Showing papers on "Astronomical interferometer published in 1971"
TL;DR: The Michelson interferometer, IRIS-D, was used on Nimbus 4 in April 1970 to record the thermal emission spectra of the earth with a nominal spectral resolution of 2.8 cm−1 and a noise equivalent radiance between approximately 0.5 and 1 erg sec−1 cm−2 ster− 1 cm as discussed by the authors.
Abstract: The Michelson interferometer, IRIS-D, flown on Nimbus 4 in April 1970 is an improved version of the interferometer, IRIS-B, flown on Nimbus 3 a year earlier. Thermal emission spectra of the earth are being recorded between 400 cm−1 and 1600 cm−1 with a nominal spectral resolution of 2.8 cm−1 and a noise equivalent radiance between approximately 0.5 and 1 erg sec−1 cm−2 ster−1 cm. This paper describes the design and performance of the IRIS-D and concentrates on the design differences that exist between the interferometers flown on Nimbus 3 and 4. The performance is demonstrated by examples of spectra obtained while in earth orbit.
77 citations
TL;DR: In this article, the practical realisation of phase modulation in interferometers designed for use with broad-band sub-millimetre-wave radiation is described, and the technique has been applied both in Fourier spectrometry and metrology.
48 citations
TL;DR: In this article, positive feedback has been used within a double Josephson junction quantum interferometer to achieve a current amplification which can be adjusted from outside the cryostat over the range 1-100.
Abstract: Positive feedback has been used within a double‐Josephson‐junction quantum interferometer to achieve a current amplification which can be adjusted from outside the cryostat over the range 1–100. The interferometer may be regarded as a three‐terminal amplifying device.
46 citations
TL;DR: In this article, the replacement of amplitude modulation by phase modulation in interferometers designed for refraction measurements using a laser source is shown to give a considerable increase in accuracy which is between one and two orders of magnitude of a Mach-Zehnder interferometer.
30 citations
TL;DR: In this paper, a computer program for handling the data is described, and the preferred mode of operation multiplexes the Mossbauer spectrum, velocity, and timing signals onto a single record.
27 citations
TL;DR: A 2.695 MHz survey of radio sources in a narrow strip of declination has recently been completed with the Jodrell Bank Mk II radio telescope (full details will be published later). Accurate positions for all the 74 sources have been measured with the RRE Malvern 2,695 MHz interferometer.
Abstract: A 2,695 MHz survey of radio sources in a narrow strip of declination has recently been completed with the Jodrell Bank Mk II radio telescope (full details will be published later). Accurate positions for all the 74 sources have been measured with the RRE Malvern 2,695 MHz interferometer. Using these positions and a transparent overlay technique of identification the relative positions of radio and optical objects were located on the National Geographic‐Palomar Sky Survey prints with an r.m.s. error of 4 arc s. In the 24 h of right ascension covered by the survey, twenty-three identifications with stellar objects have been made; among these are two remarkably bright (14.5 magnitude) objects, separated by less than two degrees in the sky, which may be worthy of special attention. Finding charts for these two objects are shown in Fig. 1.
25 citations
01 Aug 1971
TL;DR: Mars IR spectra with Connes-type interferometer, noting atmospheric absorption and albedo drop due to surface water as mentioned in this paper, showed that surface water was a major contributing factor.
Abstract: Mars IR spectra with Connes-type interferometer, noting atmospheric absorption and albedo drop due to surface water
22 citations
TL;DR: In this paper, a holographic interferometer suitable for the precise measurement of heat transfer is described, where interference occurs between beams which have traversed the same optical components and hence these components need not be of high quality.
Abstract: A holographic interferometer suitable for the precise measurement of heat transfer is described. In this instrument interference occurs between beams which have traversed the same optical components and hence these components need not be of high quality. Compared with the conventional Mach‐Zehnder interferometer, the present instrument is less expensive and simpler to construct, and yet the two interferometers yield comparable accuracy. For illustration, the holographic interferometer is used to study the free convection thermal boundary layer on a heated isothermal vertical flat plate. The results are in good agreement with an existing theory.
