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NASA NTRS2000

Mid-Latitude Temperatures at 87 km: Results From Multi-Instrument Fourier Analysis

Using a novel Fourier fitting method we combine two years of mid-latitude temperature measurements at 87 km from the High Resolution Doppler Imager, the Colorado State University lidar, and the Peach Mountain Interferometer. After accounting for calibration bias, significant local-time variations on the order of 10 K were observed. Stationary planetary waves with amplitudes up to 10 K were observed during winter, with weaker wave amplitudes occurring during other seasons. Because of calibration biases among these instruments, we could estimate the annual mean temperature to no better than 193.5 plus or minus 8.5 K.

FOURIER ANALYSIS↗

NASA NTRS2004

Modeling the TPF interferometer

The Terrestrial Planet Finder interferometer design concepts are large and complex systems that must operate in environments that are impractical to reproduce in preflight testing. The structurally-connected design is 36 meters long - longer than all but one thermal vacuum chamber in existence. The formation flying design will be comprised of up to five separate spacecraft, each with a sunshield over 15 meters on a side, and is designed to operate with formation sizes spanning over 100 meters to very close formations. System-level verification of the performance of the designs will need to rely on analytical modeling. The effort to model the many physical aspects of the designs under study is under way*. This paper describes the program of modeling for the TPF-I concepts. The program includes a number of types of models, such as the standard stand-alone optics, thermal, and structural models, as well as an end-to-end performance model of the project system called the Observatory Simulation. Aspects of each model are discussed including the purpose, methods of implementation (software applications), and approaches to validation. Program-level considerations (such as model-to-model integration and configuration management) are also discussed. Given that there are at least seven different organizations contributing to model developments and more than twenty separate models, these are special challenges.

Henry, Curt↗

NASA NTRS2012

Telescope Alignment From Sparsely Sampled Wavefront Measurements Over Pupil Subapertures

Alignment of two-element telescopes is a classic problem. During recent integration and test of the Space Interferometry Mission s (SIM s) Astrometric Beam Combiner (ABC), the innovators were faced with aligning two such telescope subsystems in the presence of a further complication: only two small subapertures in each telescope s pupil were accessible for measuring the wavefront with a Fizeau interferometer. This meant that the familiar aberrations that might be interpreted to infer system misalignments could be viewed only over small sub-regions of the pupil, making them hard to recognize. Further, there was no contiguous surface of the pupil connecting these two subapertures, so relative phase piston information was lost; the underlying full-aperture aberrations therefore had an additional degree of ambiguity. The solution presented here is to recognize that, in the absence of phase piston, the Zygo measurements primarily provide phase tilt in the subaperture windows of interest. Because these windows are small and situated far from the center of the (inaccessible) unobscured full aperture, any aberrations that are higher-order than tilt will be extremely high-order on the full aperture, and so not necessary or helpful to the alignment. Knowledge of the telescope s optical prescription allows straightforward evaluation of sensitivities (subap mode strength per unit full-aperture aberration), and these can be used in a predictive matrix approach to move with assurance to an aligned state. The technique is novel in every operational way compared to the standard approach of alignment based on full-aperture aberrations or searching for best rms wavefront. This approach is closely grounded in the observable quantities most appropriate to the problem. It is also more intuitive than inverting full phase maps (or subaperture Zernike spectra) with a ray-tracing program, which must certainly work in principle, but in practice met with limited success. Even if such classical alignment techniques became practical, the techniques reported here form a reassuringly transparent and intuitive check on the course of the alignment with very little computational effort.

