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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Study on avalanche photodiode influence on heterodyne laser interferometer linearity

In the paper we analyze factors reducing the possible accuracy of the heterodyne laser interferometers. The analysis is performed for the avalanche-photodiode input stages but is in main points valid also for stages with other type of photodetectors. Instrumental error originating from optical, electronic and digital signal processing factors is taken into consideration. We stress factors which are critical and those which can be neglected at certain accuracy requirements. In the work we prove that it is possible to reduce errors of the laser instrument below 1 nm point for multiaxial APD based interferometers by precise control of incident optical power and the temperature of the photodiode.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Assessment of the beam path deflection for a vertically installed microwave interferometer in SUNIST

Microwave interferometry has been widely employed to provide reliable line averaged electron density measurement on plasma devices. For a vertically installed interferometer on a tokamak, the refraction problem, which distorts the beam path and aggravates power loss at the receiving antenna, may become significant if taking the cross section shape into account. Increasing the frequency of the probing microwave can alleviate the distortion, but at the expense of losing the density resolution. To seek for an optimized frequency, previous calculations are mainly based on the cylindrical column geometry which grossly underestimates the deflection of the beam path induced by the plasma shape, and empirical suggestions indicating n{sub e0}/n{sub c} = 1/2 ∼ 1/3 may not always be the appropriate option. Here a single ray tracing method is applied to estimate the final horizontal deviation at the receiving antenna, which is supposed to represent the level of power loss. The calculation is carried out under the real tokamak geometry in Sino-UNIted Spherical Tokamak (SUNIST) with the cross section parameters obtained from the equilibrium reconstruction, and the result indicates that for a target density of 1.2 × 10{sup 19} m{sup −3}, a frequency of at least 100 GHz is desirable to reduce the power loss to an acceptable level. This would be helpful for the design of a vertically installed interferometer on SUNIST.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

A 60-GHz interferometer with a local oscillator integrated antenna array for divertor simulation experiments on GAMMA 10/PDX

In conventional multichannel/imaging microwave diagnostics of interferometry, reflectometry, and electron cyclotron emission measurements, a local oscillator (LO) signal is commonly supplied to a receiver array via irradiation using LO optics. In this work, we present a 60-GHz interferometer with a new eight-channel receiver array, called a local oscillator integrated antenna array (LIA). An outstanding feature of LIA is that it incorporates a frequency quadrupler integrated circuit for LO supply to each channel. This enables simple and uniform LO supply to the receiver array using only a 15-GHz LO source and a coaxial cable transmission line instead of using an expensive 60-GHz source, LO optics, and a waveguide transmission line. The new interferometer system is first applied to measure electron line-averaged density inside the divertor simulation experimental module (D-module) on GAMMA 10/PDX tandem mirror device.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Selection of linear-cavity fibre laser radiation using a reflection interferometer

We consider the use of a two-mirror multibeam reflection interferometer as a selector of linear-cavity single-mode fibre laser radiation and present experimental data on continuous wavelength tuning of an erbium-doped fibre laser. Conditions are found for single-longitudinal-mode operation of the fibre laser cavity using a reflection interferometer, with the possibility of broadband wavelength tuning. (control of laser pulse parameters)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Noise power spectral density of a fibre scattered-light interferometer with a semiconductor laser source

Spectral characteristics of the noise intensity fluctuations at the output of a scattered-light interferometer, caused by phase fluctuations of semiconductor laser radiation are considered. This kind of noise is one of the main factors limiting sensitivity of interferometric sensors. For the first time, to our knowledge, the expression is obtained for the average noise power spectral density at the interferometer output versus the degree of a light source coherence and length of the scattering segment. Also, the approximate expressions are considered which determine the power spectral density in the low-frequency range (up to 200 kHz) and in the limiting case of extended scattering segments. The expression obtained for the noise power spectral density agrees with experimental normalised power spectra with a high accuracy. (interferometry of radiation)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Fabrication-tolerant integrated polarisation splitter based on cascaded Mach–Zehnder interferometers