21 citations
Patent•
21 Jun 1971TL;DR: In this paper, an interferometric rotation sensor and control system is provided which includes a compound prism interferometer and an associated direction control system, where light entering the interferometers is split into two paths with the light in the respective paths being reflected an unequal number of times and then being recombined at an exit aperture in phase differing relationship.
Abstract: An interferometric rotation sensor and control system is provided which includes a compound prism interferometer and an associated direction control system. Light entering the interferometer is split into two paths with the light in the respective paths being reflected an unequal number of times and then being recombined at an exit aperture in phase differing relationship. Incoming light deviating from the optical axis of the device by an angle alpha causes a similar displacement of the two component images at the exit aperture with the result being that a fringe pattern is developed with the number of fringes being directly related to the angle alpha . Various control systems incorporating the interferometer are also disclosed.
10 citations
TL;DR: In this paper, the fractional fringe technique was used to estimate the electron density line integrals of 3.3×1012 cm−2 or lower with a wave length of 337 μ.
Abstract: An HCN laser‐interferometer is reported with better than 1/100 of a fringe phase shift sensitivity at a wave‐length of 337 μ. Applied to plasma density measurement this corresponds to electron density line integrals of 3.3×1012 cm−2 or lower. The fractional fringe technique involves sinusoidally driving the reference path mirror in a focused Michelson interferometer; changes in the effective path length alter the relative magnitude of even and odd harmonics in the resultant interferometer signal. Results are shown from application of this diagnostic to the Burnout V plasma.
7 citations
TL;DR: In this paper, a summary of interferometry techniques for direction finding, angular spectrum, angular width, and coherence ratio measurements and reviews the evolution of inter-ferometers for propagation research are presented.
Abstract: The transform relation between the field distribution and the angular spectrum forms the basis for the application of interferometry to propagation research. It is convenient to divide interferometry into instrumental combination and transform techniques which measure these Fourier relations to provide propagation mode resolution in terms of direction and angular width. Conventional direction-finder instrumentation represents the limiting case of single plane wave solution to the interference field. Computer instrumented interferometers and sampling arrays provide the capability for more general wave field analysis based on non plane wave models. This paper is a summary of interferometry techniques for direction finding, angular spectrum, angular width, and coherence ratio measurements and reviews the evolution of interferometers for propagation research. The reference list includes works from the radio astronomy and propagation literature relevant to fundamental interference analysis and interferometer instrumentation.
01 Jan 1971
TL;DR: In this article, solid Fabry-Perot narrow-band filters were constructed for H-alpha systems with one arc second or better resolution, with a three-inch aperture and a typical transmission rate of 70 per cent.
Abstract: We have constructed solid Fabry-Perot narrow-band filters that can be used in systems having one arc second or better resolution. Our filters operate at H-alpha, have a three-inch aperture, and typical transmission of 70 per cent. However, the same technology can be applied to construction of filters as narrow as 0.05 A at any wavelength from 4200 to 11000 A.
TL;DR: The stellar intensity interferometer has been used to measure a few cool giants and supergiants but, for technical reasons, attempts to develop it further have not proved successful.
Abstract: A difficult problem in observational optical astronomy is to measure the extremely small angles subtended at the Earth by the discs of stars. There are three techniques; Michelson's stellar interferometer, the stellar intensity interferometer at Narrabri, and lunar occultations. Michelson's interferometer has been used to measure a few cool giants and supergiants but, for technical reasons, attempts to develop it further have not, so far, proved successful. The stellar intensity interferometer is capable of very high resolving power and is unaffected by atmospheric seeing. It has been used to make all the existing measurements on hot stars. The present instrument at Narrabri in Australia is limited to stars brighter than magnitude + 2.5 and hotter than 6500°K (spectral type K5). A larger instrument could be built which would open up many new and interesting possibilities. The method of lunar occultations is comparatively simple and inexpensive. The accuracy of the results is still uncertain becau...