Bloemhof, Eric E.↗

NASA NTRS2003

Extraction of Profile Information from Cloud Contaminated Radiances

Clouds act to reduce the signal level and may produce noise dependence on the complexity of the cloud properties and the manner in which they are treated in the profile retrieval process. There are essentially three ways to extract profile information from cloud contaminated radiances: (1) cloud-clearing using spatially adjacent cloud contaminated radiance measurements, (2) retrieval based upon the assumption of opaque cloud conditions, and (3) retrieval or radiance assimilation using a physically correct cloud radiative transfer model which accounts for the absorption and scattering of the radiance observed. Cloud clearing extracts the radiance arising from the clear air portion of partly clouded fields of view permitting soundings to the surface or the assimilation of radiances as in the clear field of view case. However, the accuracy of the clear air radiance signal depends upon the cloud height and optical property uniformity across the two fields of view used in the cloud clearing process. The assumption of opaque clouds within the field of view permits relatively accurate profiles to be retrieved down to near cloud top levels, the accuracy near the cloud top level being dependent upon the actual microphysical properties of the cloud. The use of a physically correct cloud radiative transfer model enables accurate retrievals down to cloud top levels and below semi-transparent cloud layers (e.g., cirrus). It should also be possible to assimilate cloudy radiances directly into the model given a physically correct cloud radiative transfer model using geometric and microphysical cloud parameters retrieved from the radiance spectra as initial cloud variables in the radiance assimilation process. This presentation reviews the above three ways to extract profile information from cloud contaminated radiances. NPOESS Airborne Sounder Testbed-Interferometer radiance spectra and Aqua satellite AIRS radiance spectra are used to illustrate how cloudy radiances can be used in the profile retrieval process.

Smith, W. L.↗

NASA NTRS1985

Optical interferometry in fluid dynamics research

Optical interferometry techniques have been applied to the investigation of transonic airfoil flow fields in large-scale wind tunnels. Holographic interferometry techniques were used in the study of two-dimensional symmetric NACA 64A010 and Douglas Aircraft Company DSMA671 supercritical airfoil performance in the NASA Ames 2 ft x 2 ft transonic wind tunnel. Quantitative data obtained from the interferograms were compared to the surface pressure data. The excellent agreement obtained verified the accuracy of the flow visualization and demonstrated the potential for acquiring quantitative scalar results. Measurements of the inviscid flow speed and the boundary layer and wake velocity profiles were extracted from the interferograms and compared to laser Doppler velocimeter measurements. These results were also in good agreement. A method for acquiring real-time interferometric data in large-scale facilities was developed. This method, based on the point diffraction interferometer, was successfully tested in the Ames 2 ft x 2 ft transonic wind tunnel. The holographic and real-time interferometry methods were applied to the investigations of circulation control airfoils utilizing the Coanda effect. These results revealed the details of the jet interaction with the trailing edge boundary layer and the other parameters affecting the lift augmentation.

Bachalo, W. D.↗

NASA NTRS2001

All-Optical Micro Motors Based on Moving Gratings in Photosensitive Media

An all-optical micromotor with a rotor driven by a traveling wave of surface deformation of a stator being in contact with the rotor is being studied. Instead of an ultrasonic wave produced by an electrically driven piezoelectric actuator as in ultrasonic motors, the wave is a result of a photo-induced surface deformation of a photosensitive material produced by an incident radiation. A thin piezoelectric polymer will deform more easily LiNbO3 or metal when irradiated with light. The type of photosensitive material studied are piezoelectric polymers with and without coatings for connecting electrodes. In order to be considered as a possible candidate for micromotors, the material should exhibit surface deformation produced by a laser beam of the order of 10 microns. This is compared to the deformations produced by static holographic gratings studied in photorefractive crystals of LiNbO3 using high vertical resolution surface profilometer Dektak 3 and surface interferometer WYKO. An experimental setup showing the oscillations has been developed. The setup uses a chopped beam from an Argon ion laser to produce the deformation while a probe beam is reflected by the thin film into a fiber which is then detected on an oscilloscope. A ramp voltage signal generator will drive the piezoelectric film in another experiment to determine the resonance of the film. A current is generated when light is incident upon the film and this current can be measured. The reverse process has already been demonstrated in other piezoelectric actuators. Changing voltage, polarity, and frequency of the signal can easily generate vibrations similar to those when light is incident on the film. This can be compared to the effects of laser interaction with light absorbing fluids such as solutions of 2,9,16,23-Tetrakis(phenylthio)-29H, 31 H-phthalocyanine in chlorobenzene in capillary tubes, The possibility of using a liquid with the piezoelectric film would be a novel idea for a micromotor since the interaction of a single low power focused laser beam at 633 nm with such fluid produced an intensive circular motion.

