Showing papers on "Interferometry published in 1994"

The wavenumber shift in SAR interferometry

Abstract: SAR surveys from separate passes show relative shifts of the ground wavenumber spectra that depend on the local slope and the off-nadir angle. The authors discuss the exploitation of this spectral shift for different applications: 1) generation of "low noise" interferograms benefiting phase unwrapping, 2) generation of quick-look interferograms, 3) decorrelation reduction by means of tunable SAR systems (TINSAR), 4) range resolution enhancement, and 5) the combination of SAR data gathered by different platforms (airborne and satellite) for a "long-time coherence" study. >

Fundamentals of interferometric gravitational wave detectors

Abstract: The search for gravitational waves the nature of gravitational waves sources of gravitational waves linear systems, signals and noise optical readout noise folded interferometer arms thermal noise seismic noise and vibration isolation design of large interferometers null instruments feedback control systems an interferometer as an active null instrument resonant mass gravitational wave detectors detecting gravitational wave signals gravitational wave astronomy prospects

Direct phase determination in hologram interferometry with use of digitally recorded holograms

Abstract: A new method of phase determination in hologram interferometry is described. The Fresnel holograms, which represent the undeformed and the deformed states of the object, are generated on a CCD target and stored electronically. No lens or other imaging device is used. The reconstruction is done from the digitally stored holograms with mathematical methods. It is shown that the intensity as well as the phase can be calculated from the digitally sampled holograms. A comparison of the phases of the undeformed and the deformed states permits direct determination of the interference phase.

High-speed noncontact profiler based on scanning white-light interferometry

Abstract: We describe a system for fast three-dimensional profilometry, of both optically smooth and optically rough surfaces, based on scanning white-light techniques. The system utilizes an efficient algorithm to extract and save only the region of interference, substantially reducing both the acquisition and the analysis times. Rough and discontinuous surfaces can be profiled without the phase-ambiguity problems associated with conventional phase-shifting techniques. The system measures steps to 100 μm, scans a 10-μm range in 5 s, and has a smooth surface repeatability of 0.5 nm.

Theory of two-photon entanglement in type-II optical parametric down-conversion.

Abstract: The theory of the two-photon state generated by type-II optical parametric down-conversion is studied with emphasis on the space-time and polarization entanglement of the photons. Several experiments are reviewed that demonstrate various aspects of the quantum nature of this state. The theory of a different type of two-photon interferometer is presented.

On the derivation of coseismic displacement fields using differential radar interferometry: The Landers earthquake

Abstract: Presents a map of the coseismic displacement field resulting from the Landers, CA, June 28, 1992 earthquake derived using data acquired from an orbiting high resolution radar system. Data from the ERS-1 synthetic aperture radar instrument acquired in April, July, and August 1992 are used to generate a high resolution, wide area map of the displacements. The data represent the motion in the direction of the radar line of sight to cm level precision of each 30 m resolution element in a 113 by 00 km image. The coseismic displacement contour map gives a lobed pattern consistent with theoretical models of the displacement field from the earthquake. Comparison of these data with GPS and EDM survey data yield a correlation of 0.06, thus the radar measurements are a means to extend the point measurements acquired by traditional techniques to an area map format. The technique used is i) more automatic, ii) more precise, and iii) better validated than previous similar applications of differential radar interferometry. Since only remotely-sensed satellite data are required with no additional requirements for ancillary information, the technique is well suited for global seismic monitoring and analysis. >

Fiber end face interferometer

Abstract: PURPOSE:To measure the degree of eccentricity, radius of curvature, and amount of recess of a spherical surface of a ferrule edge by automatically measuring the degree of curvature of interference fringes and the center point of an optical fiber end face on an image memory. CONSTITUTION:Beams of a laser 1 pass through a diffusion lens 2, a beam splitter 4, and a collimater 5 and become parallel rays, pass a plane primary standard 6, and then are applied to a ferrule polished spherical surface 7. The reflection light of the spherical surface 7 forms interference fringes with that of the primary standard 6, is converted to the image of a CCD camera 10 via an image-forming lens 9, and is written into the image memory of a personal computer 12 and is displayed on a monitor 11, thus specifying measurement coordinates with a cursor. The distance between the primary standard 6 and the spherical surface 7 is calculated from a relation equation and then the degree of eccentricity of the spherical surface 7 is measured by reading the center coordinates between the interference pattern and the optical fiber using a personal computer 12, a radius of curvature is measured by the spacing between fringes, and the amount of recess is measured by changing the degree of curvature of interference fringes within the end face of an optical fiber 8 similarly.

Stabilizing unstable periodic orbits in fast dynamical systems.

