferometry, local slope measurement, and focus detection as discussed by the authors.
Abstract: A wide range of non-contact optical profilometers has been described in recent years, based on a variety of principles such as interferometry, local slope measurement, and focus detection. The performances of these instruments can be compared by considering their ability to measure sinusoidal profiles, and mapping the limitations in amplitude-wavelength (AW) space.Relevant parameters depend on the design of the particular instrument. The numerical aperture of an objective lens, the maximum density of fringes that may be resolved, and the directional (angular) stability of a laser beam are examples of parameters that directly affect performance. Other relevant factors in optical, just as stylus, instruments are the ranges and resolutions of scanning motions, and the quality of a straight datum. AW maps are presented and compared for a number of different types optical probes instru ments, and comparisons are made with conventional stylus instruments. 1. INTRODUCTION
TL;DR: A novel accelerometer in which the sensing element is a weighted diaphragm designed to have minimal cross coupling, and the output of the two interferometers is processed such that the detrimental effects caused by wavelength drift of the source and variation in temperature of the sensor are reduced.
Abstract: We describe a novel accelerometer in which the sensing element is a weighted diaphragm designed to have minimal cross coupling. The displacement of the diaphragm, produced by acceleration, is measured by using two miniature hemispherical air-spaced Fabry–Perot interferometers, one constructed on either side of the diaphragm. The output of the two interferometers is processed such that the detrimental effects caused by wavelength drift of the source and variation in temperature of the sensor are reduced by 45.8 and 27.3 dB, respectively, compared with those of a single interferometer.