Curley, M.↗

DOE OSTI2021

Distributed Acoustic Sensing Based on Coherent Microwave Photonics Interferometry

A microwave photonics method has been developed for measuring distributed acoustic signals. This method uses microwave-modulated low coherence light as a probe to interrogate distributed in-fiber interferometers, which are used to measure acoustic-induced strain. By sweeping the microwave frequency at a constant rate, the acoustic signals are encoded into the complex microwave spectrum. The microwave spectrum is transformed into the joint time–frequency domain and further processed to obtain the distributed acoustic signals. The method is first evaluated using an intrinsic Fabry Perot interferometer (IFPI). Acoustic signals of frequency up to 15.6 kHz were detected. The method was further demonstrated using an array of in-fiber weak reflectors and an external Michelson interferometer. Two piezoceramic cylinders (PCCs) driven at frequencies of 1700 Hz and 3430 Hz were used as acoustic sources. The experiment results show that the sensing system can locate multiple acoustic sources. The system resolves 20 nε when the spatial resolution is 5 cm. The recovered acoustic signals match the excitation signals in frequency, amplitude, and phase, indicating an excellent potential for distributed acoustic sensing (DAS).

47 OTHER INSTRUMENTATION↗

NASA NTRS2016

Sub-Femto-g Free Fall for Space-Based Gravitational Wave Observatories: LISA Pathfinder Results

We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2 +/- 0.1 fm s(exp -2)/square root of Hz, or (0.54 +/- 0.01) x 10(exp -15) g/square root of Hz, with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8 +/- 0.3) fm square root of Hz, about 2 orders of magnitude better than requirements. At f less than or equal to 0.5 mHz we observe a low-frequency tail that stays below 12 fm s(exp -2)/square root of Hz down to 0.1 mHz. This performance would allow for a space-based gravitational wave observatory with a sensitivity close to what was originally foreseen for LISA.

space science↗

NASA NTRS2012

A Precise Physical Orbit For The M-Dwarf Binary Gliese 268

We report high-precision interferometric and radial velocity (RV) observations of the M-dwarf binary Gl 268. Combining measurements conducted using the IOTA interferometer and the ELODIE and Harvard Center for Astrophysics RV instruments leads to a mass of 0.22596 plus-minus 0.00084 Mass compared to the sun for component A and 0.19230 plus-minus 0.00071 Mass compared to the sun for component B. The system parallax as determined by these observations is 0.1560 plus-minus 0.0030 arcsec - a measurement with 1.9% uncertainty in excellent agreement with Hipparcos (0.1572 plus-minus 0.0033). The absolute H-band magnitudes of the component stars are not well constrained by these measurements; however, we can place an approximate upper limit of 7.95 and 8.1 for Gl 268A and B, respectively.We test these physical parameters against the predictions of theoretical models that combine stellar evolution with high fidelity, non-gray atmospheric models. Measured and predicted values are compatible within 2sigma. These results are among the most precise masses measured for visual binaries and compete with the best adaptive optics and eclipsing binary results.

Barry, R. K.↗

NASA NTRS2013

Liquid Water Cloud Measurements Using the Raman Lidar Technique: Current Understanding and Future Research Needs

This paper describes recent work in the Raman lidar liquid water cloud measurement technique. The range-resolved spectral measurements at the National Aeronautics and Space Administration Goddard Space Flight Center indicate that the Raman backscattering spectra measured in and below low clouds agree well with theoretical spectra for vapor and liquid water. The calibration coefficients of the liquid water measurement for the Raman lidar at the Atmospheric Radiation Measurement Program Southern Great Plains site of the U.S. Department of Energy were determined by comparison with the liquid water path (LWP) obtained with Atmospheric Emitted Radiance Interferometer (AERI) and the liquid water content (LWC) obtained with the millimeter wavelength cloud radar and water vapor radiometer (MMCR-WVR) together. These comparisons were used to estimate the Raman liquid water cross-sectional value. The results indicate a bias consistent with an effective liquid water Raman cross-sectional value that is 28%-46% lower than published, which may be explained by the fact that the difference in the detectors' sensitivity has not been accounted for. The LWP of a thin altostratus cloud showed good qualitative agreement between lidar retrievals and AERI. However, the overall ensemble of comparisons of LWP showed considerable scatter, possibly because of the different fields of view of the instruments, the 350-m distance between the instruments, and the horizontal inhomogeneity of the clouds. The LWC profiles for a thick stratus cloud showed agreement between lidar retrievals andMMCR-WVR between the cloud base and 150m above that where the optical depth was less than 3. Areas requiring further research in this technique are discussed.