TL;DR: In this paper, the Covington-Drane optical synthetic apertures and the segmented thin annulus are discussed as a special case of the thin continuous annulus, and experiments are performed by masking a diffraction limited lens with the appropriate pupil function and then measuring the imaging characteristics of the aperture.
Abstract: Experimental and theoretical results are given for the one and two-dimensional Covington-Drane optical synthetic apertures and the thin annular aperture. The segmented thin annulus is also discussed as a special case of the thin continuous annulus. Experiments are performed by masking a diffraction-limited lens with the appropriate pupil function and then measuring the imaging characteristics of the aperture. All the synthetic apertures are shown to have the full synthetic MTF's predicted by the theory. The Covington-Drane doubles the resolution of the central aperture and the thin annular apertures synthesize the full lens spatial frequency response. Optical processing of synthetic aperture photography is discussed and examples of inverse spatial filters are given.
TL;DR: In this article, the authors investigated the use of Fabry-Perot interferometers with birefringent elements between the mirrors for dye laser reflection in the central mode.
TL;DR: In this article, a method for improving the sensitivity of an optical interferometer is described, which is based on dividing the electrical output of the interferometers by a voltage proportional to the incoming light intensity.
Abstract: A method is described for improving the sensitivity of an optical interferometer. The method is to divide the electrical output of the interferometer by a voltage proportional to the incoming light intensity. The resultant ratio is independent of incoming light intensity and also suppresses fluctuations in the interferometer output due to fluctuations in the incoming light. Using this technique, noise suppression by a factor of 50 has been obtained in a Mach‐Zehnder type interferometer. Larger factors should be obtainable. It is shown how the same technique can be applied to other types of interferometers.
TL;DR: In this article, a solid Fabry-Perot interferometer used as a monochromator at the Mees Solar Observatory is described, and a test exposure of the green (λ 5303) corona over a small active region is discussed.
Abstract: Characteristics of a solid Fabry-Perot interferometer used as a monochromator at the Mees Solar Observatory are described, and a test exposure of the green (λ 5303) corona over a small active region is discussed.
TL;DR: In this article, the authors calculated the tolerance on wavelength stability for frozen-fringe holography with a carefully designed interferometer and an object only 2 cm thick, within the control exercised by a well-designed resonant reflector.
Abstract: The tolerance on wavelength stability for frozen-fringe holography is calculated. It is convenient to split the effect into three terms: (1) the interferometric term that depends on the path difference between the reference beam and the signal beam, (2) the holographic term that represents the difference of wave-front curvature between signal and reference beams at the hologram plate, and (3) a lateral-displacement term. It is highly desirable to reduce to a minimum all the differences mentioned and to keep down the lateral-displacement term. To do this, new designs of holographic interferometers are proposed. With a carefully designed interferometer and an object only 2 cm thick, the wavelength tolerances are within the control exercised by a well-designed resonant reflector.
Patent•
12 Jan 1971
TL;DR: In this article, a solid state multiplier for an analogue computer which permits the unique determination of the bearing and elevation angles of arrival of a signal ray is presented, which provides solutions to a set of interferometer descriptive equations corresponding to data supplied by three two-element interferometers and a central-crossed Adcock array.
Abstract: A solid state multiplier for an analogue computer which permits the unique determination of the bearing and elevation angles of arrival of a signal ray. The multiplier provides solutions to a set of interferometer descriptive equations corresponding to data supplied by three two-element interferometers and a central-crossed Adcock array.
TL;DR: In this paper, a mechanical ''symmetrizer'' was built for use with far infrared interferometers driven by stepping motors, which allows convenient and consistent setting of the position of zero phase difference and thereby permits straightforward Fourier analysis of the measured one-sided (even) interferogram.