Abstract: We present a technique for stabilizing unstable periodic orbits in low-dimensional dynamical systems that allows for control over a large domain of parameters. The technique uses a continuous feedback loop incorporating information from many previous states of the system in a form closely related to the amplitude of light reflected from a Fabry-P\'erot interferometer. We demonstrate that the approach is well suited for pratical implementation in fast systems by stabilizing a chaotic diode resonator driven at 10.1 MHz.

Automatic alignment of optical interferometers

Abstract: We present a description of a system for automatic alignment of optical interferometers. The technique relies on using differential phase modulation to permit the detection of the phase difference between two fundamental-mode Gaussian beams at the output of an interferometer. Measurements of the spatially varying phase difference between the two beams by use of one or more multielement photodiodes permits information to be derived about the mismatch in overlap between the phase fronts at the output of the interferometer.

The Feynman path integral approach to atomic interferometry: A tutorial

Abstract: Many problems of current interest in atomic interferometry lend themselves to a path integral treatment. We present a practical guide to solving such problems, taking as examples the gravitational experiments of Kasevich and Chu, and the atomic equivalents of the Sagnac and Aharonov-Bohm effects. Atomic interferometry is a new and rapidly-developing field of research, concerned with physical phenomena in which the wave-nature of neutral atoms plays an important role ill. The wide variety of internal degrees of freedom of an atom opens up new possibilities for investigation which do not exist in the more traditional types of interferometry using photons, electrons and neutrons. The development of atomic interferometry has been aided by recent technical advances, particularly in the manipulation of atoms. New mechanisms for slowing, deflecting, cooling and trapping atoms allow control of both their position and momentum. Also important has been the birth of "atomic optics", a range of mechanisms providing the equivalent of mirrors, beamsplitters and lenses for atoms. Recently it has been pointed out that certain high-resolution spectroscopy techniques which avoid the Doppler effect amount to realizing an atomic interferometer (2). These methods have since been adapted to measure inertial fields (due to rotation and gravitation) by atomic interferometry. The situation encountered in atomic interferometry experiments is often close to the classical limit. When this is the case a path integral approach to the analysis is very appropriate since it reduces to a calculation of integrals along classical paths. Further simplifications can be made if the Lagrangian is quadratic, as is true for a particle in a gravitational field or a rotating (*) The Laboratoire Kastler Brossel is associated with the CNRS and the Universit4 Pierre et Marie

Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources

Abstract: Experimental and theoretical investigations of coherent optical-frequency-domain reflectometry using semiconductor laser sources are presented. Good agreement was found between the analysis of the signal-to-noise ratio due to the phase noise and the experimental results. The sensitivity limit due to the quantum noise is also described. Limitations due to the nonlinearity in the optical frequency sweep produced by the thermal-response time of the laser and mode hopping are investigated and compared with experimental results. Two interferometric methods to characterize the thermal-response time of the laser and their implementations are described. The effects of mode hopping in the optical-frequency sweep are compared to numerical simulations. A simple formula to predict the position of spurious peaks due to mode hopping are presented. A spatial resolution of 400 /spl mu/m over 10 cm was obtained by correcting the nonlinearity in the optical-frequency sweep by using an auxiliary interferometer. The Rayleigh backscattering was observed for the first time over more than 400 m of fiber using a DFB laser coupled to an external cavity. >

Surface micromachined tuneable interferometer array

Abstract: The development of compact light modulators integrated on the same chip as the signal processing opens many opportunities for combining inter-chip optical communications with standard silicon circuitry. The use of surface micromachining allows high speed of operation and small size integration with other circuitry. The optical and mechanical requirements for the devices also have to be considered, to ensure compatability with standard silicon processing. A surface micromachining process, using an oxide sacrificial layer and poly/nitride/poly membranes, has been developed. This paper presents the optical and mechanical considerations in the development of a compact micromachined silicon Fabry-Perot interferometer. Initial tests have shown that these micromachined membranes represent a compact and effective light modulating method.

Fourier-transform speckle profilometry: three-dimensional shape measurements of diffuse objects with large height steps and/or spatially isolated surfaces

Abstract: An interferometric technique for automated profilometry of diffuse objects has been proposed. It is based on the Fourier-fringe analysis of spatiotemporal specklegrams produced by a wavelength-shift interferometer with a laser diode as a frequency-tunable light source. Unlike conventional moire techniques the proposed technique permits the objects to have discontinuous height steps and/or surfaces spatially isolated from one another. Experimental results are presented that demonstrate the validity of the principle.