We report a fabrication-tolerant polarisation splitter based on cascaded Mach – Zehnder interferometers. This configuration enables a factor of 2 – 3 increase (at the 20 dB level) in the tolerance to the phase difference in comparison with a single interferometer. As an example, we present numerical simulation of a splitter with a centre wavelength of 650 nm, based on a planar waveguide from Si{sub 3}N{sub 4}. The permissible channel waveguide width deviation from calculation results (20-dB extinction coefficient bandwidth) is ∼8% (∼30 nm) for the TE polarisation and ∼30% (100 nm) for the TM polarisation. (fiber and integrated optics)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

On the possibility of using the phase characteristic of a ring interferometer in microoptical gyroscopes

The prototype schemes of a microoptical gyroscope (MOG) developed to date on the basis of passive ring cavities imply the use of the amplitude characteristic only, since they operate using the dip in the transmission coefficient. We have analysed the possibility of creating a MOG, in which the phase characteristic is used as well. The phase characteristic of a ring interferometer has distinctive features in the vicinity of the cavity eigenfrequencies, which may be used to determine the angular velocity. A method for the angular velocity determination using both the phase and the amplitude characteristics of the interferometer is considered. (laser gyroscopes)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Control of the phase characteristics of Stokes waves in a Michelson interferometer with SBS mirrors

It is found that, when using stimulated Brillouin scattering (SBS) mirrors (mounted in a ring Michelson interferometer) with counterfocusing, under pumping by pulses with steep (2−3 ns) leading edges and applying Freon FC-75 as an active medium, the phase difference of the Stokes waves on the semitransparent interferometer mirror obeys the dependence Δφ=2ΔkΔl (Δk is the difference in the magnitudes of the pump and Stokes component wave vectors and Δl is the difference in the optical arm lengths). (paper)

42 ENGINEERING↗
DOE OSTI2018

Temperature evolution of interferometer visibility in a small radius fibre coil current sensor

We have experimentally demonstrated periodic oscillations of interferometer visibility in a current sensor in response to changes in the temperature of a small-radius spun fibre sensing coil. The observed effect has been shown to depend on the magnitude of the bend-induced linear birefringence in the spun fibre in the magnetically sensitive coil and the temperature behaviour of the built-in linear birefringence in the fibre. Using a model that considers a helical structure of the built-in linear birefringence axes in spun fibre, we have shown that the above factors result in periodic oscillations of the ellipticity of polarised light at the ends of the sensing coil and that this underlies the temperature oscillations of interferometer visibility in the current sensor. The effect may cause errors in the response of a fibre-optic current sensor with a small sensing coil. (fibre-optic sensors)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Method for manufacturing a fibre reflection interferometer based on a metal-dielectric diffraction structure

A new method for manufacturing a two-mirror reflection fibre interferometer in a single-mode fibre consisting of an input mirror with an asymmetric reflection coefficients and a highly reflective end mirror is presented and experimentally demonstrated. The input mirror is based on a metal-dielectric diffraction structure in the form of an aperture in an aluminium film and a dielectric multilayer coating, which provides asymmetry of the reflection coefficient. The method includes the calculation of the energy coefficients of the aluminium film with a hole, the determination of the optimal diameter of the hole, as well as making of the hole, the entrance mirror and the resonator with a short fibre base. A sample interferometer is demonstrated that has an increased (at least by two orders of magnitude) radiation resistance compared to variants based on a continuous metal film, namely, at least 100 mW of radiation in a single-mode SMF-28e fibre at a wavelength of 1550 nm. (fibre optics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Influence of birefringent fibre joints on the visibility drift in a Mach – Zehnder interferometer

It is shown that imperfect joints of linear birefringent fibres in a fibre interferometer may result in an uncontrolled visibility drift under varying environmental conditions even with a standard phase matching device. As an example, a double Mach – Zehnder interferometer is considered, which is employed in schemes of quantum key distribution. Results of numerical simulation demonstrate the standard deviation of the quantum bit error rate (QBER), which is comparable to an average QBER value. (paper)