Abstract: A mechanical ``symmetrizer'' has been built for use with far infrared interferometers driven by stepping motors. It allows convenient and consistent setting of the position of zero phase difference and thereby permits straightforward Fourier analysis of the measured one‐sided (even) interferogram.
01 Sep 1971
TL;DR: The relationship between the size of an antenna and its resolving power has been studied in this paper, where it is shown that the largest fully steerable antennas used as radio telescopes have dimensions of at most a few thousand times their minimum useable wavelength; as a result the beamwidth of such instruments, and hence the angular resolving power, is at best a few minutes of arc.
Abstract: Radio astronomers, in common with many others who work with radio antennas, have always felt rather handicapped by the basic physical relationship between the size of an antenna (measured in wavelengths) and its resolving power (or beamwidth): ΔΘ ~ λ/D, where ΔΘ is the beamwidth in radians, λ the wavelength and D the diameter of the aperture. The largest fully-steerable antennas used as radio telescopes have dimensions of at most a few thousand times their minimum useable wavelength; as a result the beamwidth of such instruments, and hence the angular resolving power, is at best a few minutes of arc.
TL;DR: In this article, two phase-switched interferometers are described for the study of ionospheric irregularities by recording the amplitude scintillations in the flux of the radio stars, Cas A and Cyg A.
Abstract: We describe here two-element phase-switched interferometers built for the study of ionospheric irregularities by recording the amplitude scintillations in the flux of the radio stars, Cas A and Cyg A. Two interferometers have been built. The 110 MHz interferometer has been operating at Ahmedabad and the 74 MHz one, which is an improved version of Ahmedabad unit, has been operating at Gulmarg. The 110 MHz interferometer has been described in some detail and improvements incorporated in the 74 MHz interferometer are briefly discussed. The 110 MHz interferometer consists of two Yagi antennas, spaced ten wavelengths apart, connected to a superhet receiver. A half wavelength transmission line is switched in and out, at the rate of 340 Hz, between one of the antennas and the input of the receiver, which modulates the signal received from a radio source of small angular size. The fringe pattern of such an interferometer is relatively insensitive to the cosmic noise background, because it is an extended radio sou...
30 Jun 1971
TL;DR: In this article, a simulation game to train data processors in optimal data recovery techniques is presented, where three basic motions are required to modulate the wavelength and angular coordinates of the source.
Abstract: : A Simulation Game to train data processors in optimal data recovery techniques is included in this report. Also, the authors studied the triple- multiplexing response to a point source for a future scanning spectrometer. Three basic motions are required to modulate the wavelength and angular coordinates of the source. When performing preliminary experiments with the Multiplex Scanner, the authors discovered that the underlying Talbot effect is useful also for measuring phase objects. The theory of this new Talbot Interferometer is explored and experimental results of a candle flame are reported. For axially symmetric objects, this setup is modified by replacing the straight line gratings with circular gratings. In this way the radial gradient of the deformed wavefront is observed. Finally a means of simply, yet accurately collimating a light source using the Talbot Interferometer is described.
TL;DR: In this article, the sensitivity of an interferometer for optical thickness measurement can be reduced by passing both the beams through the sample but at different angles, and a method of compensation is described, to make the effective widths of the two beams equal at the sample surface.
Abstract: It is shown that the sensitivity of an interferometer for optical thickness measurement can be reduced by passing both the beams through the sample but at different angles. A method of compensation is described, to make the effective widths of the two beams equal at the sample surface. This technique allows the sensitivity of an interferometer to be varied over a wide range and is suitable for use with samples of thickness less than 1 mm. Two interferometers with reduced sensitivity are described; one of these is a Twyman-Green type and the other is a Mach-Zehnder type. At reduced sensitivity the interferometers do not give correctly the thickness variation in a sample which has an appreciable curvature. The precautions to be taken for testing such samples are discussed.