Spectroscopic imaging device employing imaging quality spectral filters

Abstract: Techniques for providing spectroscopic imaging integrates an acousto-optic tunable filter (AOTF), or an interferometer, and a focal plane array detector. In operation, wavelength selectivity is provided by the AOTF or the interferometer. A focal plane array detector is used as the imaging detector in both cases. Operation within the ultraviolet, visible, near-infrared (NIR) spectral regions, and into the infrared spectral region, is achieved. The techniques can be used in absorption spectroscopy and emission spectroscopy. Spectroscopic images with a spectral resolution of a few nanometers and a spatial resolution of about a micron, are collected rapidly using the AOTF. Higher spectral resolution images are recorded at lower speeds using the interferometer. The AOTF technique uses entirely solid-state components and requires no moving parts. Alternatively, the interferometer technique employs either a step-scan interferometer or a continuously modulated interferometer.

Maximum likelihood estimation for SAR interferometry

Abstract: Synthetic aperture radar (SAR) interferometry (InSAR) uses phase differences between overlapping SAR images to estimate terrain height and terrain height changes In addition, the coherence magnitude between the images is often used as a measure of the quality of the data and the processing By modeling the SAR image data as independent circular Gaussian random variates, the authors develop the maximum likelihood (ML) estimates for interferogram phase, coherence magnitude, and the variance of the underlying circular Gaussian distribution They show that the ML estimate of interferogram phase is equivalent to the standard technique of computing the phase of averaged complex returns The ML estimate of the coherence magnitude depends on the estimated interferogram phase In comparison, the sample coherence magnitude estimate based on amplitudes alone is badly biased They also derive the Cramer-Rao bound for each ML estimate The ML estimate of interferogram phase is close to this bound for moderate to high coherence values Similarly, the coherence magnitude is close to the bound for values of coherence greater than approximately 1/2 For coherence magnitudes less than 1/2, the ML estimate of coherence magnitude is biased for data samples sizes up to 16 samples >

Method and apparatus for surface topography measurement by spatial-frequency analysis of interferograms

Abstract: An optical system for measuring the topography of an object (3) includes an interferometer (1) with a multiple-color or white-light source (4), a mechanical scanning apparatus (13) for varying the optical path difference between the object and a reference surface, a two-dimensional detector array (9), and digital signal processing apparatus (2) for determining surface height from interference data. Interferograms for each of the detector image points in the field of view are generated simultaneously by scanning the object in a direction approximately perpendicular to the illuminated object surface while recording detector data in digital memory. These recorded interferograms for each image point are then transformed into the spatial frequency domain by Fourier analysis, and the surface height for each corresponding object surface point is obtained by examination of the complex phase as a function of spatial frequency. A complete three-dimensional image of the object surface is then constructed from the height data and corresponding image plane coordinates.

Measurement of large plane surface shapes by connecting small-aperture interferograms

Abstract: We propose a method to obtain the shape of a large plane surface by connecting phase distributions measured by a small-aperture interferometer. These separately measured phase distributions cannot be connected directly because the object will tilt or have vertical displacement during the measurements. To correct these errors, the measurements are made so that the adjacent interferograms have common areas, and these interferograms are connected to minimize the difference of the phase distributions in the common areas. A matrix equation is derived to obtain coefficients to correct tilt and vertical displacement, and the accuracy of connection increases in proportion to an exponent of 1.5 of the width of the common area.

Stepped-wavelength optical-fiber Bragg grating arrays fabricated in line on a draw tower

Abstract: More than 450 fiber Bragg gratings have been fabricated in line during the draw process in a period of 1 h with single pulses of a KrF excimer laser. Arrays of gratings have been written at different Bragg wavelengths by using an automated, computer-controlled interferometer.

Frequency-domain interferometer for measuring the phase and amplitude of a femtosecond pulse probing a laser-produced plasma.

Abstract: A frequency-domain interferometer for probing the variations of the dielectric constant of a plasma with sub-100- fs temporal resolution and lambda/2000 phase resolution is described. Imaging the plasma on the entrance slit of a spectrograph provides spatial resolution along a diameter of the focal spot. The technique is used to map out the expansion of the critical density surface of a femtosecond laser-produced plasma with subnanometer spatial resolution along the laser axis.

Reciprocal reflection interferometer for a fiber-optic Faraday current sensor

Abstract: A reciprocal fiber-optic reflection interferometer for remote measurement of electrical current through the Faraday effect is described. The effects of polarization cross coupling because of nonideal elements are eliminated with a low-coherence source. Nonreciprocal birefringence phase modulation is employed for detection of the Faraday phase shift. The theoretical predictions are confirmed by measurements with a piece of straight fiber as the sensing element in a 100-turn solenoid. Currents from 0 to 40 A have been measured with a linear response and a noise limit of ∼0.015A/Hz.

Detection of ultrasonic motion of a scattering surface by two‐wave mixing in a photorefractive GaAs crystal

Abstract: The performance of an interferometric system based on two‐wave mixing at 1.06 μm in undoped GaAs crystal, for the remote detection of transient motion of a scattering surface, is described. In this system, the wave scattered by the surface is mixed inside the photorefractive crystal with a pump wave directly derived from the laser to provide the reference wave of the interferometer. The system shows several features appropriate to industrial applications, although its sensitivity is less than passive interferometric systems of the confocal Fabry–Perot type presently in use, except in the low frequency range (below 1 MHz).