vapor and liquid water↗

NASA NTRS2008

Application of High-Temperature Extrinsic Fabry-Perot Interferometer Strain Sensor

In this presentation to the NASA Aeronautics Sensor Working Group the application of a strain sensor is outlined. The high-temperature extrinsic Fabry-Perot interferometer (EFPI) strain sensor was developed due to a need for robust strain sensors that operate accurately and reliably beyond 1800 F. Specifically, the new strain sensor would provide data for validating finite element models and thermal-structural analyses. Sensor attachment techniques were also developed to improve methods of handling and protecting the fragile sensors during the harsh installation process. It was determined that thermal sprayed attachments are preferable even though cements are simpler to apply as cements are more prone to bond failure and are often corrosive. Previous thermal/mechanical cantilever beam testing of EFPI yielded very little change to 1200 F, with excellent correlation with SG to 550 F. Current combined thermal/mechanical loading for sensitivity testing is accomplished by a furnace/cantilever beam loading system. Dilatometer testing has can also be used in sensor characterization to evaluate bond integrity, evaluate sensitivity and accuracy and to evaluate sensor-to-sensor scatter, repeatability, hysteresis and drift. Future fiber optic testing will examine single-mode silica EFPIs in a combined thermal/mechanical load fixture on C-C and C-SiC substrates, develop a multi-mode Sapphire strain-sensor, test and evaluate high-temperature fiber Bragg Gratings for use as strain and temperature sensors and attach and evaluate a high-temperature heat flux gauge.

Piazza, Anthony↗

DOE OSTI2022

Differently Structured Fabry-Perot Interferometers for Gas Pressure Monitoring

In this study, we present an experimental comparison of gas pressure sensors based on differently structured extrinsic Fabry-Pérot interferometers (FPIs). Different fabrication techniques were adopted to foster the practical realization of these sensors. A novel photonic crystal fiber (PCF) based FPI with an angle cleaved end face that enables gas to easily flow in and out of the cavity while also avoiding the mixed signal from the cascaded structure is also presented. We measured helium gas pressure from 0.1 MPa (atmospheric pressure) to 5 MPa at room temperature and obtained a gas pressure sensitivity coefficient of 0.5±0.01 nm/MPa. Furthermore, the gas pressure sensitivities are numerically analyzed to validate the experimental results.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1986

A compact density condensation around L1551-IRS 5: 2.7mm continuum observations with 4" resolution

The dark cloud L1551 contains the best known examples of bipolar molecular outflow. Such outflows are assumed to be driven by winds from young stars embedded in a cloud but the mechanism for collimation of the outflows is still in doubt, though it has been much debated. Among the possibilities put forth to date are intrinsically anisotropic stellar winds, isotropic stellar winds collimated by interstellar toroidal shaped clouds on the order of 10(17) cm in size, or circumstellar disks of order 10(15) cm in size. Because the outflow in L1551 as revealed by the Very Large Array (VLA) cm continuum observations is collimated even at the arc second level it seems as though the stellar wind powering the outflow must either be initially anisotropic or be collimated by something very close to the star, such as a circumstellar disk. We have observed L1551 in the continuum at 2.7 mm with the OVRO millimeter-wave interferometer in the winter of 1983-4 and again, more extensively, in 1985-6. The resulting map shows for the first time direct evidence for a density condensation capable of collimating an initially isotropic flow from IRS 5. This map made from data taken in 1985-6 with projected baselines up to 100 m in length (37k lambda). It has been cleaned and reconstructed with a 4'' gaussian beam. It shows a nearly unresolved source with a suggestion of extension at the 3'' level (assuming a gaussian source shape). The integrated flux density in this map is 170 mJy. A composite spectrum of L1551 is presented which shows that the flux at 2.7 mm is due to the thermal radiation from dust that is also seen at shorter wavelengths. Very little of it can be due to the continuation of the nearly flat cm wavelength spectrum which is assumed to be from thermal bremsstrahlung radiation. The map and spectrum provide strong constraints on the size, temperature, and optical depth of the density condensation surrounding IRS 5.

