Showing papers on "Interferometry published in 1981"

Quantum Mechanical Noise in an Interferometer

Abstract: The interferometers now being developed to detect gravitational waves work by measuring the relative positions of widely separated masses. Two fundamental sources of quantum-mechanical noise determine the sensitivity of such an interferometer: (i) fluctuations in number of output photons (photon-counting error) and (ii) fluctuations in radiation pressure on the masses (radiation-pressure error). Because of the low power of available continuous-wave lasers, the sensitivity of currently planned interferometers will be limited by photon-counting error. This paper presents an analysis of the two types of quantum-mechanical noise, and it proposes a new technique---the "squeezed-state" technique---that allows one to decrease the photon-counting error while increasing the radiation-pressure error, or vice versa. The key requirement of the squeezed-state technique is that the state of the light entering the interferometer's normally unused input port must be not the vacuum, as in a standard interferometer, but rather a "squeezed state"---a state whose uncertainties in the two quadrature phases are unequal. Squeezed states can be generated by a variety of nonlinear optical processes, including degenerate parametric amplification.

Determination and correction of quadrature fringe measurement errors in interferometers

Abstract: The precision and accuracy of interferometers using quadrature fringe detection are often limited not by the interferometer itself but by the detector system. There are three typical errors: unequal gain in the two channels; quadrature phase shift error; and zero offsets. This paper describes a simple method for determining the quadrature errors from experimental data obtained in the interferometer and correcting for them. A numerical example demonstrating the significant improvement in the precision of interferometer data is given.

Sagnac effect in fiber gyroscopes

Abstract: We review the kinematic explanation of the Sagnac effect in fiber gyroscopes and recall that the index of the dielectric medium does not have any influence. Furthermore, we present a novel electrodynamic approach that confirms in more detail that the Sagnac phase shift of a ring-waveguide interferometer is the same as for the original Sagnac experiment with plane waves in a vacuum.

Radar interferometry: A new technique for studying plasma turbulence in the ionosphere

Abstract: A new radar interferometer technique has been developed and used successfully at the Jicamarca Radio Observatory in Peru to study the strong nighttime plasma turbulence in the equatorial electrojet. The technique represents a major step forward in radar probing of turbulent irregularities such as (but not limited to) those in the electrojet. In many situations it provides far more information than previous Doppler measurements. We form the cross spectrum of the backscattered signals received from approximately overhead on two antennas, separated in this case along an east-west baseline, as well as the individual power spectra. From the phase of the cross spectrum at different Doppler frequencies we can determine the individual positions of plasma wave packets propagating vertically with different velocities, and we find, for example, that oppositely propagating waves always come from distinctly separated regions. The data allow us to study the eddy structure within the electrojet in far more detail than hitherto possible, and by using the irregularity patches as tracers and following their east-west motion, we can obtain a vertical profile of drift velocity. Our first observations of this sort have shown that at night the vertical Doppler velocity at times may substantially exceed the mean horizontal velocity of the patch and the small horizontal velocity near the top and bottom of the layer may actually be westward when the main motion is eastward.

Optical techniques for on-line measurement of surface topography

Abstract: Optical techniques have great potential for non-destructive and on-line measurements of surface roughness during manufacturing. This paper reviews the state-of-the-art in a number of optical techniques including specular reflectance, total integrated scatter, diffuseness, angular scattering distributions, speckle, ellipsometry, and interferometry. The distinction is drawn between the more quantitative but slower profiling techniques and less quantitative, parametric techniques, which are faster and hence more useful for high-speed monitoring of surfaces. Overall, no currently available technique combines accuracy and speed and is therefore suitable as an on-line metrological tool for roughness measurement of engineering surfaces. Speckle techniques hold perhaps the greatest potential as accurate, high-speed metrological tools

General properties of lossless beam splitters in interferometry

Abstract: The author uses spinor algebra to investigate general properties of lossless beam splitters in interferometry.(AIP)

Construction and alignment of a high performance multipass vernier tandem Fabry–Perot interferometer