36 MATERIALS SCIENCE↗
DOE OSTI2020

Three-colour digital holographic microscopy based on a Mach – Zender interferometer and a solid-state RGB laser

We have developed a facility for recording colour digital holograms involving a Mach – Zender interferometer and a pulsed solid-state RGB laser, which radiates simultaneously at three wavelengths: 451, 532, and 634 nm. These wavelengths are obtained in the conversion of the radiation of a pulsed Nd{sup 3+} : YAG laser (1064 nm), which operates in the regime of intracavity parametric oscillation at a wavelength of 1570 nm, with the subsequent conversion of its frequencies to the red, green, and blue spectral regions in nonlinear KTP-crystal elements. The combination of this three-wavelength pulsed light source with the Mach – Zender interferometer provides the simultaneous recording of three spectral digital holograms with one matrix RGB radiation detector. Pulsed three-colour digital holography shows promise for the analysis of fast processes and rapidly varying colour phase objects. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

PLATFORM DEFORMATION PHASE CORRECTION FOR THE AMiBA-13 COPLANAR INTERFEROMETER

We present a new way to solve the platform deformation problem of coplanar interferometers. The platform of a coplanar interferometer can be deformed due to driving forces and gravity. A deformed platform will induce extra components into the geometric delay of each baseline and change the phases of observed visibilities. The reconstructed images will also be diluted due to the errors of the phases. The platform deformations of The Yuan-Tseh Lee Array for Microwave Background Anisotropy (AMiBA) were modeled based on photogrammetry data with about 20 mount pointing positions. We then used the differential optical pointing error between two optical telescopes to fit the model parameters in the entire horizontal coordinate space. With the platform deformation model, we can predict the errors of the geometric phase delays due to platform deformation with a given azimuth and elevation of the targets and calibrators. After correcting the phases of the radio point sources in the AMiBA interferometric data, we recover 50%-70% flux loss due to phase errors. This allows us to restore more than 90% of a source flux. The method outlined in this work is not only applicable to the correction of deformation for other coplanar telescopes but also to single-dish telescopes with deformation problems. This work also forms the basis of the upcoming science results of AMiBA-13.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Measuring the cosmological 21 cm monopole with an interferometer

A measurement of the cosmological 21 cm signal remains a promising but as-of-yet unattained ambition of radio astronomy. A positive detection would provide direct observations of key unexplored epochs of our cosmic history, including the cosmic dark ages and reionization. In this paper, we concentrate on measurements of the spatial monopole of the 21 cm brightness temperature as a function of redshift (the “global signal”). Most global experiments to date have been single-element experiments. In this paper, we show how an interferometer can be designed to be sensitive to the monopole mode of the sky, thus providing an alternate approach to accessing the global signature. We provide simple rules of thumb for designing a global signal interferometer and use numerical simulations to show that a modest array of tightly packed antenna elements with moderately sized primary beams (FWHM of ∼40{sup ∘}) can compete with typical single-element experiments in their ability to constrain phenomenological parameters pertaining to reionization and the pre-reionization era. We also provide a general data analysis framework for extracting the global signal from interferometric measurements (with analysis of single-element experiments arising as a special case) and discuss trade-offs with various data analysis choices. Given that interferometric measurements are able to avoid a number of systematics inherent in single-element experiments, our results suggest that interferometry ought to be explored as a complementary way to probe the global signal.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Comparison of machine learning systems trained to detect Alfvén eigenmodes using the CO 2 interferometer on DIII-D