Keene, J.↗

NASA NTRS1993

The Hubble Space Telescope fine guidance system operating in the coarse track pointing control mode

The Hubble Space Telescope (HST) Fine Guidance System has set new standards in pointing control capability for earth orbiting spacecraft. Two precision pointing control modes are implemented in the Fine Guidance System; one being a Coarse Track Mode which employs a pseudo-quadrature detector approach and the second being a Fine Mode which uses a two axis interferometer implementation. The Coarse Track Mode was designed to maintain FGS pointing error to within 20 milli-arc seconds (rms) when guiding on a 14.5 Mv star. The Fine Mode was designed to maintain FGS pointing error to less than 3 milli-arc seconds (rms). This paper addresses the HST FGS operating in the Coarse Track Mode. An overview of the implementation, the operation, and both the predicted and observed on orbit performance is presented. The discussion includes a review of the Fine Guidance System hardware which uses two beam steering Star Selector servos, four photon counting photomultiplier tube detectors, as well as a 24 bit microprocessor, which executes the control system firmware. Unanticipated spacecraft operational characteristics are discussed as they impact pointing performance. These include the influence of spherically aberrated star images as well as the mechanical shocks induced in the spacecraft during and following orbital day/night terminator crossings. Computer modeling of the Coarse Track Mode verifies the observed on orbit performance trends in the presence of these optical and mechanical disturbances. It is concluded that the coarse track pointing control function is performing as designed and is providing a robust pointing control capability for the Hubble Space Telescope.

Whittlesey, Richard↗

NASA NTRS1995

Advanced Modeling of Micromirror Devices

The flexure-beam micromirror device (FBMD) is a phase only piston style spatial light modulator demonstrating properties which can be used for phase adaptive corrective optics. This paper presents a complete study of a square FBMD, from advanced model development through final device testing and model verification. The model relates the electrical and mechanical properties of the device by equating the electrostatic force of a parallel-plate capacitor with the counter-acting spring force of the device's support flexures. The capacitor solution is derived via the Schwartz-Christoffel transformation such that the final solution accounts for non-ideal electric fields. The complete model describes the behavior of any piston-style device, given its design geometry and material properties. It includes operational parameters such as drive frequency and temperature, as well as fringing effects, mirror surface deformations, and cross-talk from neighboring devices. The steps taken to develop this model can be applied to other micromirrors, such as the cantilever and torsion-beam designs, to produce an advanced model for any given device. The micromirror devices studied in this paper were commercially fabricated in a surface micromachining process. A microscope-based laser interferometer is used to test the device in which a beam reflected from the device modulates a fixed reference beam. The mirror displacement is determined from the relative phase which generates a continuous set of data for each selected position on the mirror surface. Plots of this data describe the localized deflection as a function of drive voltage.

Michalicek, M. Adrian↗

DOE OSTI2024

Tailoring coherent charge transport in graphene by deterministic defect generation

Harnessing the wave-nature of charge carriers in solid state devices, electron optics investigates and exploits coherent phenomena, in analogy with optics and photonics. Typically, this requires complex electronic devices leveraging macroscopically coherent charge transport in two-dimensional electron gases and superconductors. Here, collective coherent effects are induced in a simple counterintuitive architecture by defect engineering. Deterministically introduced lattice defects in graphene enable the phase coherent charge transport by playing the role of potential barriers, instead of scattering centres as conventionally considered. Thus, graphene preserves its quasi-ballistic quantum transport and can support phase-matched charge carrier waves. Based on this approach, multiple electronic Fabry-Pèrot cavities are formed by creating periodically alternating defective and pristine nano-stripes through low energy electron-beam irradiation. Indeed, defective stripes behave as partially reflecting mirrors and resonantly confine the charge carrier waves within the pristine areas, giving rise to Fabry-Pèrot resonant modes. These modes experimentally manifest as sheet resistance oscillations, as also confirmed by Landauer-Büttiker simulations. Moreover, these coherent phenomena survive up to 30 K for both polarities of charge carriers, contrarily to traditional monopolar electrostatically created Fabry-Pèrot interferometers. Our study positions defective graphene as an innovative platform for coherent electronic devices, with potential applications in nano and quantum technologies.