Mach-Zehnder interferometer polarization splitter in InGaAsP/InP

Abstract: A passive TE/TM mode polarization splitter based on a Mach-Zehnder interferometer is demonstrated. Insertion loss of 1.5 db and extinction ratios of /spl minus/19 dB for TE and /spl minus/15 dB for TM have been measured at 1510-nm wavelength. The device attains large optical bandwidth employing a pair of multimode interference (MMI) couplers and a wavelength-tolerant birefringent structure. >

``Sagnac'' effect: A century of Earth-rotated interferometers

Abstract: The earliest prediction of the Sagnac effect, and of the possibility of detecting the Earth’s rotation with an interferometer of square kilometer area, is by Lodge (1893, 1897). We illustrate the extraordinary range of theoretical motivations for the experimental study of the Sagnac effect, starting with previously unpublished correspondence between Lodge and Larmor, and ending with present (and planned) ring interferometer experiments whose sensitivity to the Earth’s rotation is of the order of parts per million (billion, respectively).

Diffraction efficiency analysis of a parallel-aligned nematic-liquid-crystal spatial light modulator.

Abstract: An optically addressed parallel-aligned nematic-liquid-crystal spatial light modulator is developed for applications in optical information processing and interferometry. Its performance, including diffraction efficiency, is measured, and a theoretical analysis of diffraction efficiency is performed. A comparison between the experimental results and the theoretical analysis shows good agreement. The diffraction efficiency of near-sinusoidal gratings written on the device is of the order of 30%, which is close to theoretical maximum.

Talbot-vonLau Atom Interferometry with Cold Slow Potassium

Abstract: A dc hot thermal and an ac-modulated cold slow potassium beam copropagate and pass through an atom de Broglie--wave interferometer, consisting of a sequence of three microfabricated diffraction gratings. Talbot-vonLau interference fringes are formed and sensed by measuring transmission with a hot wire as a function of grating position. The hot beam produces diffraction-limited shadow Moir\'e fringes, while the longer de Broglie wavelength slow beam produces interference fringes with high visibility at the fifth and sixth spatial harmonics of the shadow Moir\'e fringes.

Low-coherence deformation sensors for the monitoring of civil-engineering structures

Abstract: An optical-fiber deformation sensor with a resolution of 10 μm and an operational range of 60 mm has been realized. The system is based on low-coherence interferometry in standard single-mode telecommunication fibers. It allows the monitoring of large structures over several months without noticeable drift. No continuous measurement is needed and the system is insensitive to variations of the fiber losses. This technique has been applied to the monitoring of a 20 m × 5 m × 0.5 m, 120 ton concrete slab over six months. It is possible to measure the shrinkage of concrete and its elastic coefficient during pre-straining, giving reproducible results in good agreement with theoretical calculations and measurements performed on small concrete samples. This paper describes the optical arrangement and the procedures used to install optical fibers in concrete.

Atomic Interferometer Based on Adiabatic Population Transfer

Abstract: We demonstrate an atomic interferometer based on the transfer of population between two ground states via adiabatic following using a nonabsorbing "dark" superposition state. This type of interferometer promises to be useful for precise measurement of the photon recoil energy and also for large area atomic interferometers since it allows transfer of a large number of photon recoil momenta to the atoms with high efficiency. In preliminary experiments, we have obtained a coherent transfer efficiency of 95% with transfer of photon momenta and 98.4% with no transfer of momenta. Over 140 photon momenta have been transferred coherently to the atoms.

Experimental demonstration of an automatic alignment system for optical interferometers.

Abstract: An automatic alignment system, based on a differential phase-sensing technique described in a companion paper [Appl. Opt. 33, 0000, (1994)], has been experimentally demonstrated on the 10-m prototype laser interferometric gravitational wave detector in Glasgow. The alignment system developed was used to control the orientations of two mirrors in a 10-m-longsuspended Fabry–Perot cavity with respect to the direction defined by the input laser beam. The results of the test and a discussion of the performance of the system are given.

Digital recording and reconstruction of holograms in hologram interferometry and shearography

Abstract: The fundamentals of digital recording and mathematical reconstruction of Fresnel holograms are described. The object is recorded in two different states, and the holograms are stored electronically with a charge-coupled-device detector. In the process of reconstruction the digitally sampled holograms are applied to the different coherent optical methods as hologram interferometry and shearography. If the holograms are superimposed and reconstructed jointly, a holographic interferogram results. If a shearing is introduced in the reconstruction process, a shearogram results. This means that the evaluation technique, e.g., hologram interferometry or shearography, can be influenced by numerical methods.