Abstract: A multipass vernier tandem Fabry–Perot interferometer is easily constructed and aligned when the two scanning mirrors are mounted on a common scanning stage. Using such a system we obtain an ultimate resolution of 10−3cm−1 and a maximum scanning range, free of overlapping orders, of ≳50 cm−1. Using a 5 plus 4 pass arrangement a contrast ≫10 is obtained which, together with a high overall luminosity, permits simultaneous resolution of both weak spectral features near zero energy shift and low‐frequency Raman bands. In addition to constructional details of this system we discuss the alignment procedure for uniform transmission in tandem operation, and demonstrate how the alignment requirments ultimately limit the performance of any tandem system to an ’’effective finesse’’ of <1000. Spectra showing surface waves in silicon and shear waves in polystyrene illustrate the power of this technique.

The Fabry-Perot Interferometer on Dynamics Explorer

Abstract: The Fabry-Perot Interferometer (FPI) on Dynamics Explorer is a remote sensing instrument designed to measure the temperature, meridional wind and density of the metastable atoms O(1S) and O(1D), and the ion O(plus)(2P) in the thermosphere. The measurements are made with a stable, high resolution Fabry-Perot etalon, which performs a wavelength analysis on the light detected from the thermospheric emission features by spatially scanning the interference fringe plane with a multichannel array detector. The wavelength analysis characterizes the Doppler line profile of the emitting species. A sequential altitude scan, performed by a commandable horizon scan mirror, provides a cross-sectional view of the thermodynamic and dynamic state of the thermosphere below the orbit of the Dynamics Explorer B satellite.

Optical fiber interferometers with [3×3] directional couplers: Analysis

Abstract: All‐guided wave interferometers using [3×3] directional couplers as beam splitters are analyzed in detail The characteristics of such interferometers are compared with those of conventional interferometers using [2×2] beam splitters It is shown that there are advantages in using [3×3] couplers instead of [2×2] couplers in the Mach‐Zehnder interferometric sensors and the Sagnac rotation sensors (gyroscopes)

Electron interferometry and interference electron microscopy

Abstract: A state-of-the-art review of electron interferometry and interference electron microscopy is given. The various types of interferometry device, interferometers and interference microscopes, which have been proposed and/or constructed are reviewed and commented upon. The electron biprism, by far the most successful interferometry device, is treated in some detail from both the experimental and theoretical (geometric and wave optics) points of view. The applications of electron interferometry are presented with particular reference to off-axis electron holography. Finally the future perspectives are indicated.

Chromatic dispersion measurement by white-light interferometry on metre-length single-mode optical fibres

Abstract: Chromatic dispersion near 08 ?m in a short (~1 m) single-mode optical fibre is determined by a white-light interferometric technique In particular, the wavelength-dependent group delay of the fibre is obtained directly from the spectra of the output light from a Mach-Zehnder interferometer illuminated by a GaAlAs LED Its application in single-mode fibre studies in the 13 ?m wavelength region is discussed

Semiconductor laser noise in an interferometer system

Abstract: The noise of semiconductor laser light after passing a Michelson interferometer has been measured for gain guided as well as index guided double-heterostructure injection lasers. This noise is mainly due to the partition noise and the frequency noise of the laser emission. Unless the interferometer is perfectly balanced, the observed noise is several orders of magnitude larger than the usual intensity noise of semiconductor lasers.

Accurate laser wavelength measurement with a precision two-beam scanning Michelson interferometer

Abstract: This paper gives the details of a precision two-beam scanning Michelson interferometer, designed and perfected for accurate comparison of an unknown laser wavelength and the precisely calibrated wavelength of a reference laser. An iodine Lamb-dip stabilized He–Ne 633-nm laser (calibrated with respect to a Kr standard) is used as the reference. The design incorporates features to minimize instrumental errors and the effect of fringe shifts caused by diffraction (in the IR). It is applied to accurate measurements of a stable CO2 laser wavelength tuned to the centers of its various transitions. Measurements are done by simultaneous fringe counting and relative fringe-phase comparison at the two wavelengths using on-line data storage and processing with an electronic digital computer. The accuracy in the 10-μm region is several parts in 109 and is limited by correction for diffraction fringe shifts. Because of its low-Q and broadband operating characteristics, it can be applied to rapid accurate laser wavelength measurements over the entire wavelength range permitted by its transmitting optics. In the visible range where the diffraction correction is small, the interferometer can be used to perform measurements to within several parts in 1011. The paper gives theoretical derivation of various diffraction corrections, the design and construction of the interferometer, the alignment procedures, detailed analysis of various error sources, and data processing. It also gives the details of a previously reported accurate measurement of the speed of light using the measured wavelength of the CO2R(14) line and its known frequency.

