Multiple Interferometer Research Articles

Status of the search for gravitational wave bursts with the LIGO detectors

The LIGO Scientific Collaboration has been preparing for the search for burst-like events in the first LIGO science data. We present an overview of the goals of the burst search and provide a description of the different methods used to generate triggers from the raw time series. We also introduce the infrastructure of the prototype burst analysis pipeline. This brings together triggers from the gravitational wave and diagnostics channels in a statistically defined veto strategy, and then uses a multiple interferometer coincidence mechanism to identify candidate burst events. Finally, we discuss various aspects of the burst analysis, such as the identification of the detector stationarity and strategies in the determination of the background, upper limits and efficiency estimation. These are presented as of the time of the 7th GWDAW workshop that took place in Kyoto, Japan in December 2002.

A multiple beam interferometer for Bose‐Einstein condensates

AbstractWe condense 87Rb atoms in the combined potential of an optical standing wave superimposed on a harmonic magnetic trap. By releasing the atoms from the combined trap we realise a multiple beam atom interferometer. The measured atomic interferogram provides information about macroscopic coherence throughout the sample. The atomic distribution is characterised by interference peaks. The time evolution of the peaks, their relative population, as well as their radial size are in agreement with the predictions of theory. By a perturbation of the magnetic trap we induce an oscillating atomic current related to coherent tunnelling of the Bose‐Einstein condensates through the optical barriers. The frequency and amplitude of the oscillations are in agreement with a model based on the Josephson current‐phase relations.

A coordination architecture for spacecraft formation control

This paper addresses the problem of coordinating multiple spacecraft to fly in tightly controlled formations. The main contribution of the paper is to introduce a coordination architecture that subsumes leader-following, behavioral, and virtual-structure approaches to the multiagent coordination problem. The architecture is illustrated through a detailed application of the ideas to the problem of synthesizing a multiple spacecraft interferometer in deep space.

Optical chip immunoassay for hCG in human whole blood

We report on the development of an integrated optic chip sensor for performing rapid and sensitive immunoassays with human whole blood using human chorionic gonadotropin (hCG) as the model system. The optical chip is based on the Hartman interferometer, which uses a single planar lightbeam to address multiple interferometers, each comprising a signal/reference pair of sensing regions. The binding of antigen to specific capture antibodies on the signal sensing region causes a change in the refractive index of the surface layer, which is detectable by its effect on the evanescent field of the guided lightbeam. The reference-sensing region is coated with an irrelevant antibody, which optically cancels a large fraction of the non-specific adsorption that occurs on the specific-sensing region when the sensor is tested with clinical specimens. This work extends previous experiments with buffer and human serum to measurements in undiluted whole human blood. Optical chips were stored dry after surface functionalization, and rehydrated with blood. Colloidal gold nanoparticles conjugated to a second anti-hCG monoclonal antibody were used to provide signal amplification, thereby enhancing assay sensitivity, in a one-step procedure with the gold conjugate added to the test sample immediately prior to measurement. Background signals due to non-specific binding (NSB) in blood were found to be higher than those previously reported with human serum. In addition, a high level of background signal was found with the gold conjugate, which had not been observed in experiments with either buffer or serum. Nevertheless, hCG could be detected at 0.5 ng/ml within 10 min of sample application. The sensor response was linear over the concentration range 0.5–5 ng/ml hCG, as compared with the clinically-relevant range 0.3–1.5 ng/ml. Detection at higher concentrations was affected by scattering from large amounts of bound gold nanoparticles. However, initial binding rate measurements could be used to maintain assay quantitation.

Atomic spatial coherence monitoring and engineering with magnetic fields

We report on a simple and versatile method by which to measure and tailor massive particle ensemble coherences using pulsed magnetic fields. A multiple wave atom interferometer is demonstrated that uses a spin-echo procedure associated with the spatial separation of the Zeeman sublevel wave packets induced by magnetic forces. This scheme provides a means to determine ultralow temperatures by measuring the sample coherence length. Furthermore, we show how a pulsed quasiparabolic magnetic potential can be used to enhance the atom ensemble coherence length by a factor of 2.

Gauge Block Measurement Using a Wavelength Scanning Interferometer

A gauge block measurement system that uses a wavelength scanning interferometer was developed. By using a wavelength scanning technique, we determined the integer part of the interference fringe order. From that integer part, we determined the absolute length of a gauge block using only a single light source (wavelength scanning laser diode), even when no information on the nominal length of the gauge block was available. Using the Fourier transform technique to analyze the interference fringe, we measured the excess fraction parts of the interference fringe order with a resolution of over 0.003, and then we determined the integer part of the fringe order in the test measurement of a 10 mm gauge block. It was estimated that we could determine the integer part when the nominal length was shorter than approximately 100 mm, which can be expanded by improving the frequency stability of the light source. The final uncertainty was similar to that obtained with a conventional system based on a multiple wavelength interferometer.