Melchioni, Nicola↗

NASA NTRS2003

Multiple-etalon systems for the Advanced Technology Solar Telescope

Multiple etalon systems are discussed that meet the science requirements for a narrow-passband imaging system for the 4-meter National Solar Observatory (NSO)/Advance Technology Solar Telescope (ATST). A multiple etalon system can provide an imaging interferometer that works in four distinct modes: as a spectro-polarimeter, a filter-vector magnetograph, an intermediate-band imager, and broadband high-resolution imager. Specific dual and triple etalon configurations are described that provide a spectrographic passband of 2.0-3.5 micron and reduce parasitic light levels to 10(exp -4) as required for precise polarization measurement, e.g., Zeeman measurements of magnetic sensitive lines. A TESOS-like (Telecentric Etalon SOlar Spectrometer) triple etalon system provides a spectral purity of 10(exp -5). The triple designs have the advantage of reducing the finesse requirement on each etalon; allow the use of more stable blocking filters, and have very high spectral purity. A dual-etalon double-pass (Cavallini-like) system can provide a competing configuration. Such a dual-etalon design can provide high contrast. The selection of the final focal plane instrument will depend on a trade-off between an ideal instrument and practical reality. The trade study will include the number of etalons, their aperture sizes, complexities of the optical train, number of blocking filters, configuration of the electronic control system, computer interfaces, temperature controllers, etalon controllers, and their associated feedback electronics. The heritage of single and multiple etalon systems comes from their use in several observatories, including the Marshall Space Flight Center (MSFC) Solar Observatory, Sacramento Peak Observatory (NSO), and Kiepenheuer-Institut fur Sonnenphysik (KIS, Germany), Mees Solar Observatory (University of Hawaii), and Arcetri Astrophysical Observatory (Italy). The design of the ATST multiple etalon system will benefit from the experience gained at these observatories.

Gary, G. Allen↗

NASA NTRS2010

Vacuum-Compatible Wideband White Light and Laser Combiner Source System

For the Space Interferometry Mission (SIM) Spectrum Calibration Development Unit (SCDU) testbed, wideband white light is used to simulate starlight. The white light source mount requires extremely stable pointing accuracy (<3.2 microradians). To meet this and other needs, the laser light from a single-mode fiber was combined, through a beam splitter window with special coating from broadband wavelengths, with light from multimode fiber. Both lights were coupled to a photonic crystal fiber (PCF). In many optical systems, simulating a point star with broadband spectrum with stability of microradians for white light interferometry is a challenge. In this case, the cameras use the white light interference to balance two optical paths, and to maintain close tracking. In order to coarse align the optical paths, a laser light is sent into the system to allow tracking of fringes because a narrow band laser has a great range of interference. The design requirements forced the innovators to use a new type of optical fiber, and to take a large amount of care in aligning the input sources. The testbed required better than 1% throughput, or enough output power on the lowest spectrum to be detectable by the CCD camera (6 nW at camera). The system needed to be vacuum-compatible and to have the capability for combining a visible laser light at any time for calibration purposes. The red laser is a commercially produced 635-nm laser 5-mW diode, and the white light source is a commercially produced tungsten halogen lamp that gives a broad spectrum of about 525 to 800 nm full width at half maximum (FWHM), with about 1.4 mW of power at 630 nm. A custom-made beam splitter window with special coating for broadband wavelengths is used with the white light input via a 50-mm multi-mode fiber. The large mode area PCF is an LMA-8 made by Crystal Fibre (core diameter of 8.5 mm, mode field diameter of 6 mm, and numerical aperture at 625 nm of 0.083). Any science interferometer that needs a tracking laser fringe to assist in alignment can use this system.

Azizi, Alineza↗