Phase noise of single-mode diode lasers in interferometer systems

Abstract: Measurements have been made of the phase noise of six different types of single‐mode diode laser in an unbalanced Michelson interferometer, as a function of optical path difference. The frequency dependence of the phase noise has also been determined. Possible origins of the frequency fluctuations which result in the phase noise are discussed. The detrimental effect of the phase noise on the sensitivity and dynamic range of optical fiber interferometer sensors is briefly discussed.

Photo-displacement imaging

Abstract: A modulated laser beam, incident on a surface, gives rise to a time-varying surface displacement. This displacement can be detected by means of a laser interferometer, thereby forming the basis for a novel imaging system. Preliminary results to demonstrate the viability of such a technique are presented.

A sensitive fiber-optic Fabry-Perot interferometer

Abstract: A Fabry-Perot interferometric sensor utilizing a single-mode optical fiber has been demonstrated, exhibiting a finesse of 18 and a sensitivity to phase modulation of 7.9 \times 10^{-7} rad/ \sqrt{Hz} at 1 kHz.

Thermal expansion reference data: silicon 300-850 K

Abstract: Measurements of the coefficient of linear thermal expansion of pure polycrystalline silicon were made with a polarization interferometer and a platinum resistance thermometer with an estimated error of less than 0.01 × 10-6 K-1.

Self calibrating contour measuring system using fringe counting interferometers

Abstract: A measuring arrangement is disclosed for measuring the contour of a two or three dimensional surface in which a redundant configuration of distance measuring systems is positioned above the surface being measured. Each distance measuring system monitors distance measurements to a point proximate the surface as the measuring point is moved across the surface. The distance measurements are taken from a sufficient number of points on the surface such that a sufficient quantity of data is obtained to define the system geometry and also to define the position of each measurement point. The data is transformed by recognized mathematical techniques into the coordinate positions of all of the measured points on the surface. In one embodiment for measuring the contour of a three dimensional surface, a tetrahedral arrangement of four distance measuring interferometers includes three interferometers positioned in a planar array above the measured surface and a fourth interferometer positioned at a central apex thereof. A retroreflector is placed adjacent to the measured surface to define the measuring point, and is selectively movable across the measured surface. A tetrahedral truss is positioned above the measured surface, and each interferometer has a beam steering head at one corner of the truss to aim the interferometer beam at the retroreflector during movements thereof. Each interferometer further includes a servo control system for controlling the beam steering head to maintain the interferometer beam aimed at the retroreflector.

Coherence limits for very-long-baseline interferometry

Abstract: The quality of the frequency standards used in very-long-baseline interferometry limits the coherent integration time and the accuracy of geodetic experiments except in special cases when clock instabilities can be made to cancel out by using differential interferometry. Formulas are derived for estimating the coherence of these interferometers from the Allan variances of the frequency standards. Experiments using extremely high-quality frequency standards, such as hydrogen masers, may be limited by the phase noise that results from atmospheric and ionospheric fluctuations.

Proposed optical test of metric gravitation theories

Abstract: An optical test of the metric theories of gravitation which employs a ring laser interferometer in an earthbound laboratory is suggested and analyzed. The proposed test would be sensitive to the presence of a preferred frame of the universe and to the geodetic and Lense-Thirring (frame-dragging) rotations of the local inertial frames relative to fixed stars. The frequency difference of the counterpropagating beams in a Sagnac-type experiment is determined within the framework of the parametrized post-Newtonian formalism. The precision with which the various parameters involved in the expression for the frequency difference can be measured is discussed.