Abstract A Machine-Learning (ML) based detection scheme that automatically detects Alfvén Eigenmodes (AE) in a labelled DIII-D database is presented here. Controlling AEs is important for the success of planned burning plasma devices such as ITER, since resonant fast ions can drive AEs unstable and degrade the performance of the plasma or damage the first walls of the machine vessel. Artificial Intelligence could be useful for real-time detection and control of AEs in steady-state plasma scenarios by implementing ML-based models into control algorithms that drive actuators for mitigation of AE impacts. Thus, the objective is to compare differences in performance between using two different recurrent neural network systems (Reservoir Computing Network and Long Short Term Memory Network) and two different representations of the C O 2 phase data (simple and crosspower spectrograms). All C O 2 interferometer chords are used to train both models, but only one is processed during each training step. The results from the model and data comparison show higher performance for the RCN model (True Positive Rate = 90% and False Positive Rate = 14%), and that using simple magnitude spectrograms is sufficient to detect AEs. Also, the vertical C O 2 interferometer chord passing near the center is better for ML-based detection of AEs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

High energy x-ray phase contrast CT using glancing-angle grating interferometers

Purpose: The authors present initial progress toward a clinically compatible x-ray phase contrast CT system, using glancing-angle x-ray grating interferometry to provide high contrast soft tissue images at estimated by computer simulation dose levels comparable to conventional absorption based CT. Methods: DPC-CT scans of a joint phantom and of soft tissues were performed in order to answer several important questions from a clinical setup point of view. A comparison between high and low fringe visibility systems is presented. The standard phase stepping method was compared with sliding window interlaced scanning. Using estimated dose values obtained with a Monte-Carlo code the authors studied the dependence of the phase image contrast on exposure time and dose. Results: Using a glancing angle interferometer at high x-ray energy (∼45 keV mean value) in combination with a conventional x-ray tube the authors achieved fringe visibility values of nearly 50%, never reported before. High fringe visibility is shown to be an indispensable parameter for a potential clinical scanner. Sliding window interlaced scanning proved to have higher SNRs and CNRs in a region of interest and to also be a crucial part of a low dose CT system. DPC-CT images of a soft tissue phantom at exposures in the range typical for absorption based CT of musculoskeletal extremities were obtained. Assuming a human knee as the CT target, good soft tissue phase contrast could be obtained at an estimated absorbed dose level around 8 mGy, similar to conventional CT. Conclusions: DPC-CT with glancing-angle interferometers provides improved soft tissue contrast over absorption CT even at clinically compatible dose levels (estimated by a Monte-Carlo computer simulation). Further steps in image processing, data reconstruction, and spectral matching could make the technique fully clinically compatible. Nevertheless, due to its increased scan time and complexity the technique should be thought of not as replacing, but as complimentary to conventional CT, to be used in specific applications.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Measurement Error of Interferometers with Diffraction Reference Wave

An experimental setup and results on aberration of sources of a reference spherical wave (SRSW) based on a single-mode optical fiber with a subwavelength output aperture obtained with the aid of an optical part of recording system (OPRS) are presented. SRSW and OPRS are developed for referenceless interferometer with diffraction reference wave. Methods for minimization of the measurement error are proposed. The SRSW and OPRS provide subnanometer measurement accuracy for optics. An increase in the measurement accuracy of the interferometer to a picometer level is discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Testing a Model of Planck-Scale Quantum Geometry With Broadband Correlation of Colocated 40m Interferometers

The Holometer is designed to test for a Planck diffractive-scaling uncertainty in long-baseline position measurements due to an underlying noncommutative geometry normalized to relate Black hole entropy bounds of the Holographic principle to the now-finite number of position states. The experiment overlaps two independent 40 meter optical Michelson interferometers to detect the proposed uncertainty as a common broadband length fluctuation. 150 hours of instrument cross-correlation data are analyzed to test the prediction of a correlated noise magnitude of $7\times10^{−21}$ m/$\sqrt{\rm Hz}$ with an effective bandwidth of 750kHz. The interferometers each have a quantum-limited sensitivity of $2.5\times 10^{−18}$ m/$\sqrt{\rm Hz}$, but their correlation with a time-bandwidth product of $4\times 10^{11}$ digs between the noise floors in search for the covarying geometric jitter. The data presents an exclusion of 5 standard deviations for the tested model. This exclusion is defended through analysis of the calibration methods for the instrument as well as further sub shot noise characterization of the optical systems to limit spurious background-correlations from undermining the signal.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