Multiple-reflection interferometer for high accuracy measurement of small vibration displacement

A novel multiple-reflection interferometer is developed for the accurate measurement of sinusoidal vibration amplitudes, and its characteristics are analyzed theoretically and experimentally. The multiple-reflection system employs a right-angle prism and a convex lens, which is located in the probe beam path of a Michelson interferometer. The performance of the multiple reflection interferometer as a function of reflection number was assessed at the vibration frequency of 1250 Hz using Bessel function null method.

Position magnifying sensor

This paper describes the application of multiple beam shearing interferometry to a position magnifying sensor. A multiple beam shearing interferometer (MBSI) with a shear plate wedged in the vertical direction produces sharp multiple beam fringes. When the lateral displacement of a point source (which gives rise to the input beam of the MBSI) or its image occurs in the horizontal direction, these fringes move vertically in a magnified manner. This characteristic was used in a position magnifying sensor to detect the displacement of a point image. The advantages of the sensor include a large displacement magnification (more than a hundred times) and a large working distance.

Multiple beam atom interferometer: theory and experiment

We first give a detailed account of the theory of atom interferometers based on a sequence of laser pulses pro- jecting the atomic wave packets onto a spatially separating dark superposition state. We then describe the experimen- tal realization of a multiple beam atom interferometer based on this method. In our experiment, we observe an interfer- ence signal that shows the sharply peaked Airy-function like pattern characteristic for multiple beam interference. Besides this fringe sharpening effect, we observe a further significant difference compared to the signal of a conventional two-beam atom interferometer. When the time between the beamsplit- ting pulses is varied, we observe collapse and revival of the fringe pattern, which is caused by a recoil phase shift increas- ing quadratically with the transverse atomic momentum.

Plasma mass density, species mix, and fluctuation diagnostics using a fast Alfvén wave

We propose use of a fast Alfvén wave interferometer and reflectometer as a tokamak diagnostic to measure the plasma mass density, D–T species mix profile, and density fluctuations. Utilizing the property that the phase velocity of the fast wave propagating across the magnetic field is the Alfvén speed with thermal correction, this fast wave interferometer on the DIII-D tokamak was successfully used to obtain the line integrated density. Since the position of the ion–ion hybrid cutoff in tokamaks is uniquely determined by the species mix ratio and wave frequency, the reflectometer arrangement finds the species mix profile. The inversion method of reflectometry is discussed. The multiple chord interferometer also measures the mass density fluctuation profile.

A multiple white light interferometer

A multiple interferometer using the short coherence length of white light has been constructed and its operation demonstrated. With this apparatus, it is possible to count the number of light reflections between two parallel mirrors. The shift in fringe position resulting from differences in the optical thickness is proportional to the number of reflections between the two mirrors, enabling the resolution and measurement of a step difference of the order of 20 Å. This technique inherently has higher resolution than Michelson interferometers. As compared with Fabry–Perot interferometers, it offers an independent determination of the density of fringes, and has lower sensitivity to errors in minor parallelism. Further, the method does not require the extreme closeness in mirror spacing as compared to the Tolansky interferometer.

Visible wavelength Doppler lidar for measurement of wind and aerosol profiles during day and night

An incoherent (direct detection) Doppler lidar is developed that operates in the middle of the visible spectrum and measures wind and aerosol profiles during the day and night from the planetary boundary layer to the lower stratosphere. The primary challenge of making a lidar measurement in the visible spectrum during daylight hours is the strong presence of background light from the sun. To make a measurement of this type, the laser line must be isolated spectrally to the greatest extent possible. This has been accomplished through the use of a multiple etalon Fabry-Perot interferometer in combination with a narrow-band filter. The incoherent technique and system are a modified version of the Fabry-Perot interlerometer and image-plane detector technology developed for an earlier Doppler lidar developed at the University of Michigan and for the High-Resolution Doppler Imager (HRDI) now flying on the Upper Atmosphere Research Satellite. The incoherent Doppler analysis is discussed and sample measurements are shown. Winds are measured in the boundary layer with 100-m vertical resolution and 5-mm temporal resolution with 1 to 3 m s-1 accuracy.

Fibre-optic weigh-in-motion sensor

This paper presents a fibre-optic sensor to measure weight in motion based on a multiple fibre-optic interferometer. The differential phase between the arms of the interferometer produced by the pressure is compensated by a feedback system, thus converting pressure into voltage. This sensor can be used to separate the induced phase changes produced by two measurands acting simultaneously on the sensing arm. Results are presented that show the linearity of the detection scheme.