Simple circuit for feedback stabilization of a single­ mode optical fiber interferometer

Abstract: Single‐mode optical fiber interferometers used with fiber hydrophones and other types of fiber sensors must be feedback stabilized to achieve maximum sensitivity and linearity in the presence of differential phase drift in their arms resulting from temperature fluctuations and other types of disturbances. A simple and effective electronic circuit for stabilizing such interferometers is described. The bandwidth of the feedback loop is 5 kHz, sufficiently wide to include information signals in addition to the drift correction signals. A high pass filter is used to remove the drift correction signals from the information signals.

Absolute distance measurements by variable wavelength interferometry.

Abstract: This paper describes a laser interferometer which provides absolute distance measurements using tunable lasers. An active feedback loop system, in which the laser frequency is locked to the optical path length difference of the interferometer, is used to tune the laser wavelengths. If the two wavelengths are very close, electronic frequency counters can be used to measure the beat frequency between the two laser frequencies and thus to determine the optical path difference between the two legs of the interferometer.

Method for the measurement of lengths and displacements

Abstract: A method and apparatus are provided for the remote measurement of a quantity of length or displacement, employing fiber-optical signal transmission between two or more interferometers, one of which acts as an optical transducer while the other acts as the receiver for the information about the quantity to be measured. A major advantage of the arrangement is that it operates with low-power, spatially incoherent broad-bandwidth light. More particularly, the quantity to be measured is represented by the path difference of two partial light beams passing through the arms of one interferometer, thus encoding the information about the path difference onto the light-flux resulting from the recombination of the two partial light beams. The transmitting interferometer is connected by an optical fiber with a receiving interferometer, where the information is recovered by evaluating the autocorrelation signal of the transmitted light. This use of optical fiber for connecting the two interferometers is another important feature which permits long distances to exist between the interferometers so that the measurement can be made of a quantity which is quite far away from the desired point of evaluation.

Measuring Microvibrations by Heterodyne Speckle Interferometry

Abstract: In-plane as well as out-of-plane displacements and vibrations of objects with diffusely scattering surfaces are measured in real time. Microvibrations with amplitudes down to 1 nm and frequencies up to 5 MHz were analyzed at a spatial resolution of 35 μm.

Intensity correlation metrology: A comparative study

Abstract: The statistical theory of fully developed, coherent speckle patterns is compared to classical coherence theory. It is shown that speckle correlations are directly analogous to the Hanbury Brown and Twiss effect. On that background a unified description is given for a number of measurement techniques based on intensity correlation measurements in scattered laser light: holographic interferometry, speckle pattern interferometry, speckle photography, stellar speckle interferometry, laser Doppler velocimetry and intensity correlation spectroscopy.

Fiber optical magnetic field sensor using magnetostrictive material

Abstract: A sensing element of magnetostrictive material associated with an optical fiber of an interferometer arm defining apparatus for detecting magnetic fields. The magnetostrictive material is adhered in close co-extensive adjacency with the optical fiber and in the presence of a magnetic field undergoes responsive longitudinal dimension changes which strains the optical fiber and induces a strain related phase shift in an optically propagating beam in the fiber detectable by interferometry.

Reflective surface analysis using moiré deflectometry.

Abstract: O. Kafri and A. Livnat Nuclear Research Centre-Negev, P.O. Box 9001, Beer Sheva, Israel. Received 19 March 1981. 0003-6935/81/183098-03$00.50. © 1981 Optical Society of America. In a previous publication, a method for phase object analysis was suggested. The method, moiré deflectometry (MD), is analogous to Mach-Zehnder interferometry. In this method, a distorted Ronchi ruling interferes with another

Tandem multipass Fabry-Perot interferometer for Brillouin scattering.

Abstract: A new design of a plane mirror Fabry-Perot interferometer with the mirror blanks freely supported by horizontal rings is described. Special attention is paid to the surface flatness and dielectric coatings of the mirrors. It is shown that any two piezoelectrically scanned Fabry-Perot interferometers can be synchronized in tandem operation using simple optics and standard electronic driving and stabilization equipment. Applications of the tandem system to Brillouin scattering are given. The observation of Brillouin spectra of supported thin plastic films and of a clamped metal surface is reported.