Wavelength-dependent sensitivity limitations affecting low light level Michelson stellar interferometry

The use of multiple aperture ground interferometers to measure directly the diameters of resolvable stars or to determine the separations and position angles of compact multiple star systems is well established in the literature. The general utility of this technique for producing catalogs of such observations, however, is fundamentally constrained by such noise processes as shot noise, detector dark current, and background radiation, all of which limit interferometric sensitivity. We review the various sensitivity limitations affecting low light level Michelson amplitude interferometry for these applications and calculate the wavelength-dependent detection thresholds as expressed in limiting stellar visual magnitudes that can be so achieved.

A unique machine for grinding large, off-axis optical components: the OAGM 2500

Design trends in the large optics field have progressed towards systems incorporating large, off-axis aspheric optical elements. These segments may be used in groups to form a single large parent optical surface. Segmented systems are necessary when the mirror size requirements exceed the capacity to produce a monolithic mirror blank. Segmented mirrors also have applications in space, where it is possible to launch a folded mirror array which can be deployed to provide a reflector larger than the diameter of the launch vehicle. The OAGM 2500 has been designed by Cranfield Precision Engineering to generate and measure off-axis elements prior to final polishing. This machine, together with a Neutral Ion Beam Figuring System, will provide Eastman Kodak Company with processes which are highly deterministic yielding rapid, cost efficient fabrication of large complex optical components. The resulting design has led to the manufacture of a machine weighing 130 tons, with a component capacity of 2.5 m × 2.5 m × 0.6 m and overall dimensions 8 m × 6 m × 5 m . Advanced three-axis CNC control for grinding and in situ metrology combined with a multiple path laser interferometer system and metrology frame, is incorporated to achieve the required component accuracy.

The Design and Manufacture of a Large CNC Grinding Machine for Off-Axis Mirror Segments

The trend in the design of large optics is towards systems employing off-axis aspheric elements frequently employed in groups to form a single large parent optical surface. This gives the optical system designer more options to work with but as the off-axis elements are not suitable for manufacture by classical methods of optical fabrication, creates the need for advanced methods of manufacture. To meet this requirement Cranfield Precision Engineering Ltd. have designed and are at an advanced stage of manufacture of a large three axis CNC machine for grinding and in-situ metrology of optical elements. Machine capacity is 2.5 m × 2.5 m × 0.61 m resulting in a machine of overall dimensions 8 m × 6 m × 5 m and overall weight 130 tonnes. Overall accuracy performance is achieved by use of an unusual metrology frame concept combined with a multiple path laser interferometer system of 2.5 nanometer resolution.

Ultra-high sensitivity accelerometers and gyroscopes using neutral atom matter-wave interferometry

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.

Measurement of the differential thermal expansion and temperature dependence of refractive index in gradient-index glass

The thermal expansion and temperature dependence of the refractive index in gradient-index glass have been investigated. In an earlier paper [ P. O. McLaughlin D. T. Moore , “ Models for the Thermal Expansion Coefficient and Temperature Coefficient of the Refractive Index in Gradient Index Glass,” Appl. Opt.24, this issue ( 15Dec.1985)] these two thermal properties were modeled as functions of the local glass composition within the gradient-index region. In this paper measurements of αL and dn/dT are described. A modified multiple Fabry-Perot interferometer was designed and built into an environmental temperature chamber to measure these thermal properties in gradient-index glass in the 0–100°C range. The interferometer operated under computer control to measure optically the differential thermal expansion and change in refractive-index profile in several samples of gradient-index glass.

Nonlinear optical phenomena in a multiple interferometer

A multiple interferometer is proposed and stimulated Raman radiation, stimulated Mandel’stam–Brillouin radiation, and Cerenkov-type optical parametric oscillation are considered in this interferometer, which is excited by an external light beam. An extremely low threshold intensity of the exciting beam is noted. Optical bistability and hysteresis, self-pulsing of the radiation intensities, amplification of amplitude-phase deviations in the incident pumping beam, limitation of the intensity of the beam transmitted by the interferometer, and nonlinear reflection of the beam from the multiple interferometer are predicted and discussed. It is also noted that the threshold for generation of the second Stokes component of stimulated Raman radiation and stimulated Mandel’stam–Brillouin radiation under the conditions discussed is usually not achieved, even for high excess of the exciting beam intensity over the threshold for generation of the first Stokes component.

High-resolution optical measurements of atmospheric winds from space 1: Lower atmosphere molecular absorption

The brightness spectrum of light scattered by the earth's atmosphere in the vicinity of molecular rotational lines is investigated. These absorption features are shown to be Doppler shifted by horizontal atmospheric winds. It is demonstrated that a modest aperture multiple etalon Febry-Perot interferometer can be used to monitor the global wind system from space by observing these Doppler shifts.